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User Project Publications


Open list in Research Information System

2019

CIRCA: Towards a Modular and Extensible Framework for Approximate Circuit Generation

L.M. Witschen, T. Wiersema, H. Ghasemzadeh Mohammadi, M. Awais, M. Platzner, Microelectronics Reliability (2019), 99, pp. 277-290

Existing approaches and tools for the generation of approximate circuits often lack generality and are restricted to certain circuit types, approximation techniques, and quality assurance methods. Moreover, only few tools are publicly available. This hinders the development and evaluation of new techniques for approximating circuits and their comparison to previous approaches. In this paper, we first analyze and classify related approaches and then present CIRCA, our flexible framework for search-based approximate circuit generation. CIRCA is developed with a focus on modularity and extensibility. We present the architecture of CIRCA with its clear separation into stages and functional blocks, report on the current prototype, and show initial experiments.


Higher-order contributions and nonperturbative effects in the nondegenerate nonlinear optical absorption of semiconductors using a two-band model

W. Hannes, T. Meier, Physical Review B (2019), 99(12)

DOI


Molecular Doping of PCPDT-BT Copolymers: Comparison of Molecular Complexes with and Without Integer Charge Transfer

C. Dong, S. Schumacher, 2019

<jats:p>&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;Molecular doping in conjugated polymers is a crucial process for their application in organic photovoltaics and optoelectronics. In the present work we theoretically investigate p-type molecu- lar doping in a series of (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b”]dithiophene)-alt- 4,7-(2,1,3-benzothiadiazole)] (PCPDT-BT) conjugated oligomers with different lengths and three widely-used dopants with different electron affinities, namely F4TCNQ, F6TCNNQ, and CN6-CP. We study in detail the molecular geometry of possible oligomer-dopant complexes and its influence on the doping mechanisms and electronic system properties. We find that the mechanisms of dop- ing and charge transfer observed sensitively depend on the specific geometry of the oligomer-dopant complexes. For a given complex different geometries may exist, some of which show transfer of an entire electron from the oligomer chain onto the dopant molecule resulting in an integer-charge transfer complex, leaving the system in a ground state with broken spin symmetry. In other ge- ometries merely hybridization of oligomer and dopant frontier orbitals occurs with partial charge transfer but spin-symmetric ground state. Considering the resulting electronic density of states both cases may well contribute to an increased electrical conductivity of corresponding film samples while the underlying physical mechanisms are entirely different. &lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;</jats:p>


Optical Vortex Core Switching in Spinor Polariton Condensates

M. Pukrop, S. Schumacher, X. Ma, in: arXiv:1907.10974, 2019

Vortices are topological objects carrying quantized orbital angular momentum, also known as topological charge, and have been widely studied in many physical systems for their applicability in information storage and processing. Here we focus on vortices in semiconductor microcavity polariton condensates. In systems with spin degree of freedom the elementary excitations are so called half-vortices. A half-vortex carries a quantum circulation only in one of the two spin components. It has lower energy in comparison with a full-vortex and, importantly, has a circularly polarized density peak in the vortex core region, while elsewhere the condensate is linearly polarized. We demonstrate the spontaneous formation of localized half-vortices in spinor polariton condensates, non-resonantly excited by a linearly polarized ring pump. The pseudospin structure of the condensate includes a TE-TM splitting leading to effective spin-orbit coupling, resulting in solutions with broken cylindrical symmetry. The cross-interaction between different spin components provides an efficient method to realize optical vortex core switching between left- and right-circularly polarized states. This switching can be easily detected by measuring the polarization resolved intensity in the vortex core region and it can also be applied to higher order half-vortex states.


Oxygen and potassium vacancies in KTP calculated from first principles

A. Bocchini, S. Neufeld, U. Gerstmann, W.G. Schmidt, Journal of Physics: Condensed Matter (2019)

DOI


Deep reinforcement learning for scheduling in large-scale networked control systems

A. Redder, A. Ramaswamy, D. Quevedo, in: Proceedings of the 8th IFAC Workshop on Distributed Estimation and Control in Networked Systems, 2019

This work considers the problem of control and resource allocation in networked systems. To this end, we present DIRA a Deep reinforcement learning based Iterative Resource Allocation algorithm, which is scalable and control-aware. Our algorithm is tailored towards large-scale problems where control and scheduling need to act jointly to optimize performance. DIRA can be used to schedule general time-domain optimization based controllers. In the present work, we focus on control designs based on suitably adapted linear quadratic regulators. We apply our algorithm to networked systems with correlated fading communication channels. Our simulations show that DIRA scales well to large scheduling problems.


Quasiparticle and excitonic effects in the optical response of KNbO3

F. Schmidt, A. Riefer, W.G. Schmidt, A. Schindlmayr, M. Imlau, F. Dobener, N. Mengel, S. Chatterjee, S. Sanna, Physical Review Materials (2019)

DOI


Guided Source Separation Meets a Strong ASR Backend: Hitachi/Paderborn University Joint Investigation for Dinner Party ASR

N. Kanda, C. Boeddeker, J. Heitkaemper, Y. Fujita, S. Horiguchi, R. Haeb-Umbach, in: INTERSPEECH 2019, Graz, Austria, 2019

In this paper, we present Hitachi and Paderborn University’s joint effort for automatic speech recognition (ASR) in a dinner party scenario. The main challenges of ASR systems for dinner party recordings obtained by multiple microphone arrays are (1) heavy speech overlaps, (2) severe noise and reverberation, (3) very natural onversational content, and possibly (4) insufficient training data. As an example of a dinner party scenario, we have chosen the data presented during the CHiME-5 speech recognition challenge, where the baseline ASR had a 73.3% word error rate (WER), and even the best performing system at the CHiME-5 challenge had a 46.1% WER. We extensively investigated a combination of the guided source separation-based speech enhancement technique and an already proposed strong ASR backend and found that a tight combination of these techniques provided substantial accuracy improvements. Our final system achieved WERs of 39.94% and 41.64% for the development and evaluation data, respectively, both of which are the best published results for the dataset. We also investigated with additional training data on the official small data in the CHiME-5 corpus to assess the intrinsic difficulty of this ASR task.


Stofftransport und Fluidmechanik bei der Tropfenbildung unter Berücksichtigung von Marangonikonvektion mittels CFD

C. Wecker, A. Schulz, J. Heine, H. Bart, E. Kenig. Stofftransport und Fluidmechanik bei der Tropfenbildung unter Berücksichtigung von Marangonikonvektion mittels CFD. 2019.


Divide and Compact - Stochastic Space Compaction for Faster-than-At-Speed Test

A. Sprenger, S. Hellebrand, Journal of Circuits, Systems and Computers (2019)

DOI


Jump Search: A Fast Technique for the Synthesis of Approximate Circuits

L.M. Witschen, H. Ghasemzadeh Mohammadi, M. Artmann, M. Platzner, in: Proceedings of the 2019 on Great Lakes Symposium on VLSI - GLSVLSI '19, ACM, 2019

State-of-the-art frameworks for generating approximate circuits automatically explore the search space in an iterative process - often greedily. Synthesis and verification processes are invoked in each iteration to evaluate the found solutions and to guide the search algorithm. As a result, a large number of approximate circuits is subjected to analysis - leading to long runtimes - but only a few approximate circuits might form an acceptable solution. In this paper, we present our Jump Search (JS) method which seeks to reduce the runtime of an approximation process by reducing the number of expensive synthesis and verification steps. To reduce the runtime, JS computes impact factors for each approximation candidate in the circuit to create a selection of approximate circuits without invoking synthesis or verification processes. We denote the selection as path from which JS determines the final solution. In our experimental results, JS achieved speed-ups of up to 57x while area savings remain comparable to the reference search method, Simulated Annealing.


Stepwise Growth of Ruthenium Terpyridine Complexes on Au Surfaces

S.K. Peter, C. Kaulen, A. Hoffmann, W. Ogieglo, S. Karthäuser, M. Homberger, S. Herres-Pawlis, U. Simon, The Journal of Physical Chemistry C (2019), 123(11), pp. 6537-6548

DOI


Intensity-dependent degenerate and non-degenerate nonlinear optical absorption of direct-gap semiconductors

W. Hannes, L. Krauß-Kodytek, C. Ruppert, M. Betz, T. Meier, in: Ultrafast Phenomena and Nanophotonics XXIII, 2019

DOI


Curved Polar Dibenzocoronene Esters and Imides versus Their Planar Centrosymmetric Homologs: Photophysical and Optoelectronic Analysis

J. Vollbrecht, C. Wiebeler, H. Bock, S. Schumacher, H. Kitzerow, The Journal of Physical Chemistry C (2019), 123(7), pp. 4483-4492

DOI


Excited-state band mapping and momentum-resolved ultrafast population dynamics in In/Si(111) nanowires investigated with XUV-based time- and angle-resolved photoemission spectroscopy

C.W. Nicholson, M. Puppin, A. Lücke, U. Gerstmann, M. Krenz, W.G. Schmidt, L. Rettig, R. Ernstorfer, M. Wolf, Physical Review B (2019), 99(15)

DOI


Integration of Neural Networks and Probabilistic Spatial Models for Acoustic Blind Source Separation

L. Drude, R. Haeb-Umbach, IEEE Journal of Selected Topics in Signal Processing (2019)

We formulate a generic framework for blind source separation (BSS), which allows integrating data-driven spectro-temporal methods, such as deep clustering and deep attractor networks, with physically motivated probabilistic spatial methods, such as complex angular central Gaussian mixture models. The integrated model exploits the complementary strengths of the two approaches to BSS: the strong modeling power of neural networks, which, however, is based on supervised learning, and the ease of unsupervised learning of the spatial mixture models whose few parameters can be estimated on as little as a single segment of a real mixture of speech. Experiments are carried out on both artificially mixed speech and true recordings of speech mixtures. The experiments verify that the integrated models consistently outperform the individual components. We further extend the models to cope with noisy, reverberant speech and introduce a cross-domain teacher–student training where the mixture model serves as the teacher to provide training targets for the student neural network.


Diffusion of Alkali Metals in Polycrystalline CuInSe2 and Their Role in the Passivation of Grain Boundaries

M. Chugh, .T.D... Kühne, H. Mirhosseini, , ACS Applied Materials & Interfaces (2019), 11(16), pp. 1944-8244

DOI


Properties of Co-Evaporated RbInSe2 Thin Films

T. Kodalle, R. Kormath Madam Raghupathy, T. Bertram, N. Maticiuc, H.A. Yetkin, R. Gunder, R. Schlatmann, T.D. Kühne, C.A. Kaufmann, H. Mirhosseini, physica status solidi (RRL)--Rapid Research Letters (2019), 13(3), pp. 1800564

DOI


A Branch and Bound Approach for Large Pre-Marshalling Problems

S. Tanaka, K. Tierney, C. Parreño-Torres, R. Alvarez-Valdes, R. Ruiz, European Journal of Operational Research (2019), pp. 211-225

DOI


Diffusion Limited Evaporation of a Binary Liquid Film

R.S. Chatwell, M. Heinen, J. Vrabec, International Journal of Heat and Mass Transfer (2019), 132, pp. 1296-1305

DOI


Water Splitting Reaction at Polar Lithium Niobate Surfaces

C. Dues, W.G. Schmidt, S. Sanna, ACS Omega (2019), pp. 3850-3859

DOI


A Study on Online Source Extraction in the Presence of Changing Speaker Positions

J. Heitkaemper, T. Feher, M. Freitag, R. Haeb-Umbach, in: International Conference on Statistical Language and Speech Processing 2019, Ljubljana, Slovenia, 2019

Multi-talker speech and moving speakers still pose a significant challenge to automatic speech recognition systems. Assuming an enrollment utterance of the target speakeris available, the so-called SpeakerBeam concept has been recently proposed to extract the target speaker from a speech mixture. If multi-channel input is available, spatial properties of the speaker can be exploited to support the source extraction. In this contribution we investigate different approaches to exploit such spatial information. In particular, we are interested in the question, how useful this information is if the target speaker changes his/her position. To this end, we present a SpeakerBeam-based source extraction network that is adapted to work on moving speakers by recursively updating the beamformer coefficients. Experimental results are presented on two data sets, one with articially created room impulse responses, and one with real room impulse responses and noise recorded in a conference room. Interestingly, spatial features turn out to be advantageous even if the speaker position changes.


Ein Finite-Volumen Ansatz für den Stoffübergang an bewegten Phasengrenzflächen

A. Schulz, C. Wecker, E. Kenig. Ein Finite-Volumen Ansatz für den Stoffübergang an bewegten Phasengrenzflächen. 2019.


Stofftransport bei der Tropfenbildung

J. Heine, C. Wecker, E. Kenig, H. Bart. Stofftransport bei der Tropfenbildung. 2019.


Characterization of the linear-acoustic material behavior of fiber-reinforced composites using lamb waves

S. Johannesmann, M. Webersen, J. Düchting, L. Claes, B. Henning, in: 45th Annual Review of Progress in Quantitative Nondestructive Evaluation , 2019

DOI


Automating Multi-Label Classification Extending ML-Plan

M.D. Wever, F. Mohr, A. Tornede, E. Hüllermeier, 2019

Existing tools for automated machine learning, such as Auto-WEKA, TPOT, auto-sklearn, and more recently ML-Plan, have shown impressive results for the tasks of single-label classification and regression. Yet, there is only little work on other types of machine learning problems so far. In particular, there is almost no work on automating the engineering of machine learning solutions for multi-label classification (MLC). We show how the scope of ML-Plan, an AutoML-tool for multi-class classification, can be extended towards MLC using MEKA, which is a multi-label extension of the well-known Java library WEKA. The resulting approach recursively refines MEKA's multi-label classifiers, nesting other multi-label classifiers for meta algorithms and single-label classifiers provided by WEKA as base learners. In our evaluation, we find that the proposed approach yields strong results and performs significantly better than a set of baselines we compare with.


New Kids in Lactide Polymerization: Highly Active and Robust Iron Guanidine Complexes as Superior Catalysts

R.D. Rittinghaus, P.M. Schäfer, P. Albrecht, C. Conrads, A. Hoffmann, A.N. Ksiazkiewicz, O. Bienemann, A. Pich, S. Herres-Pawlis, ChemSusChem (2019), 12(10), pp. 2161-2165

Abstract Polylactide is a biodegradable versatile material based on annually renewable resources and thus CO2-neutral in its lifecycle. Until now, tin(II)octanoate [Sn(Oct2)] was used as catalyst for the industrial ring-opening polymerization of lactide in spite of its cytotoxicity. On the way towards a sustainable catalyst, three iron(II) hybrid guanidine complexes were investigated concerning their molecular structure and applied to the ring-opening polymerization of lactide. The complexes could polymerize unpurified technical-grade rac-lactide as well as recrystallized l-lactide to long-chain polylactide in bulk with monomer/initiator ratios of more than 5000:1 in a controlled manner following the coordination–insertion mechanism. For the first time, a biocompatible complex has surpassed Sn(Oct)2 in its polymerization activity under industrially relevant conditions.


Hyper-Reactive Tabu Search for MaxSAT

C. Ansótegui, B. Heymann, J. Pon, M. Sellmann, K. Tierney, in: Learning and Intelligent Optimization, Springer International Publishing, 2019, pp. 309-325

DOI


Realization of all-optical vortex switching in exciton-polariton condensates

X. Ma, B. Berger, M. Assmann, R. Driben, T. Meier, C. Schneider, S. Höfling, S. Schumacher, in: arXiv:1907.03171, 2019

Vortices are topological objects representing the circular motion of a fluid. With their additional degree of freedom, the 'vorticity', they have been widely investigated in many physical systems and different materials for fundamental interest and for applications in data storage and information processing. Vortices have also been observed in non-equilibrium exciton-polariton condensates in planar semiconductor microcavities. There they appear spontaneously or can be created and pinned in space using ring-shaped optical excitation profiles. However, using the vortex state for information processing not only requires creation of a vortex but also efficient control over the vortex after its creation. Here we demonstrate a simple approach to control and switch a localized polariton vortex between opposite states. In our scheme, both the optical control of vorticity and its detection through the orbital angular momentum of the emitted light are implemented in a robust and practical manner.


Bloch oscillations of multidimensional dark soliton wave packets and light bullets

R. Driben, X. Ma, S. Schumacher, T. Meier, Optics Letters (2019), 44(6)

DOI


Controlling the strength of interaction between carbon dioxide and nitrogen-rich carbon materials by molecular design

R. Walczak, A. Savateev, J. Heske, N.V. Tarakina, S. Sahoo, J.D. Epping, T.D. Kühne, B. Kurpil, M. Antonietti, M. Oschatz, Sustainable Energy Fuels (2019), pp. -

Thermal treatment of hexaazatriphenylene-hexacarbonitrile (HAT-CN) in the temperature range from 500 °C to 700 °C leads to precise control over the degree of condensation{,} and thus atomic construction and porosity of the resulting C2N-type materials. Depending on the condensation temperature of HAT-CN{,} nitrogen contents of more than 30 at% can be reached. In general{,} these carbons show adsorption properties which are comparable to those known for zeolites but their pore size can be adjusted over a wider range. At condensation temperatures of 525 °C and below{,} the uptake of nitrogen gas remains negligible due to size exclusion{,} but the internal pores are large and polarizing enough that CO2 can still adsorb on part of the internal surface. This leads to surprisingly high CO2 adsorption capacities and isosteric heat of adsorption of up to 52 kJ mol−1. Theoretical calculations show that this high binding enthalpy arises from collective stabilization effects from the nitrogen atoms in the C2N layers surrounding the carbon atom in the CO2 molecule and from the electron acceptor properties of the carbon atoms from C2N which are in close proximity to the oxygen atoms in CO2. A true CO2 molecular sieving effect is achieved for the first time in such a metal-free organic material with zeolite-like properties{,} showing an IAST CO2/N2 selectivity of up to 121 at 298 K and a N2/CO2 ratio of 90/10 without notable changes in the CO2 adsorption properities over 80 cycles.


Alkali Atoms Diffusion Mechanism in CuInSe2 Explained by Kinetic Monte Carlo Simulations

R. Kormath Madam Raghupathy, T.D. Kühne, G. Henkelman, H. Mirhosseini, Advanced Theory and Simulations (2019), pp. 1900036

DOI


Kirkwood-Buff Integration: A Promising Route to Entropic Properties?

R. Fingerhut, J. Vrabec, Fluid Phase Equilibria (2019), pp. 270-281

DOI


Quantification of frequency-dependent absorption phenomena

L. Claes, S. Johannesmann, E. Baumhögger, B. Henning, in: 2019 International Congress on Ultrasonics, 2019

DOI


Undiscovered potential: Ge catalysts for lactide polymerization

S. Herres-Pawlis, R.D. Rittinghaus, J. Tremmel, A. Ruzicka, C. Conrads, P. Albrecht, A. Hoffmann, A. Ksiazkiewicz, A. Pich, R. Jambor, Chemistry – A European Journal (2019)

DOI


Algorithm Selection as Recommendation: From Collaborative Filtering to Dyad Ranking

A. Tornede, M.D. Wever, E. Hüllermeier, in: Proceedings - 29. Workshop Computational Intelligence, Dortmund, 28. - 29. November 2019, KIT Scientific Publishing, Karlsruhe, 2019, pp. 135-146


Reduktion von parasitären Strömungen in Mehrphasensimulationen durch Verwendung der Height-Function Methode

A. Zibart, E. Kenig. Reduktion von parasitären Strömungen in Mehrphasensimulationen durch Verwendung der Height-Function Methode. 2019.


Numerische Untersuchungen zum Stofftransport und Fluidmechanik bei der Tropfenbildung

C. Wecker, A. Schulz, J. Heine, H. Bart, E. Kenig. Numerische Untersuchungen zum Stofftransport und Fluidmechanik bei der Tropfenbildung. 2019.


Modellierung und Optimierung von makroverkapselten Latentwärmespeicherelementen

M. Grabo, S. Christoph, E. Kenig. Modellierung und Optimierung von makroverkapselten Latentwärmespeicherelementen. 2019.


Accurate Sampling with Noisy Forces from Approximate Computing

V. Rengaraj, M. Lass, C. Plessl, T. Kühne, in: arXiv:1907.08497, 2019

In scientific computing, the acceleration of atomistic computer simulations by means of custom hardware is finding ever growing application. A major limitation, however, is that the high efficiency in terms of performance and low power consumption entails the massive usage of low-precision computing units. Here, based on the approximate computing paradigm, we present an algorithmic method to rigorously compensate for numerical inaccuracies due to low-accuracy arithmetic operations, yet still obtaining exact expectation values using a properly modified Langevin-type equation.


Acoustic absorption measurement for the determination of the volume viscosity of pure fluids / Messverfahren für die akustischen Absorption zur Bestimmung der Volumenviskosität reiner Fluide

L. Claes, L.M. Hülskämper, E. Baumhögger, N. Feldmann, R.S. Chatwell, J. Vrabec, B. Henning, tm - Technisches Messen (2019), pp. 2-6

DOI


A General Algorithm to Calculate the Inverse Principal p-th Root of Symmetric Positive Definite Matrices

D. Richters, M. Lass, A. Walther, C. Plessl, T. Kühne, Communications in Computational Physics (2019), 25(2), pp. 564-585

We address the general mathematical problem of computing the inverse p-th root of a given matrix in an efficient way. A new method to construct iteration functions that allow calculating arbitrary p-th roots and their inverses of symmetric positive definite matrices is presented. We show that the order of convergence is at least quadratic and that adaptively adjusting a parameter q always leads to an even faster convergence. In this way, a better performance than with previously known iteration schemes is achieved. The efficiency of the iterative functions is demonstrated for various matrices with different densities, condition numbers and spectral radii.


Externally Controlled Lotka-Volterra Dynamics in a Linearly Polarized Polariton Fluid

M. Pukrop, S. Schumacher, in: arXiv:1903.12534, 2019

Spontaneous formation of transverse patterns is ubiquitous in nonlinear dynamical systems of all kinds. An aspect of particular interest is the active control of such patterns. In nonlinear optical systems this can be used for all-optical switching with transistor-like performance, for example realized with polaritons in a planar quantum-well semiconductor microcavity. Here we focus on a specific configuration which takes advantage of the intricate polarization dependencies in the interacting optically driven polariton system. Besides detailed numerical simulations of the coupled light-field exciton dynamics, in the present paper we focus on the derivation of a simplified population competition model giving detailed insight into the underlying mechanisms from a nonlinear dynamical systems perspective. We show that such a model takes the form of a generalized Lotka-Volterra system for two competing populations explicitly including a source term that enables external control. We present a comprehensive analysis both of the existence and stability of stationary states in the parameter space spanned by spatial anisotropy and external control strength. We also construct phase boundaries in non-trivial regions and characterize emerging bifurcations. The population competition model reproduces all key features of the switching observed in full numerical simulations of the rather complex semiconductor system and at the same time is simple enough for a fully analytical understanding of the system dynamics.


Opposing Electronic and Nuclear Quantum Effects on Hydrogen Bonds in H2O and D2O

T. Clark, J. Heske, T.D. Kühne, ChemPhysChem (2019), 20, pp. 1-6

Abstract The effect of extending the O−H bond length(s) in water on the hydrogen-bonding strength has been investigated using static ab initio molecular orbital calculations. The “polar flattening” effect that causes a slight σ-hole to form on hydrogen atoms is strengthened when the bond is stretched, so that the σ-hole becomes more positive and hydrogen bonding stronger. In opposition to this electronic effect, path-integral ab initio molecular-dynamics simulations show that the nuclear quantum effect weakens the hydrogen bond in the water dimer. Thus, static electronic effects strengthen the hydrogen bond in H2O relative to D2O, whereas nuclear quantum effects weaken it. These quantum fluctuations are stronger for the water dimer than in bulk water.


Impact of intermolecular vibrational coupling effects on the sum-frequency generation spectra of the water/air interface

N.K.. Kaliannan, A. Henao Aristizabal, H. Wiebeler, F. Zysk, T. Ohto, Y. Nagata, T. D. Kühne, Molecular Physics (2019), pp. 1-10

DOI


Enhancement of the local asymmetry in the hydrogen bond network of liquid water by an ultrafast electric field pulse

H. Elgabarty, N.K. Kaliannan, T.D. Kühne, Scientific Reports (2019), 9(1), pp. 1-8

DOI


Investigation of Near-Surface Defects of Nanodiamonds by High-Frequency EPR and DFT Calculation

F.H. Cho, Z. Peng, T. Biktagirov, U. Gerstmann, S. Takahashi, The Journal of Chemical Physics (2019), 150(13), pp. 134702

DOI


Diffusion of Methane in Supercritical Carbon Dioxide Across the Widom Line

G. Guevara-Carrion, S. Ancherbak, A. Mialdun, J. Vrabec, V. Shevtsova, Scientific Reports (2019), 9

DOI


Stepwise Growth of Ruthenium Terpyridine Complexes on Au Surfaces

S.K. Peter, C. Kaulen, A. Hoffmann, W. Ogieglo, S. Karthäuser, M. Homberger, S. Herres-Pawlis, U. Simon, The Journal of Physical Chemistry C (2019), 123(11), pp. 6537-6548

DOI


Random network models with variable disorder of geometry

A. Klümper, W. Nuding, A. Sedrakyan, Physical Review B (2019), 100, pp. 140201

DOI


Multi-Channel Block-Online Source Extraction based on Utterance Adaptation

J.M. Martin-Donas, J. Heitkaemper, R. Haeb-Umbach, A.M. Gomez, A.M. Peinado, in: INTERSPEECH 2019, Graz, Austria, 2019

This paper deals with multi-channel speech recognition in scenarios with multiple speakers. Recently, the spectral characteristics of a target speaker, extracted from an adaptation utterance, have been used to guide a neural network mask estimator to focus on that speaker. In this work we present two variants of speakeraware neural networks, which exploit both spectral and spatial information to allow better discrimination between target and interfering speakers. Thus, we introduce either a spatial preprocessing prior to the mask estimation or a spatial plus spectral speaker characterization block whose output is directly fed into the neural mask estimator. The target speaker’s spectral and spatial signature is extracted from an adaptation utterance recorded at the beginning of a session. We further adapt the architecture for low-latency processing by means of block-online beamforming that recursively updates the signal statistics. Experimental results show that the additional spatial information clearly improves source extraction, in particular in the same-gender case, and that our proposal achieves state-of-the-art performance in terms of distortion reduction and recognition accuracy.


Visualization of Marangoni Phenomena during Droplet Formation

J. Heine, C. Wecker, E. Kenig, H. Bart. Visualization of Marangoni Phenomena during Droplet Formation. 2019.


Methode zur Erfassung von Stofftransport an fluiden Phasengrenzflächen

A. Schulz, C. Wecker, E. Kenig, Chemie Ingenieur Technik (2019)

DOI


Ballistic photocurrents in semiconductor quantum wells caused by the excitation of asymmetric excitons

H.T. Duc, C. Ngo, T. Meier, Physical Review B (2019), 100(4)

DOI


Split-ring polariton condensates as macroscopic two-level quantum systems

Y. Xue, I. Chestnov, E. Sedov, S. Schumacher, X. Ma, A. Kavokin, in: arXiv:1907.00383, 2019

Superposition states of circular currents of exciton-polaritons mimic the superconducting flux qubits. The current states are formed by a macroscopic number of bosonic quasiparticles that compose a single quantum state of a many-body condensate. The essential difference between a polariton fluid and a superconducting current comes from the fact that in contrast to Cooper pairs polaritons are electrically neutral, and the magnetic field would not have a significant effect on a polariton flow. Nevertheless, the phase of a polariton condensate must change by an integer number of 2$\pi$, when going around the ring. If one introduces a $\pi$-phase delay line in the ring, the system is obliged to propagate a clockwise or anticlockwise circular current to reduce the total phase gained over one round-trip to zero or to build it up to $2\pi$. We show that such a $\pi$-delay line can be provided by a dark soliton embedded into a ring condensate and pinned to a potential well created by a C-shape non-resonant pump-spot. The physics of resulting split-ring polariton condensates is essentially similar to the physics of flux qubits. In particular, they exhibit pronounced coherent oscillations passing periodically through clockwise and anticlockwise current states. We predict that these oscillations may persist far beyond the coherence time of polariton condensates. As a consequence, the qubits based on split-ring polariton condensates are expected to possess very high figures of merit that makes them a valuable alternative to superconducting qubits.


Experimental and Theoretical High Energy Resolution Hard X-ray Absorption and Emission Spectroscopy on Biomimetic Cu2S2 Complexes

P. Müller, A. Neuba, U. Flörke, G. Henkel, T.D. Kühne, M. Bauer, The Journal of Physical Chemistry A (2019), 123(16), pp. 3575-3581

DOI


Proton Irradiation Induced Defects in β-Ga2O3: A Combined EPR and Theory Study

H.J. von Bardeleben, S. Zhou, U. Gerstmann, D. Skachkov, W.R.L. Lambrecht, Q.D. Ho, P. Deák, APL Materials (2019), 7

DOI


Potassium titanyl phosphate (KTP) quasiparticle energies and optical response

S. Neufeld, A. Bocchini, U. Gerstmann, A. Schindlmayr, W.G. Schmidt, Journal of Physics: Materials (2019)

DOI


Unsupervised training of neural mask-based beamforming

L. Drude, J. Heymann, R. Haeb-Umbach, in: INTERSPEECH 2019, Graz, Austria, 2019

We present an unsupervised training approach for a neural network-based mask estimator in an acoustic beamforming application. The network is trained to maximize a likelihood criterion derived from a spatial mixture model of the observations. It is trained from scratch without requiring any parallel data consisting of degraded input and clean training targets. Thus, training can be carried out on real recordings of noisy speech rather than simulated ones. In contrast to previous work on unsupervised training of neural mask estimators, our approach avoids the need for a possibly pre-trained teacher model entirely. We demonstrate the effectiveness of our approach by speech recognition experiments on two different datasets: one mainly deteriorated by noise (CHiME 4) and one by reverberation (REVERB). The results show that the performance of the proposed system is on par with a supervised system using oracle target masks for training and with a system trained using a model-based teacher.


Numerical Simulation of Forced Convection in a Microchannel with Realistic Roughness of 3D Printed Surface

S.A. Manavi, E. Kenig, in: Computer Aided Chemical Engineering, 29th European Symposium on Computer Aided Process Engineering, 2019

DOI


In-situ Messung des Stofftransports bei der Tropfenbildung

J. Heine, C. Wecker, E. Kenig, H. Bart. In-situ Messung des Stofftransports bei der Tropfenbildung. 2019.


2018

Identifying On-Surface Site-Selective Chemical Conversions by Theory-Aided NEXAFS Spectroscopy: The Case of Free-Base Corroles on Ag(111)

H. Aldahhak, M. Paszkiewicz, E. Rauls, F. Allegretti, S. Tebi, A.C. Papageorgiou, Y. Zhang, L. Zhang, T. Lin, T. Paintner, R. Koch, W.G. Schmidt, J.V. Barth, W. Schöfberger, S. Müllegger, F. Klappenberger, U. Gerstmann, Chemistry - A European Journal (2018), pp. 6787-6797

DOI


Front-End Processing for the CHiME-5 Dinner Party Scenario

C. Boeddeker, J. Heitkaemper, J. Schmalenstroeer, L. Drude, J. Heymann, R. Haeb-Umbach, in: INTERSPEECH 2018, Hyderabad, India, 2018

This contribution presents a speech enhancement system for the CHiME-5 Dinner Party Scenario. The front-end employs multi-channel linear time-variant filtering and achieves its gains without the use of a neural network. We present an adaptation of blind source separation techniques to the CHiME-5 database which we call Guided Source Separation (GSS). Using the baseline acoustic and language model, the combination of Weighted Prediction Error based dereverberation, guided source separation, and beamforming reduces the WER by 10:54% (relative) for the single array track and by 21:12% (relative) on the multiple array track.


Integration neural network based beamforming and weighted prediction error dereverberation

L. Drude, C. Boeddeker, J. Heymann, K. Kinoshita, M. Delcroix, T. Nakatani, R. Haeb-Umbach, in: INTERSPEECH 2018, Hyderabad, India, 2018

The weighted prediction error (WPE) algorithm has proven to be a very successful dereverberation method for the REVERB challenge. Likewise, neural network based mask estimation for beamforming demonstrated very good noise suppression in the CHiME 3 and CHiME 4 challenges. Recently, it has been shown that this estimator can also be trained to perform dereverberation and denoising jointly. However, up to now a comparison of a neural beamformer and WPE is still missing, so is an investigation into a combination of the two. Therefore, we here provide an extensive evaluation of both and consequently propose variants to integrate deep neural network based beamforming with WPE. For these integrated variants we identify a consistent word error rate (WER) reduction on two distinct databases. In particular, our study shows that deep learning based beamforming benefits from a model-based dereverberation technique (i.e. WPE) and vice versa. Our key findings are: (a) Neural beamforming yields the lower WERs in comparison to WPE the more channels and noise are present. (b) Integration of WPE and a neural beamformer consistently outperforms all stand-alone systems.


Guided ultrasonic waves for determining effective orthotropic material parameters of continuous-fiber reinforced thermoplastic plates

M. Webersen, S. Johannesmann, J. Düchting, L. Claes, B. Henning, Ultrasonics (2018), 84, pp. 53-62

DOI


Einfluss mechanischer Vorspannung auf das mechanische Materialverhalten von Polymeren

M. Webersen, S. Johannesmann, T. Brockschmidt, F. Rump, L. Claes, B. Henning, 2018


Impact of finite-temperature and condensed-phase effects on theoretical X-ray absorption spectra of transition metal complexes

P. Müller, K. Karhan, M. Krack, U. Gerstmann, W.G. Schmidt, M. Bauer, T.D. Kühne, Journal of Computational Chemistry (2018), pp. 712-716

DOI


Database screening of ternary chalcogenides for p-type transparent conductors

R. Kormath Madam Raghupathy, H. Wiebeler, T.D. Kühne, C. Felser, H. Mirhosseini, Chemistry of Materials (2018), 30(19), pp. 6794-6800

DOI


Electron Paramagnetic Resonance Tagged High-Resolution Excitation Spectroscopy of NV-Centers in 4H-SiC

S.A. Zargaleh, H.J. von Bardeleben, J.L. Cantin, U. Gerstmann, S. Hameau, B. Ebl\'e, W. Gao, Phys. Rev. B (2018), 98(21), pp. 214113

DOI


NARA-WPE: A Python package for weighted prediction error dereverberation in Numpy and Tensorflow for online and offline processing

L. Drude, J. Heymann, C. Boeddeker, R. Haeb-Umbach, in: ITG 2018, Oldenburg, Germany, 2018

NARA-WPE is a Python software package providing implementations of the weighted prediction error (WPE) dereverberation algorithm. WPE has been shown to be a highly effective tool for speech dereverberation, thus improving the perceptual quality of the signal and improving the recognition performance of downstream automatic speech recognition (ASR). It is suitable both for single-channel and multi-channel applications. The package consist of (1) a Numpy implementation which can easily be integrated into a custom Python toolchain, and (2) a TensorFlow implementation which allows integration into larger computational graphs and enables backpropagation through WPE to train more advanced front-ends. This package comprises of an iterative offline (batch) version, a block-online version, and a frame-online version which can be used in moderately low latency applications, e.g. digital speech assistants.


CIRCA: Towards a Modular and Extensible Framework for Approximate Circuit Generation

L.M. Witschen, T. Wiersema, H. Ghasemzadeh Mohammadi, M. Awais, M. Platzner, in: Third Workshop on Approximate Computing (AxC 2018), 2018

Existing approaches and tools for the generation of approximate circuits often lack generality and are restricted to certain circuit types, approximation techniques, and quality assurance methods. Moreover, only few tools are publicly available. This hinders the development and evaluation of new techniques for approximating circuits and their comparison to previous approaches. In this paper, we first analyze and classify related approaches and then present CIRCA, our flexible framework for search-based approximate circuit generation. CIRCA is developed with a focus on modularity and extensibility. We present the architecture of CIRCA with its clear separation into stages and functional blocks, report on the current prototype, and show initial experiments.


Akustische Charakterisierung der richtungsabhängigen elastischen Eigenschaften faserverstärkter Kunststoffe

M. Webersen, S. Johannesmann, J. Düchting, L. Claes, B. Henning, in: Fortschritte der Akustik - DAGA 2018, 2018, pp. 1263-1266


Vortex Multistability and Bessel Vortices in Polariton Condensates

X. Ma, S. Schumacher, Physical Review Letters (2018), 121(22)

DOI


Theoretical Investigation of Interaction of CuInSe2 Absorber Material with Oxygen, Hydrogen, and Water

S. Sahoo, R. Kormath Madam Raghupathy, T.D. Kühne, H. Mirhosseini, J. Phys. Chem. C (2018), 122(37), pp. 21202-21209

DOI


Plasmon spectroscopy: Robust metallicity of Au wires on Si(557) upon oxidation

Z. Mamiyev, T. Lichtenstein, C. Tegenkamp, C. Braun, W.G. Schmidt, S. Sanna, H. Pfnür, Physical Review Materials (2018), 2(6)

DOI


Temperature stabilizes rough Au/Ge(001) surface reconstructions

K. Seino, S. Sanna, W.G. Schmidt, Surface Science (2018), 667, pp. 101-104

DOI


Unraveling the Oxidation and Spin State of Mn–Corrole through X-ray Spectroscopy and Quantum Chemical Analysis

M. Paszkiewicz, T. Biktagirov, H. Aldahhak, F. Allegretti, E. Rauls, W. Schöfberger, W.G. Schmidt, J.V. Barth, U. Gerstmann, F. Klappenberger, The Journal of Physical Chemistry Letters (2018), pp. 6412-6420

DOI


An acoustic waveguide-based approach to the complete characterisation of linear elastic, orthotropic material behaviour

S. Johannesmann, J. Düchting, M. Webersen, L. Claes, B. Henning, tm - Technisches Messen (2018), 2018(85), pp. 478-486

DOI


Using Approximate Computing for the Calculation of Inverse Matrix p-th Roots

M. Lass, T. Kühne, C. Plessl, Embedded Systems Letters (2018), 10(2), pp. 33-36

Approximate computing has shown to provide new ways to improve performance and power consumption of error-resilient applications. While many of these applications can be found in image processing, data classification or machine learning, we demonstrate its suitability to a problem from scientific computing. Utilizing the self-correcting behavior of iterative algorithms, we show that approximate computing can be applied to the calculation of inverse matrix p-th roots which are required in many applications in scientific computing. Results show great opportunities to reduce the computational effort and bandwidth required for the execution of the discussed algorithm, especially when targeting special accelerator hardware.


Observation and Uses of Position-Space Bloch Oscillations in an Ultracold Gas

Z.A. Geiger, K.M. Fujiwara, K. Singh, R. Senaratne, S.V. Rajagopal, M. Lipatov, T. Shimasaki, R. Driben, V.V. Konotop, T. Meier, D.M. Weld, Physical Review Letters (2018), 120(21)

DOI


Structural dynamics upon photoexcitation-induced charge transfer in a dicopper(i)–disulfide complex

M. Naumova, D. Khakhulin, M. Rebarz, M. Rohrmüller, B. Dicke, M. Biednov, A. Britz, S. Espinoza, B. Grimm-Lebsanft, M. Kloz, N. Kretzschmar, A. Neuba, J. Ortmeyer, R. Schoch, J. Andreasson, M. Bauer, C. Bressler, W.G. Schmidt, G. Henkel, M. Rübhausen, Physical Chemistry Chemical Physics (2018), pp. 6274-6286

<p>A study of structural evolution upon photoinduced charge transfer in a dicopper complex with biologically relevant sulfur coordination.</p>


Liner Shipping Single Service Design Problem with Arrival Time Service Levels

K. Tierney, J.F. Ehmke, A.M. Campbell, D. Müller, Flexible Services and Manufacturing Journal (2018), pp. 620-652

DOI


Microscopic theory of cavity-enhanced single-photon emission from optical two-photon Raman processes

D. Breddermann, T. Praschan, D. Heinze, R. Binder, S. Schumacher, Physical Review B (2018), 97(12)

DOI


Solving Maxwell's Equations with Modern C++ and SYCL: A Case Study

A. Afzal, C. Schmitt, S. Alhaddad, Y. Grynko, J. Teich, J. Förstner, F. Hannig, in: Proceedings of the 29th Annual IEEE International Conference on Application-specific Systems, Architectures and Processors (ASAP), 2018, pp. 49-56

In scientific computing, unstructured meshes are a crucial foundation for the simulation of real-world physical phenomena. Compared to regular grids, they allow resembling the computational domain with a much higher accuracy, which in turn leads to more efficient computations.<br />There exists a wealth of supporting libraries and frameworks that aid programmers with the implementation of applications working on such grids, each built on top of existing parallelization technologies. However, many approaches require the programmer to introduce a different programming paradigm into their application or provide different variants of the code. SYCL is a new programming standard providing a remedy to this dilemma by building on standard C ++17 with its so-called single-source approach: Programmers write standard C ++ code and expose parallelism using C++17 keywords. The application is<br />then transformed into a concrete implementation by the SYCL implementation. By encapsulating the OpenCL ecosystem, different SYCL implementations enable not only the programming of CPUs but also of heterogeneous platforms such as GPUs or other devices. For the first time, this paper showcases a SYCL-<br />based solver for the nodal Discontinuous Galerkin method for Maxwell’s equations on unstructured meshes. We compare our solution to a previous C-based implementation with respect to programmability and performance on heterogeneous platforms.<br


Application of the Discontinuous Galerkin Time Domain Method in Nonlinear Nanoplasmonics

Y. Grynko, J. Förstner, in: 2018 IEEE 17th International Conference on Mathematical Methods in Electromagnetic Theory (MMET), IEEE, 2018

DOI


Electric Field Induced Raman Scattering at the Sb-InP(110) Interface: The Surface Dipole Contribution

N. Esser, W.G. Schmidt, physica status solidi (b) (2018)

DOI


Acoustic material characterization of prestressed, plate-shaped specimens

S. Johannesmann, T. Brockschmidt, F. Rump, M. Webersen, L. Claes, B. Henning, in: Sensoren und Messsysteme, VDE Verlag GmbH, 2018, pp. 231-234


Next Generation of Guanidine Quinoline Copper Complexes for Highly Controlled ATRP: Influence of Backbone Substitution on Redox Chemistry and Solubility

T. Rösener, A. Hoffmann, S. Herres-Pawlis, European Journal of Inorganic Chemistry (2018), 2018(27), pp. 3164-3175

Ligands DMEG6etqu, TMG6etqu, DMEG6buqu, and TMG6buqu were developed on the basis of guanidine quinoline (GUAqu) ligands 1,3-dimethyl-N-(quinolin-8-yl)imidazolidin-2-imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quinolin-8-yl)guanidine (TMGqu). These ligands feature an alkyl substituent at the C6 of the quinoline backbone. The synthetic strategy developed here enables inexpensive syntheses of any kind of C6-substituted GUAqu ligands. On one hand, the alkylation increases the solubility of corresponding copper complexes in apolar atom transfer radical polymerization (ATRP) monomers like styrene. On the other hand, it has a significant electronic influence and thus an effect on the donor properties of the new ligands. Seven CuI and CuII complexes of DMEG6etqu and TMG6etqu have been crystallized and were studied with regard to their structural and electrochemical properties. CuI and CuII complexes of DMEG6buqu and TMG6buqu turned out to be perfectly soluble in pure styrene even at room temperature, which makes them excellent catalysts in the ATRP of apolar monomers. The key characteristics of the ATRP equilibrium, KATRP and kact, were determined for the new complexes. In addition, we used our recently developed DFT methodology, NBO analysis, and isodesmic reactions to predict the influence of the introduced alkyl substituents. It turned out that high conformational freedom in the complex structures leads to a significant uncertainty in prediction of the thermodynamic properties.


Self-configuring Cost-Sensitive Hierarchical Clustering with Recourse

C. Ansotegui, M. Sellmann, K. Tierney, in: Principles and Practice of Constraint Programming, Springer International Publishing, 2018, pp. 524-534

We revisit algorithm selection for declarative programming solvers. We introduce two main ideas to improve cost-sensitive hierarchical clustering: First, to augment the portfolio builder with a self-configuration component. And second, we propose that the algorithm selector assesses the confidence level of its own prediction, so that a more defensive recourse action can be used to overturn the original recommendation.


Nonlinearity-induced localization in a periodically driven semidiscrete system

R. Driben, V.V. Konotop, B.A. Malomed, T. Meier, A.V. Yulin, Physical Review E (2018), 97(6)

DOI


Polytypism driven zero-field splitting of silicon vacancies in 6H-SiC

T. Biktagirov, W.G. Schmidt, U. Gerstmann, B. Yavkin, S. Orlinskii, P. Baranov, V. Dyakonov, V. Soltamov, Physical Review B (2018), 98(19)

DOI


Liquid State Isomorphism, Rosenfeld-Tarazona Temperature Scaling, and Riemannian Thermodynamic Geometry

P. Mausbach, A. Köster, J. Vrabec, Phys. Rev. E (2018), 97(5), pp. 052149

DOI


Solving Real-World Sized Container Pre-Marshalling Problems with an Iterative Deepening Branch-and-Bound Algorithm

S. Tanaka, K. Tierney, European Journal of Operational Research (2018), 264(1), pp. 165 - 180

DOI


Imaging of 180∘ ferroelectric domain walls in uniaxial ferroelectrics by confocal Raman spectroscopy: Unraveling the contrast mechanism

M. Rüsing, S. Neufeld, J. Brockmeier, C. Eigner, P. Mackwitz, K. Spychala, C. Silberhorn, W.G. Schmidt, G. Berth, A. Zrenner, S. Sanna, Physical Review Materials (2018)

DOI


Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)]

M. Friedrich, W.G. Schmidt, A. Schindlmayr, S. Sanna, Physical Review Materials (2018), 2(1)

DOI


Probing quasi-one-dimensional band structures by plasmon spectroscopy

T. Lichtenstein, Z. Mamiyev, C. Braun, S. Sanna, W.G. Schmidt, C. Tegenkamp, H. Pfnür, Physical Review B (2018), 97(16)

DOI


Beyond the molecular movie: Dynamics of bands and bonds during a photoinduced phase transition

C.W. Nicholson, A. Lücke, W.G. Schmidt, M. Puppin, L. Rettig, R. Ernstorfer, M. Wolf, Science (2018), pp. 821-825

<jats:p>Ultrafast nonequilibrium dynamics offer a route to study the microscopic interactions that govern macroscopic behavior. In particular, photoinduced phase transitions (PIPTs) in solids provide a test case for how forces, and the resulting atomic motion along a reaction coordinate, originate from a nonequilibrium population of excited electronic states. Using femtosecond photoemission, we obtain access to the transient electronic structure during an ultrafast PIPT in a model system: indium nanowires on a silicon(111) surface. We uncover a detailed reaction pathway, allowing a direct comparison with the dynamics predicted by ab initio simulations. This further reveals the crucial role played by localized photoholes in shaping the potential energy landscape and enables a combined momentum- and real-space description of PIPTs, including the ultrafast formation of chemical bonds.</jats:p>


A Massively Parallel Algorithm for the Approximate Calculation of Inverse p-th Roots of Large Sparse Matrices

M. Lass, S. Mohr, H. Wiebeler, T. Kühne, C. Plessl, in: Proc. Platform for Advanced Scientific Computing (PASC) Conference, ACM, 2018

We present the submatrix method, a highly parallelizable method for the approximate calculation of inverse p-th roots of large sparse symmetric matrices which are required in different scientific applications. Following the idea of Approximate Computing, we allow imprecision in the final result in order to utilize the sparsity of the input matrix and to allow massively parallel execution. For an n x n matrix, the proposed algorithm allows to distribute the calculations over n nodes with only little communication overhead. The result matrix exhibits the same sparsity pattern as the input matrix, allowing for efficient reuse of allocated data structures. We evaluate the algorithm with respect to the error that it introduces into calculated results, as well as its performance and scalability. We demonstrate that the error is relatively limited for well-conditioned matrices and that results are still valuable for error-resilient applications like preconditioning even for ill-conditioned matrices. We discuss the execution time and scaling of the algorithm on a theoretical level and present a distributed implementation of the algorithm using MPI and OpenMP. We demonstrate the scalability of this implementation by running it on a high-performance compute cluster comprised of 1024 CPU cores, showing a speedup of 665x compared to single-threaded execution.


Making the Case for Proof-carrying Approximate Circuits

L.M. Witschen, T. Wiersema, M. Platzner, in: 4th Workshop On Approximate Computing (WAPCO 2018), 2018


Probing quasi-one-dimensional band structures by plasmon spectroscopy

T. Lichtenstein, Z. Mamiyev, C. Braun, S. Sanna, W.G. Schmidt, C. Tegenkamp, H. Pfnür, Physical Review B (2018), 97(16)

DOI


Spin pairing versus spin chains at Si(553)-Au surfaces

C. Braun, U. Gerstmann, W.G. Schmidt, Physical Review B (2018), 98(12)

DOI


Vibrational properties of the Au-(3×3)/Si(111) surface reconstruction

B. Halbig, M. Liebhaber, U. Bass, J. Geurts, E. Speiser, J. Räthel, S. Chandola, N. Esser, M. Krenz, S. Neufeld, W.G. Schmidt, S. Sanna, Physical Review B (2018), 97(3)

DOI


Calculation of spin-spin zero-field splitting within periodic boundary conditions: Towards all-electron accuracy

T. Biktagirov, W.G. Schmidt, U. Gerstmann, Physical Review B (2018), 97(11)

DOI


Signatures of transient Wannier-Stark localization in bulk gallium arsenide

C. Schmidt, J. Bühler, A. Heinrich, J. Allerbeck, R. Podzimski, D. Berghoff, T. Meier, W.G. Schmidt, C. Reichl, W. Wegscheider, D. Brida, A. Leitenstorfer, Nature Communications (2018), 9, pp. 2890

DOI


Tuning Stochastic Space Compaction to Faster-than-at-Speed Test

A. Sprenger, S. Hellebrand, in: 2018 IEEE 21st International Symposium on Design and Diagnostics of Electronic Circuits & Systems (DDECS), IEEE, 2018

DOI


2017


Reactive Dialectic Search Portfolios for MaxSAT.

C. Ansotegui, J. Pon, M. Sellmann, K. Tierney, in: AAAI, 2017, pp. 765-772


Bloch oscillations and resonant radiation of light propagating in arrays of nonlinear fibers with high-order dispersion

A. Yulin, R. Driben, T. Meier, Physical Review A (2017), 96(3)

DOI


Optically Controlled Orbital Angular Momentum Generation in a Polaritonic Quantum Fluid

S. Luk, N. Kwong, P. Lewandowski, S. Schumacher, R. Binder, Physical Review Letters (2017), 119(11)

DOI


Controlling the optical spin Hall effect with light

O. Lafont, S.M.H. Luk, P. Lewandowski, N.H. Kwong, P.T. Leung, E. Galopin, A. Lemaitre, J. Tignon, S. Schumacher, E. Baudin, R. Binder, Applied Physics Letters (2017)

DOI


Creation and Manipulation of Stable Dark Solitons and Vortices in Microcavity Polariton Condensates

X. Ma, O.A. Egorov, S. Schumacher, Physical Review Letters (2017), 118(15)

DOI


New pyridinium based ionic dyes for the hydrogen evolution reaction

D.D. Konieczna, H. Biller, M. Witte, W.G. Schmidt, A. Neuba, R. Wilhelm, Tetrahedron (2017), pp. 142-149

DOI


High-pressure hydrogen sulfide by diffusion quantum Monte Carlo

.S.. Azadi, T.D. Kühne, The Journal of Chemical Physics (2017), 146(8), pp. 084503

DOI


Premelting, Solid-Fluid Equilibria, and Thermodynamic Properties in the High Density Region Based on the Lennard-Jones Potential

A. Köster, P. Mausbach, J. Vrabec, The Journal of Chemical Physics (2017), 147(14), pp. 144502

DOI


Efficient PAW-based bond strength analysis for understanding the In/Si(111)(8 × 2) - (4 × 1) phase transition

A. Lücke, U. Gerstmann, T.D. Kühne, W.G. Schmidt, Journal of Computational Chemistry (2017), pp. 2276-2282

DOI


Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory

M. Friedrich, W.G. Schmidt, A. Schindlmayr, S. Sanna, Physical Review Materials (2017)

DOI


X-ray Spectroscopy of Thin Film Free-Base Corroles: A Combined Theoretical and Experimental Characterization

H. Aldahhak, M. Paszkiewicz, F. Allegretti, D.A. Duncan, S. Tebi, P.S. Deimel, P. Casado Aguilar, Y. Zhang, A.C. Papageorgiou, R. Koch, J.V. Barth, W.G. Schmidt, S. Müllegger, W. Schöfberger, F. Klappenberger, E. Rauls, U. Gerstmann, The Journal of Physical Chemistry C (2017), 121, pp. 2192-2200

DOI


Flexible FPGA design for FDTD using OpenCL

T. Kenter, J. Förstner, C. Plessl, in: Proc. Int. Conf. on Field Programmable Logic and Applications (FPL), IEEE, 2017

DOI


BEAMNET: End-to-End Training of a Beamformer-Supported Multi-Channel ASR System

J. Heymann, L. Drude, C. Boeddeker, P. Hanebrink, R. Haeb-Umbach, in: Proc. IEEE Intl. Conf. on Acoustics, Speech and Signal Processing (ICASSP), 2017

This paper presents an end-to-end training approach for a beamformer-supported multi-channel ASR system. A neural network which estimates masks for a statistically optimum beamformer is jointly trained with a network for acoustic modeling. To update its parameters, we propagate the gradients from the acoustic model all the way through feature extraction and the complex valued beamforming operation. Besides avoiding a mismatch between the front-end and the back-end, this approach also eliminates the need for stereo data, i.e., the parallel availability of clean and noisy versions of the signals. Instead, it can be trained with real noisy multichannel data only. Also, relying on the signal statistics for beamforming, the approach makes no assumptions on the configuration of the microphone array. We further observe a performance gain through joint training in terms of word error rate in an evaluation of the system on the CHiME 4 dataset.


Comprehensive Assessment of COSMO-SAC Models for Predictions of Fluid-Phase Equilibria

R. Fingerhut, W. Chen, A. Schedemann, W. Cordes, J. Rarey, C. Hsieh, J. Vrabec, S. Lin, Industrial & Engineering Chemistry Research (2017), 56(35), pp. 9868-9884

DOI


Understanding the Differing Fluid Phase Behavior of Cyclohexane + Benzene and Their Hydroxylated or Aminated Forms

Y.M. Muñoz-Muñoz, C. Hsieh, J. Vrabec, The Journal of Physical Chemistry B (2017), 121(21), pp. 5374-5384

DOI


Theory of optically controlled anisotropic polariton transport in semiconductor double microcavities

S.M.H. Luk, P. Lewandowski, N.H. Kwong, E. Baudin, O. Lafont, J. Tignon, P.T. Leung, C.K.P. Chan, M. Babilon, S. Schumacher, R. Binder, Journal of the Optical Society of America B (2017), 35(1)

DOI


H+CH4→H2+CH3 Initial State-Selected Reaction Probabilities on Different Potential Energy Surfaces

R. Ellerbrock, U. Manthe, Chemical Physics (2017), 482, pp. 106 - 112

Initial state-selected reaction probabilities for the H+CH4→H2+CH3 reaction on a recently developed potential energy surface which employs neutral network fitting based on permutational invariant polynomials are reported. The quantum dynamics calculations use the quantum transition state concept and the multi-layer multi-configurational time-dependent Hartree approach and study the reaction process in full-dimensionality for vanishing total angular momentum. A detailed comparison with previous results obtained on other high-level potential energy surfaces is given. The connection between the level of quantum state resolution and the sensitivity of the results on differences in the potential energy surfaces is highlighted. Employing a decomposition of the total reactivity into contributions of the different vibrational states of the activated complex, it is found that differences between the potential energy surfaces are mainly related to the umbrella motion of the methyl group.


Zn–VI quasiparticle gaps and optical spectra from many-body calculations

A. Riefer, N. Weber, J. Mund, D.R. Yakovlev, M. Bayer, A. Schindlmayr, C. Meier, W.G. Schmidt, Journal of Physics: Condensed Matter (2017)

DOI


Current density analysis of electron transport through molecular wires in open quantum systems

D. Nozaki, W.G. Schmidt, Journal of Computational Chemistry (2017), 38, pp. 1685-1692

DOI


Electron paramagnetic resonance calculations for hydrogenated Si surfaces

M. Rohrmüller, W.G. Schmidt, U. Gerstmann, Physical Review B (2017), 95(12)

DOI


LiNbO3 surfaces from a microscopic perspective

S. Sanna, W.G. Schmidt, Journal of Physics: Condensed Matter (2017)

DOI


Efficient Branch and Bound on FPGAs Using Work Stealing and Instance-Specific Designs

H. Riebler, M. Lass, R. Mittendorf, T. Löcke, C. Plessl, ACM Transactions on Reconfigurable Technology and Systems (TRETS) (2017), 10(3), pp. 24:1-24:23

Branch and bound (B&B) algorithms structure the search space as a tree and eliminate infeasible solutions early by pruning subtrees that cannot lead to a valid or optimal solution. Custom hardware designs significantly accelerate the execution of these algorithms. In this article, we demonstrate a high-performance B&B implementation on FPGAs. First, we identify general elements of B&B algorithms and describe their implementation as a finite state machine. Then, we introduce workers that autonomously cooperate using work stealing to allow parallel execution and full utilization of the target FPGA. Finally, we explore advantages of instance-specific designs that target a specific problem instance to improve performance. We evaluate our concepts by applying them to a branch and bound problem, the reconstruction of corrupted AES keys obtained from cold-boot attacks. The evaluation shows that our work stealing approach is scalable with the available resources and provides speedups proportional to the number of workers. Instance-specific designs allow us to achieve an overall speedup of 47 × compared to the fastest implementation of AES key reconstruction so far. Finally, we demonstrate how instance-specific designs can be generated just-in-time such that the provided speedups outweigh the additional time required for design synthesis.


Proof-Carrying Hardware via Inductive Invariants

T. Isenberg, M. Platzner, H. Wehrheim, T. Wiersema, ACM Transactions on Design Automation of Electronic Systems (2017)(4), pp. 61:1--61:23

Proof-carrying hardware (PCH) is a principle for achieving safety for dynamically reconfigurable hardware systems. The producer of a hardware module spends huge effort when creating a proof for a safety policy. The proof is then transferred as a certificate together with the configuration bitstream to the consumer of the hardware module, who can quickly verify the given proof. Previous work utilized SAT solvers and resolution traces to set up a PCH technology and corresponding tool flows. In this article, we present a novel technology for PCH based on inductive invariants. For sequential circuits, our approach is fundamentally stronger than the previous SAT-based one since we avoid the limitations of bounded unrolling. We contrast our technology to existing ones and show that it fits into previously proposed tool flows. We conduct experiments with four categories of benchmark circuits and report consumer and producer runtime and peak memory consumption, as well as the size of the certificates and the distribution of the workload between producer and consumer. Experiments clearly show that our new induction-based technology is superior for sequential circuits, whereas the previous SAT-based technology is the better choice for combinational circuits.


Round Robin Study: Molecular Simulation of Thermodynamic Properties from Models with Internal Degrees of Freedom

M. Schappals, A. Mecklenfeld, L. Kröger, V. Botan, A. Köster, S. Stephan, E.J. García, G. Rutkai, G. Raabe, P. Klein, K. Leonhard, C.W. Glass, J. Lenhard, J. Vrabec, H. Hasse, Journal of Chemical Theory and Computation (2017), 13(9), pp. 4270-4280

DOI


Anisotropic excitons and their contributions to shift current transients in bulk GaAs

R. Podzimski, H.T. Duc, T. Meier, Physical Review B (2017), 96(20)

DOI


Vortex-vortex control in exciton-polariton condensates

X. Ma, S. Schumacher, Physical Review B (2017), 95(23)

DOI


How Well Does the Lennard-Jones Potential Represent the Thermodynamic Properties of Noble Gases?

G. Rutkai, M. Thol, R. Span, J. Vrabec, Molecular Physics (2017), 115(9-12), pp. 1104-1121

DOI


Geometrically Disordered Network Models, Quenched Quantum Gravity, and Critical Behavior at Quantum Hall Plateau Transitions

I. Gruzberg, A. Klümper, W. Nuding, A. Sedrakyan, Phys. Rev. B (2017), 95, pp. 125414

DOI


Optically excited structural transition in atomic wires on surfaces at the quantum limit

T. Frigge, B. Hafke, T. Witte, B. Krenzer, C. Streubühr, A. Samad Syed, V. Mikšić Trontl, I. Avigo, P. Zhou, M. Ligges, D. von der Linde, U. Bovensiepen, M. Horn-von Hoegen, S. Wippermann, A. Lücke, S. Sanna, U. Gerstmann, W.G. Schmidt, Nature (2017), 544, pp. 207-211

DOI


Tuning the conductivity along atomic chains by selective chemisorption

F. Edler, I. Miccoli, J.P. Stöckmann, H. Pfnür, C. Braun, S. Neufeld, S. Sanna, W.G. Schmidt, C. Tegenkamp, Physical Review B (2017), 95(12)

DOI


Understanding band alignments in semiconductor heterostructures: Composition dependence and type-I–type-II transition of natural band offsets in nonpolar zinc-blendeAlxGa1−xN/AlyGa1−yNcomposites

M. Landmann, E. Rauls, W.G. Schmidt, Physical Review B (2017), 95(15)

DOI


Solving the Bethe-Salpeter equation for the second-harmonic generation in Zn chalcogenides

A. Riefer, W.G. Schmidt, Physical Review B (2017), 96(23)

DOI


Simulation of Second Harmonic Generation from Photonic Nanostructures Using the Discontinuous Galerkin Time Domain Method

Y. Grynko, J. Förstner, in: Recent Trends in Computational Photonics, Springer International Publishing, 2017, pp. 261-284

We apply the Discontinuous Galerkin Time Domain (DGTD) method for numerical simulations of the second harmonic generation from various metallic nanostructures. A Maxwell–Vlasov hydrodynamic model is used to describe the nonlinear effects in the motion of the excited free electrons in a metal. The results are compared with the corresponding experimental measurements for split-ring resonators and plasmonic gap antennas.


Ultrasonic measurements in the characterization of viscoelasticity and aging of polymers

F. Bause, L. Claes, M. Webersen, B. Henning, in: PROCEEDINGS -- AMA Conferences 2017, 2017, pp. 414

DOI


Optical switching of polariton density patterns in a semiconductor microcavity

N.H. Kwong, C.Y. Tsang, S.M.H. Luk, Y.C. Tse, C.K.P. Chan, P. Lewandowski, P.T. Leung, S. Schumacher, R. Binder, Physica Scripta (2017)

DOI


Molecular Orbital Rule for Quantum Interference in Weakly Coupled Dimers: Low-Energy Giant Conductivity Switching Induced by Orbital Level Crossing

D. Nozaki, A. Lücke, W.G. Schmidt, The Journal of Physical Chemistry Letters (2017), pp. 727-732

DOI


[Cu6(NGuaS)6]2+ and its oxidized and reduced derivatives: Confining electrons on a torus

M. Witte, M. Rohrmüller, U. Gerstmann, G. Henkel, W.G. Schmidt, S. Herres-Pawlis, Journal of Computational Chemistry (2017), pp. 1752-1761

DOI


Si(775)-Au atomic chains: Geometry, optical properties, and spin order

C. Braun, C. Hogan, S. Chandola, N. Esser, S. Sanna, W.G. Schmidt, Physical Review Materials (2017), 1(5)

DOI


A Framework for the Synthesis of Approximate Circuits

L.M. Witschen, Master's thesis, Paderborn University, 2017


Understanding band alignments in semiconductor heterostructures: Composition dependence and type-I–type-II transition of natural band offsets in nonpolar zinc-blendeAlxGa1−xN/AlyGa1−yNcomposites

M. Landmann, E. Rauls, W.G. Schmidt, Physical Review B (2017)

DOI


Viskoelastizität und Anisotropie von Kunststoffen: Ultraschallbasierte Methoden zur Materialparameterbestimmung

F. Bause, L. Claes, M. Webersen, S. Johannesmann, B. Henning, tm - Technisches Messen (2017), 84(3)

DOI


Integrating Fleet Deployment into the Liner Shipping Cargo Allocation Problem

D. Müller, S. Guericke, K. Tierney, in: Computational Logistics, Springer International Publishing, 2017, pp. 306-320

Liner carriers change their network on a regular basis, and they are therefore interested in a practical evaluation of the impact these changes have on the cargo flows in their networks. Despite great advancements in the practical applicability of network evaluators in recent years, vessel deployment continues to be considered as an input into the problem, rather than a decision. In this paper, we propose an extension of a state-of-the-art mixed integer programming model for the LSCAP that incorporates the optimization of vessel count and vessel classes for each service. We perform a computational analysis on liner shipping networks of different sizes and compare our optimized results to fixed deployment scenarios. By integrating fleet deployment decisions into the cargo allocation problem, liner carriers can increase the profitability of their networks by at least 2.8 to 16.9{\%} and greatly enhance their decision making.


Detection of Copper Bisguanidine NO Adducts by UV-vis Spectroscopy and a SuperFocus Mixer

A. Oppermann, L. Laurini, F. Etscheidt, K. Hollmann, F. Strassl, A. Hoffmann, D. Schurr, R. Dittmeyer, G. Rinke, S. Herres-Pawlis, Chemical Engineering \& Technology (2017), 40(8), pp. 1475-1483

Abstract The reaction of Cu(I) bisguanidine complexes with nitric oxide and the formation of intermediate species were monitored via UV-vis spectroscopy at low temperature, with the occurrence of characteristic absorption bands. The origin of the emerging species and their character were substantiated by electron paramagnetic resonance (EPR) measurements and density functional theory (DFT) studies showing a delocalized {CuNO}11 radical species. Furthermore, this system was transferred to the SuperFocus mixer setup, which allows rapid mixing and the determination of decay constants at ambient temperatures of the thermally sensitive species. However, these experiments demonstrated the limits of these systems, such as the NO saturation in organic solvents and a preferably precise temperature control within the SuperFocus mixer, which should be addressed in the future.


Bloch oscillations sustained by nonlinearity

R. Driben, V.V. Konotop, T. Meier, A.V. Yulin, Scientific Reports (2017)

DOI


A microscopic approach to ultrafast near band gap photocurrents in bulk semiconductors

R. Podzimski, H.T. Duc, T. Meier, in: Ultrafast Phenomena and Nanophotonics XXI, 2017

DOI


Directional optical switching and transistor functionality using optical parametric oscillation in a spinor polariton fluid

P. Lewandowski, S.M.H. Luk, C.K.P. Chan, P.T. Leung, N.H. Kwong, R. Binder, S. Schumacher, Optics Express (2017), 25(25)

DOI


Ultrafast Electronic Energy Transfer in an Orthogonal Molecular Dyad

C. Wiebeler, F. Plasser, G.J. Hedley, A. Ruseckas, I.D.W. Samuel, S. Schumacher, The Journal of Physical Chemistry Letters (2017), pp. 1086-1092

DOI


On-Surface Site-Selective Cyclization of Corrole Radicals

S. Tebi, M. Paszkiewicz, H. Aldahhak, F. Allegretti, S. Gonglach, M. Haas, M. Waser, P.S. Deimel, P.C. Aguilar, Y. Zhang, A.C. Papageorgiou, D.A. Duncan, J.V. Barth, W.G. Schmidt, R. Koch, U. Gerstmann, E. Rauls, F. Klappenberger, W. Schöfberger, S. Müllegger, ACS Nano (2017), pp. 3383-3391

DOI


Efficient PAW-based bond strength analysis for understanding the In/Si(111)(8 × 2) – (4 × 1) phase transition

A. Lücke, U. Gerstmann, T.D. Kühne, W.G. Schmidt, Journal of Computational Chemistry (2017), 38(26), pp. 2276-2282

A numerically efficient yet highly accurate implementation of the crystal orbital Hamilton population (COHP) scheme for plane-wave calculations is presented. It is based on the projector-augmented wave (PAW) formalism in combination with norm-conserving pseudopotentials and allows to extract chemical interactions between atoms from band-structure calculations even for large and complex systems. The potential of the present COHP implementation is demonstrated by an in-depth analysis of the intensively investigated metal-insulator transition in atomic-scale indium wires self-assembled on the Si(111) surface. Thereby bond formation between In atoms of adjacent zigzag chains is found to be instrumental for the phase change. © 2017 Wiley Periodicals, Inc.


X-Ray Magnetic and Natural Circular Dichroism from First Principles: Calculation of K- and L1-Edge Spectra

N. Bouldi, N.J. Vollmers, C.G. Delpy-Laplanche, Y. Joly, A. Juhin, P. Sainctavit, C. Brouder, M. Calandra, L. Paulatto, F. Mauri, U. Gerstmann, Physical Review B (2017), 96(8), pp. 085123

DOI


ms2: A Molecular Simulation Tool for Thermodynamic Properties, Release 3.0

G. Rutkai, A. Köster, G. Guevara-Carrion, T. Janzen, M. Schappals, C.W. Glass, M. Bernreuther, A. Wafai, S. Stephan, M. Kohns, S. Reiser, S. Deublein, M. Horsch, H. Hasse, J. Vrabec, Computer Physics Communications (2017), 221, pp. 343-351

DOI


Enhanced columnar mesophase range through distortions in arene cores

J. Vollbrecht, C. Wiebeler, S. Schumacher, H. Bock, H. Kitzerow, Molecular Crystals and Liquid Crystals (2017), pp. 66-73

DOI


Consistent Atomic Geometries and Electronic Structure of Five Phases of Potassium Niobate from Density-Functional Theory

F. Schmidt, M. Landmann, E. Rauls, N. Argiolas, S. Sanna, W.G. Schmidt, A. Schindlmayr, Advances in Materials Science and Engineering (2017), pp. 1-13

<jats:p>We perform a comprehensive theoretical study of the structural and electronic properties of potassium niobate (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">K</mml:mi><mml:mi mathvariant="normal">N</mml:mi><mml:mi mathvariant="normal">b</mml:mi><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn mathvariant="normal">3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>) in the cubic, tetragonal, orthorhombic, monoclinic, and rhombohedral phase, based on density-functional theory. The influence of different parametrizations of the exchange-correlation functional on the investigated properties is analyzed in detail, and the results are compared to available experimental data. We argue that the PBEsol and AM05 generalized gradient approximations as well as the RTPSS meta-generalized gradient approximation yield consistently accurate structural data for both the external and internal degrees of freedom and are overall superior to the local-density approximation or other conventional generalized gradient approximations for the structural characterization of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">K</mml:mi><mml:mi mathvariant="normal">N</mml:mi><mml:mi mathvariant="normal">b</mml:mi><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn mathvariant="normal">3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>. Band-structure calculations using a HSE-type hybrid functional further indicate significant near degeneracies of band-edge states in all phases which are expected to be relevant for the optical response of the material.</jats:p>


Polaron optical absorption in congruent lithium niobate from time-dependent density-functional theory

M. Friedrich, W.G. Schmidt, A. Schindlmayr, S. Sanna, Physical Review Materials (2017), 1(5)

DOI


Advanced capabilities for materials modelling with Quantum ESPRESSO

P. Giannozzi, O. Andreussi, T. Brumme, O. Bunau, M. Buongiorno Nardelli, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, M. Cococcioni, N. Colonna, I. Carnimeo, A. Dal Corso, S. de Gironcoli, P. Delugas, R.A. DiStasio, A. Ferretti, A. Floris, G. Fratesi, G. Fugallo, R. Gebauer, U. Gerstmann, F. Giustino, T. Gorni, J. Jia, M. Kawamura, H. Ko, A. Kokalj, E. Küçükbenli, M. Lazzeri, M. Marsili, N. Marzari, F. Mauri, N.L. Nguyen, H. Nguyen, A. Otero-de-la-Roza, L. Paulatto, S. Poncé, D. Rocca, R. Sabatini, B. Santra, M. Schlipf, A.P. Seitsonen, A. Smogunov, I. Timrov, T. Thonhauser, P. Umari, N. Vast, X. Wu, S. Baroni, Journal of Physics: Condensed Matter (2017), 29(46)

DOI


2016

Assessing the accuracy of improved force-matched water models derived from Ab initio molecular dynamics simulations

A. Köster, T. Spura, G. Rutkai, J. Kessler, H. Wiebeler, J. Vrabec, T.D. Kühne, Journal of Computational Chemistry (2016), 37(19), pp. 1828-1838

The accuracy of water models derived from ab initio molecular dynamics simulations by means on an improved force-matching scheme is assessed for various thermodynamic, transport, and structural properties. It is found that although the resulting force-matched water models are typically less accurate than fully empirical force fields in predicting thermodynamic properties, they are nevertheless much more accurate than generally appreciated in reproducing the structure of liquid water and in fact superseding most of the commonly used empirical water models. This development demonstrates the feasibility to routinely parametrize computationally efficient yet predictive potential energy functions based on accurate ab initio molecular dynamics simulations for a large variety of different systems. © 2016 Wiley Periodicals, Inc.


Temperature-Dependent Hole Mobility and Its Limit in Crystal-Phase P3HT Calculated from First Principles

A. Lücke, F. Ortmann, M. Panhans, S. Sanna, E. Rauls, U. Gerstmann, W.G. Schmidt, The Journal of Physical Chemistry B (2016), 120, pp. 5572-5580

DOI


Monte-Carlo Simulation Balancing Revisited

T. Graf, M. Platzner, in: IEEE Computational Intelligence and Games, 2016


Vibrational properties ofLiNb1−xTaxO3mixed crystals

M. Rüsing, S. Sanna, S. Neufeld, G. Berth, W.G. Schmidt, A. Zrenner, H. Yu, Y. Wang, H. Zhang, Physical Review B (2016)

DOI


Grand canonical Peierls transition in In/Si(111)

E. Jeckelmann, S. Sanna, W.G. Schmidt, E. Speiser, N. Esser, Physical Review B (2016), 93(24)

DOI


Impurity-Mediated Early Condensation of a Charge Density Wave in an Atomic Wire Array

H.W. Yeom, D.M. Oh, S. Wippermann, W.G. Schmidt, ACS Nano (2016), 10, pp. 810-814

DOI


Indium oxide inverse opal films synthesized by structure replication method

S. Amrehn, D. Berghoff, A. Nikitin, M. Reichelt, X. Wu, T. Meier, T. Wagner, Photonics and Nanostructures - Fundamentals and Applications (2016), 19, pp. 55-63

DOI


Light scattering by ice crystals of cirrus clouds: From exact numerical methods to physical-optics approximation

A. Konoshonkin, A. Borovoi, N. Kustova, H. Okamoto, H. Ishimoto, Y. Grynko, J. Förstner, Journal of Quantitative Spectroscopy and Radiative Transfer (2016), 195, pp. 132-140

The problem of light scattering by ice crystals of cirrus clouds is considered in the case of a hexagonal ice plate with different distributions over crystal orientations. The physical-optics approximation based on (E, M)-diffraction theory is compared with two exact numerical methods: the finite difference time domain (FDTD) and the discontinuous Galerkin time domain (DGTD) in order to estimate its accuracy and limits of applicability. It is shown that the accuracy of the physical-optics approximation is estimated as 95% for the averaged backscattering Mueller matrix for particles with size parameter more than 120. Furthermore, the simple expression that allows one to estimate the minimal number of particle orientations required for appropriate spatial averaging has been derived.


Strain-induced quasi-one-dimensional rare-earth silicide structures on Si(111)

F. Timmer, R. Oelke, C. Dues, S. Sanna, W.G. Schmidt, M. Franz, S. Appelfeller, M. Dähne, J. Wollschläger, Physical Review B (2016), 94(20)

DOI


Density functional theory of the CuA-like Cu2S2 diamond core in Cu 2II(NGuaS)2Cl2

M. Witte, U. Gerstmann, A. Neuba, G. Henkel, W.G. Schmidt, Journal of Computational Chemistry (2016), 37, pp. 1005-1018

DOI


Photocurrents in semiconductors and semiconductor quantum wells analyzed by k.p-based Bloch equations

R. Podzimski, H.T. Duc, S. Priyadarshi, C. Schmidt, M. Bieler, T. Meier, in: Ultrafast Phenomena and Nanophotonics XX, 2016

DOI


Ultrafast dynamical response of the lower exciton-polariton branch in CdZnTe

J. Lohrenz, S. Melzer, C. Ruppert, I.A. Akimov, H. Mariette, M. Reichelt, A. Trautmann, T. Meier, M. Betz, Physical Review B (2016), 93(7)

DOI


Determination of the material properties of polymers using laser-generated broadband ultrasound

L. Claes, T. Meyer, F. Bause, J. Rautenberg, B. Henning, Journal of Sensors and Sensor Systems (2016), 5(1), pp. 187-196


Using Approximate Computing in Scientific Codes

M. Lass, T. Kühne, C. Plessl, in: Workshop on Approximate Computing (AC), 2016


Experimental and Theoretical High-Energy-Resolution X-ray Absorption Spectroscopy: Implications for the Investigation of the Entatic State

N.J. Vollmers, P. Müller, A. Hoffmann, S. Herres-Pawlis, M. Rohrmüller, W.G. Schmidt, U. Gerstmann, M. Bauer, Inorganic Chemistry (2016), 55, pp. 11694-11706

DOI


Atomic size effects studied by transport in single silicide nanowires

I. Miccoli, F. Edler, H. Pfnür, S. Appelfeller, M. Dähne, K. Holtgrewe, S. Sanna, W.G. Schmidt, C. Tegenkamp, Physical Review B (2016)

DOI


Light scattering by irregular particles much larger than the wavelength with wavelength-scale surface roughness

Y. Grynko, Y. Shkuratov, J. Förstner, Optics Letters (2016), 41(15)

We simulate light scattering by random irregular particles that have dimensions much larger than the wavelength of incident light at the size parameter of 𝑋=200 using the discontinuous Galerkin time domain method. A comparison of the DGTD solution for smoothly faceted particles with that obtained with a geometric optics model shows good agreement for the scattering angle curves of intensity and polarization. If a wavelength-scale surface roughness is introduced, diffuse scattering at rough interface results in smooth and featureless curves for all scattering matrix elements which is consistent with the laboratory measurements of real samples.


The role of electromagnetic interactions in second harmonic generation from plasmonic metamaterials

J. Alberti, H. Linnenbank, S. Linden, Y. Grynko, J. Förstner, Applied Physics B (2016), 122(2), pp. 45-50

We report on second harmonic generation spectroscopy on a series of rectangular arrays of split-ring resonators. Within the sample series, the lattice constants are varied, but the area of the unit cell is kept fixed. The SHG signal intensity of the different arrays upon resonant excitation of the fundamental plasmonic mode strongly depends on the respective arrangement of the split-ring resonators. This finding can be explained by variations of the electromagnetic interactions between the split-ring resonators in the different arrays. The experimental results are in agreement with numerical calculations based on the discontinuous Galerkin time-domain method. (PDF) The role of electromagnetic interactions.... Available from: https://www.researchgate.net/publication/297612326_The_role_of_electromagnetic_interactions_in_second_harmonic_generation_from_plasmonic_metamaterials [accessed Aug 13 2018].


Ultrasonic transmission measurements in the characterization of viscoelasticity utilizing polymeric waveguides

F. Bause, J. Rautenberg, N. Feldmann, M. Webersen, L. Claes, H. Gravenkamp, B. Henning, Measurement Science and Technology (2016), 27(10)

DOI


Optical response of the Cu2S2diamond core in Cu2II(NGuaS)2Cl2

M. Witte, B. Grimm-Lebsanft, A. Goos, S. Binder, M. Rübhausen, M. Bernard, A. Neuba, S. Gorelsky, U. Gerstmann, G. Henkel, W.G. Schmidt, S. Herres-Pawlis, Journal of Computational Chemistry (2016), 37(23-24), pp. 2181-2192

DOI


Vibration eigenmodes of the Au-(5×2)/Si(111) surface studied by Raman spectroscopy and first-principles calculations

M. Liebhaber, B. Halbig, U. Bass, J. Geurts, S. Neufeld, S. Sanna, W.G. Schmidt, E. Speiser, J. Räthel, S. Chandola, N. Esser, Physical Review B (2016), 94(23)

DOI


LiNbO3electronic structure: Many-body interactions, spin-orbit coupling, and thermal effects

A. Riefer, M. Friedrich, S. Sanna, U. Gerstmann, A. Schindlmayr, W.G. Schmidt, Physical Review B (2016)

DOI


Light scattering by ice crystals of cirrus clouds: comparison of the physical optics methods

A.V. Konoshonkin, N.V. Kustova, A.G. Borovoi, Y. Grynko, J. Förstner, Journal of Quantitative Spectroscopy and Radiative Transfer (2016), 182, pp. 12-23

The physical optics approximations are derived from the Maxwell equations. The scattered field equations by Kirchhoff, Stratton-Chu, Kottler and Franz are compared and discussed. It is shown that in the case of faceted particles, these equations reduce to a sum of the diffraction integrals, where every diffraction integral is associated with one plane–parallel optical beam leaving a particle facet. In the far zone, these diffraction integrals correspond to the Fraunhofer diffraction patterns. The paper discusses the E-, M- and (E, M)-diffraction theories as applied to ice crystals of cirrus clouds. The comparison to the exact solution obtained by the discontinuous Galerkin time domain method shows that the Kirchhoff diffraction theory is preferable.


Characterization of Continuous-fiber Reinforced Thermoplastics Using Thermoacoustically Excited Ultrasonic Lamb Waves

M. Webersen, S. Johannesmann, L. Claes, B. Henning, in: 2016 IEEE IUS~Proceedings, 2016


Improved parameterization of the quantum harmonic oscillator model based on localized wannier functions to describe Van der Waals interactions in density functional theory

P. Partovi-Azar, M. Berg, S. Sanna, T.D. Kühne, International Journal of Quantum Chemistry (2016), 116(15), pp. 1160-1165

Recently, the quantum harmonic oscillator model has been combined with maximally localized Wannier functions to account for long-range dispersion interactions in density functional theory calculations (Silvestrelli, J. Chem. Phys. 2013, 139, 054106). Here, we present a new, improved set of values for the three parameters involved in this scheme. To test the new parameter set we have computed the potential energy curves for various systems, including an isolated Ar2 dimer, two N2 dimers interacting within different configurations, and a water molecule physisorbed on pristine graphene. While the original set of parameters generally overestimates the interaction energies and underestimates the equilibrium distances, the new parameterization substantially improves the agreement with experimental and theoretical reference values. © 2016 Wiley Periodicals, Inc.


Solving the Pre-Marshalling Problem to Optimality with A* and IDA*

K. Tierney, D. Pacino, S. Voß, Flexible Services and Manufacturing Journal (2016), pp. 223-259

DOI


Surface vibrational Raman modes of In:Si(111)(4×1)and(8×2)nanowires

E. Speiser, N. Esser, S. Wippermann, W.G. Schmidt, Physical Review B (2016), 94(7)

DOI


Inhomogeneous and Homogeneous Line Broadening of Optical Spectra of PTCDA Molecules Adsorbed at Step Edges of Alkali Halide Surfaces

A. Paulheim, C. Marquardt, H. Aldahhak, E. Rauls, W.G. Schmidt, M. Sokolowski, The Journal of Physical Chemistry C (2016), 10, pp. 11926-11937

DOI


Using Deep Convolutional Neural Networks in Monte Carlo Tree Search

T. Graf, M. Platzner, in: Computer and Games, 2016


Rare-earth silicide thin films on the Si(111) surface

S. Sanna, C. Dues, W.G. Schmidt, F. Timmer, J. Wollschläger, M. Franz, S. Appelfeller, M. Dähne, Physical Review B (2016), 93(19)

DOI


LiTaO3 phonon dispersion and ferroelectric transition calculated from first principles

M. Friedrich, A. Schindlmayr, W.G. Schmidt, S. Sanna, physica status solidi (b) (2016), 253(4), pp. 683-689

DOI


Surface induced vibrational modes in the fluorescence spectra of PTCDA adsorbed on the KCl(100) and NaCl(100) surfaces

A. Paulheim, C. Marquardt, M. Sokolowski, M. Hochheim, T. Bredow, H. Aldahhak, E. Rauls, W.G. Schmidt, Physical Chemistry Chemical Physics (2016), 18, pp. 32891-32902

<p>We report a combined experiment-theory study on low energy vibrational modes in fluorescence spectra of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) molecules.</p>


Manipulation resolves non-trivial structure of corrole monolayer on Ag(111)

S. Tebi, H. Aldahhak, G. Serrano, W. Schöfberger, E. Rauls, W.G. Schmidt, R. Koch, S. Müllegger, Nanotechnology (2016), 27

DOI


2015

Modeling atomic force microscopy at LiNbO 3 surfaces from first-principles

S. Sanna, C. Dues, W.G. Schmidt, Computational Materials Science (2015), pp. 145-150

DOI


Mechanism for nuclear and electron spin excitation by radio frequency current

S. Müllegger, E. Rauls, U. Gerstmann, S. Tebi, G. Serrano, S. Wiespointner-Baumgarthuber, W.G. Schmidt, R. Koch, Physical Review B (2015), 92(22)

DOI


The Cu2O2torture track for a real-life system: [Cu2(btmgp)2O2]2+oxo and peroxo species in density functional calculations†

M. Rohrmüller, A. Hoffmann, C. Thierfelder, S. Herres-Pawlis, W.G. Schmidt, Journal of Computational Chemistry (2015), 36(21-22), pp. 1672-1685

DOI


LiTaO3 phonon dispersion and ferroelectric transition calculated from first principles

M. Friedrich, A. Schindlmayr, W.G. Schmidt, S. Sanna, physica status solidi (b) (2015), 253(4), pp. 683-689

DOI


GaNm-plane: Atomic structure, surface bands, and optical response

M. Landmann, E. Rauls, W.G. Schmidt, M. Neumann, E. Speiser, N. Esser, Physical Review B (2015)

DOI


Adaptive Playouts in Monte-Carlo Tree Search with Policy-Gradient Reinforcement Learning

T. Graf, M. Platzner, in: Advances in Computer Games: 14th International Conference, ACG 2015, Leiden, The Netherlands, July 1-3, 2015, Revised Selected Papers, Springer International Publishing, 2015, pp. 1-11

DOI


Single PTCDA molecules on planar and stepped KCl and NaCl(100) surfaces

H. Aldahhak, W.G. Schmidt, E. Rauls, Surface Science (2015), pp. 278-281

DOI


GaNm-plane: Atomic structure, surface bands, and optical response

M. Landmann, E. Rauls, W.G. Schmidt, M. Neumann, E. Speiser, N. Esser, Physical Review B (2015), 91

DOI


Phonon dispersion and zero-point renormalization of LiNbO3from density-functional perturbation theory

M. Friedrich, A. Riefer, S. Sanna, W.G. Schmidt, A. Schindlmayr, Journal of Physics: Condensed Matter (2015), 27

DOI


Barrier-free subsurface incorporation of 3d metal atoms into Bi(111) films

C. Klein, N.J. Vollmers, U. Gerstmann, P. Zahl, D. Lükermann, G. Jnawali, H. Pfnür, C. Tegenkamp, P. Sutter, W.G. Schmidt, M. Horn-von Hoegen, Physical Review B (2015), 91(19)

DOI


Diindenoperylene adsorption on Cu(111) studied with density-functional theory

H. Aldahhak, E. Rauls, W.G. Schmidt, Surface Science (2015), pp. 260-265

DOI


A panel of peralkylated sulfur–guanidine type bases: Novel pro-ligands for use in biomimetic coordination chemistry

A. Neuba, M. Rohrmüller, R. Hölscher, W.G. Schmidt, G. Henkel, Inorganica Chimica Acta (2015), 430, pp. 225-238

DOI


Defect complexes in congruentLiNbO3and their optical signatures

Y. Li, W.G. Schmidt, S. Sanna, Physical Review B (2015)

DOI


Modeling atomic force microscopy at LiNbO 3 surfaces from first-principles

S. Sanna, C. Dues, W.G. Schmidt, Computational Materials Science (2015), 103, pp. 145-150

DOI


Liquid Crystal (8CB) Molecular Adsorption on Lithium Niobate Z-Cut Surfaces

C. Braun, S. Sanna, W.G. Schmidt, The Journal of Physical Chemistry C (2015), pp. 9342-9346

DOI


Interwire coupling forIn(4×1)/Si(111) probed by surface transport

F. Edler, I. Miccoli, S. Demuth, H. Pfnür, S. Wippermann, A. Lücke, W.G. Schmidt, C. Tegenkamp, Physical Review B (2015), 92(8)

DOI


Localization Length Index and Subleading Corrections in a Chalker-Coddington Model: A Numerical Study

W. Nuding, A. Klümper, A. Sedrakyan, Physical Review B (2015), 91, pp. 115107

DOI


Water adsorbate influence on the Cu(110) surface optical response

A. Baghbanpourasl, W.G. Schmidt, M. Denk, C. Cobet, M. Hohage, P. Zeppenfeld, K. Hingerl, Surface Science (2015), 641, pp. 231-236

DOI


Influence of Structural Defects and Oxidation onto Hole Conductivity in P3HT

A. Lücke, W.G. Schmidt, E. Rauls, F. Ortmann, U. Gerstmann, The Journal of Physical Chemistry B (2015), 119, pp. 6481-6491

DOI


Raman scattering efficiency inLiTaO3andLiNbO3crystals

S. Sanna, S. Neufeld, M. Rüsing, G. Berth, A. Zrenner, W.G. Schmidt, Physical Review B (2015)

DOI


Creation of vortices by torque in multidimensional media with inhomogeneous defocusing nonlinearity

R. Driben, T. Meier, B.A. Malomed, Scientific Reports (2015), 5, pp. 9420

DOI


2014

Rashba splitting and relativistic energy shifts in In/Si(111) nanowires

U. Gerstmann, N.J. Vollmers, A. Lücke, M. Babilon, W.G. Schmidt, Physical Review B (2014), 89(16)

DOI


Modeling intrinsic defects in LiNbO3 within the Slater-Janak transition state model

Y. Li, S. Sanna, W.G. Schmidt, The Journal of Chemical Physics (2014)

DOI


Common Fate Graph Patterns in Monte Carlo Tree Search for Computer Go

T. Graf, M. Platzner, in: 2014 IEEE Conference on Computational Intelligence and Games, 2014, pp. 1-8

DOI


Geometrical and optical benchmarking of copper(II) guanidine-quinoline complexes: Insights from TD-DFT and many-body perturbation theory (part II)

A. Hoffmann, M. Rohrmüller, A. Jesser, I. dos Santos Vieira, W.G. Schmidt, S. Herres-Pawlis, Journal of Computational Chemistry (2014), 35(29-30), pp. 2146-2161

DOI


Adsorption of PTCDA on Terraces and at Steps Sites of the KCl(100) Surface

Q. Guo, A. Paulheim, M. Sokolowski, H. Aldahhak, E. Rauls, W.G. Schmidt, The Journal of Physical Chemistry C (2014), 118, pp. 29911-29918

DOI


Temperature dependent LiNbO3(0001): Surface reconstruction and surface charge

S. Sanna, R. Hölscher, W.G. Schmidt, Applied Surface Science (2014), pp. 70-78

DOI


Oxygen adsorbates on the Si(111)4×1-In metallic atomic wire: Scanning tunneling microscopy and density-functional theory calculations

D.M. Oh, S. Wippermann, W.G. Schmidt, H.W. Yeom, Physical Review B (2014), 90(15)

DOI


The atomic structure of ternary amorphous TixSi1−xO2hybrid oxides

M. Landmann, T. Köhler, E. Rauls, T. Frauenheim, W.G. Schmidt, Journal of Physics: Condensed Matter (2014), 26

DOI


Unraveling theLiNbO3X-cut surface by atomic force microscopy and density functional theory

S. Sanna, W.G. Schmidt, S. Rode, S. Klassen, A. Kühnle, Physical Review B (2014), 89(7)

DOI


Modeling LiNbO3 Surfaces at Ambient Conditions

R. Hölscher, W.G. Schmidt, S. Sanna, The Journal of Physical Chemistry C (2014), pp. 10213-10220

DOI


2013

Vibrational Fingerprints of LiNbO3-LiTaO3Mixed Crystals

S. Sanna, A. Riefer, S. Neufeld, W.G. Schmidt, G. Berth, M. Rüsing, A. Widhalm, A. Zrenner, Ferroelectrics (2013), 447, pp. 63-68

DOI


Optical response of stoichiometric and congruent lithium niobate from first-principles calculations

A. Riefer, S. Sanna, A. Schindlmayr, W.G. Schmidt, Physical Review B (2013), 87(19)

DOI


Charge compensation by long-period reconstruction in strongly polar lithium niobate surfaces

S. Sanna, S. Rode, R. Hölscher, S. Klassen, C. Marutschke, K. Kobayashi, H. Yamada, W.G. Schmidt, A. Kühnle, Physical Review B (2013), 88

DOI


LiNb1-xTaxO3Electronic Structure and Optical Response fromFirst-PrinciplesCalculations

A. Riefer, S. Sanna, W.G. Schmidt, Ferroelectrics (2013), 447, pp. 78-85

DOI


Bis-μ-oxo and μ-η2:η2-peroxo dicopper complexes studied within (time-dependent) density-functional and many-body perturbation theory

M. Rohrmüller, S. Herres-Pawlis, M. Witte, W.G. Schmidt, Journal of Computational Chemistry (2013), 34, pp. 1035-1045

DOI


Adsorption of PTCDA on NaCl(100) and KCl(100)

H. Aldahhak, W.G. Schmidt, E. Rauls, Surface Science (2013), 617, pp. 242-248

DOI


Atomic Structure of Interface States in Silicon Heterojunction Solar Cells

B.M. George, J. Behrends, A. Schnegg, T.F. Schulze, M. Fehr, L. Korte, B. Rech, K. Lips, M. Rohrmüller, E. Rauls, W.G. Schmidt, U. Gerstmann, Physical Review Letters (2013), 110(13)

DOI


LiNb1-xTaxO3Electronic Structure and Optical Response fromFirst-PrinciplesCalculations

A. Riefer, S. Sanna, W.G. Schmidt, Ferroelectrics (2013), 447, pp. 78-85

DOI


Geometrical and optical benchmarking of copper guanidine-quinoline complexes: Insights from TD-DFT and many-body perturbation theory†

A. Jesser, M. Rohrmüller, W.G. Schmidt, S. Herres-Pawlis, Journal of Computational Chemistry (2013), 35(1-2), pp. 1-17

DOI


2012

Polarization-dependent methanol adsorption on lithium niobate Z-cut surfaces

A. Riefer, S. Sanna, W.G. Schmidt, Physical Review B (2012), 86(12)

DOI


The electronic structure and optical response of rutile, anatase and brookite TiO2

M. Landmann, E. Rauls, W.G. Schmidt, Journal of Physics: Condensed Matter (2012), 24

DOI


Atomic-resolution imaging of the polar (0001¯) surface of LiNbO3in aqueous solution by frequency modulation atomic force microscopy

S. Rode, R. Hölscher, S. Sanna, S. Klassen, K. Kobayashi, H. Yamada, W.G. Schmidt, A. Kühnle, Physical Review B (2012), 86(7)

DOI


Atomistic Picture of Charge Density Wave Formation at Surfaces

S. Wall, B. Krenzer, S. Wippermann, S. Sanna, F. Klasing, A. Hanisch-Blicharski, M. Kammler, W.G. Schmidt, M. Horn-von Hoegen, Physical Review Letters (2012), 109(18)

DOI


Fingerprints of order and disorder in the electronic and optical properties of crystalline and amorphous TiO2

M. Landmann, T. Köhler, S. Köppen, E. Rauls, T. Frauenheim, W.G. Schmidt, Physical Review B (2012), 86(6)

DOI


2-Aminopyrimidine-silver(I) based organic semiconductors: Electronic structure and optical response

A. Riefer, E. Rauls, W.G. Schmidt, J. Eberhard, I. Stoll, J. Mattay, Physical Review B (2012), 85(16)

DOI


Adsorption of OH and H at the LiNbO3(0001) surface

R. Hölscher, S. Sanna, W.G. Schmidt, physica status solidi (c) (2012), 9(6), pp. 1361-1365

DOI


In-Si(111)(4 × 1)/(8 × 2) nanowires: Electron transport, entropy, and metal-insulator transition

W.G. Schmidt, S. Wippermann, S. Sanna, M. Babilon, N.J. Vollmers, U. Gerstmann, physica status solidi (b) (2012), 249(2), pp. 343-359

DOI


Ferroelectric phase transition in LiNbO3: Insights from molecular dynamics

S. Sanna, W.G. Schmidt, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control (2012), 59(9), pp. 1925-1928

DOI


Linear and nonlinear optical response of LiNbO3 calculated from first principles

A. Riefer, S. Sanna, A.V. Gavrilenko, W.G. Schmidt, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control (2012), 59(9), pp. 1929-1933

DOI


Substrate Induced Thermal Decomposition of Perfluoro-Pentacene Thin Films on the Coinage Metals

C. Schmidt, T. Breuer, S. Wippermann, W.G. Schmidt, G. Witte, The Journal of Physical Chemistry C (2012), 116, pp. 24098-24106

DOI


Interplay between metal-free phthalocyanine molecules and Au(110) substrates

E. Rauls, W.G. Schmidt, T. Pertram, K. Wandelt, Surface Science (2012), 606, pp. 1120-1125

DOI


pH-dependent structure and energetics of H2O/MgO(100)

P. Thissen, V. Thissen, S. Wippermann, Y.J. Chabal, G. Grundmeier, W.G. Schmidt, Surface Science (2012), 606, pp. 902-907

DOI


2011

Influence of Na adsorption on the quantum conductance and metal-insulator transition of the In-Si(111)(4×1)–(8×2) nanowire array

W.G. Schmidt, M. Babilon, C. Thierfelder, S. Sanna, S. Wippermann, Physical Review B (2011), 84(11)

DOI


Asymmetric saddling of single porphyrin molecules on Au(111)

S. Müllegger, M. Rashidi, T. Lengauer, E. Rauls, W.G. Schmidt, G. Knör, W. Schöfberger, R. Koch, Physical Review B (2011), 83(16)

DOI


Band offsets in cubic GaN/AlN superlattices

C. Mietze, M. Landmann, E. Rauls, H. Machhadani, S. Sakr, M. Tchernycheva, F.H. Julien, W.G. Schmidt, K. Lischka, D.J. As, Physical Review B (2011), 83(19)

DOI


Vibrational properties of the LiNbO3 z-surfaces

S. Sanna, G. Berth, W. Hahn, A. Widhalm, A. Zrenner, W.G. Schmidt, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control (2011), 58(9), pp. 1751-1756

DOI


Methane adsorption on graphene from first principles including dispersion interaction

C. Thierfelder, M. Witte, S. Blankenburg, E. Rauls, W.G. Schmidt, Surface Science (2011), 605, pp. 746-749

DOI


Group-VII point defects in ZnSe

L.S. dos Santos, W.G. Schmidt, E. Rauls, Physical Review B (2011), 84(11)

DOI


Preserving Charge and Oxidation State of Au(III) Ions in an Agent-Functionalized Nanocrystal Model System

S. Müllegger, W. Schöfberger, M. Rashidi, T. Lengauer, F. Klappenberger, K. Diller, K. Kara, J.V. Barth, E. Rauls, W.G. Schmidt, R. Koch, ACS Nano (2011), 5(8), pp. 6480-6486

DOI


Barium titanate ground- and excited-state properties from first-principles calculations

S. Sanna, C. Thierfelder, S. Wippermann, T.P. Sinha, W.G. Schmidt, Physical Review B (2011), 83(5)

DOI


Localised Phonon Modes at LiNbO3(0001) Surfaces

S. Sanna, G. Berth, W. Hahn, A. Widhalm, A. Zrenner, W.G. Schmidt, Ferroelectrics (2011), 419, pp. 1-8

DOI


2010

Tuning quantum-dot based photonic devices with liquid crystals

K.A. Piegdon, S. Declair, J. Förstner, T. Meier, H. Matthias, M. Urbanski, H. Kitzerow, D. Reuter, A.D. Wieck, A. Lorke, C. Meier, Optics Express (2010), 18(8)

Microdisks made from GaAs with embedded InAs quantum dots are immersed in the liquid crystal 4-cyano-4’-pentylbiphenyl (5CB). The quantum dots serve as emitters feeding the optical modes of the photonic cavity. By changing temperature, the liquid crystal undergoes a phase transition from the isotropic to the nematic state, which can be used as an effective tuning mechanism of the photonic modes of the cavity. In the nematic state, the uniaxial electrical anisotropy of the liquid crystal molecules can be exploited for orienting the material in an electric field, thus externally controlling the birefringence of the material. Using this effect, an electric field induced tuning of the modes is achieved. Numerical simulations using the finite-differences time-domain (FDTD) technique employing an anisotropic dielectric medium allow to understand the alignment of the liquid crystal molecules on the surface of the microdisk resonator.


Ab initio investigation of the LiNbO3(0001) surface

S. Sanna, A.V. Gavrilenko, W.G. Schmidt, physica status solidi (c) (2010), 7(2), pp. 145-148

DOI


Understanding the cubic AlN growth plane from first principles

E. Rauls, J. Wiebe, W.G. Schmidt, Journal of Crystal Growth (2010), 312, pp. 2892-2895

DOI


Dissociative and molecular adsorption of water onα-Al2O3(0001)

S. Wippermann, W.G. Schmidt, P. Thissen, G. Grundmeier, physica status solidi (c) (2010), 7(2), pp. 137-140

DOI


First-principles investigation of CO adsorption on Pt/Ge(001)-(4×2)

A. Krivosheeva, S. Sanna, W.G. Schmidt, Computational Materials Science (2010), 49(4), pp. 895-898

DOI


Chemical reactivity on surfaces: Modeling the imide synthesis from DATP and PTCDA on Au(111)

E. Rauls, S. Blankenburg, W.G. Schmidt, Physical Review B (2010), 81(12)

DOI


First-principles study of water adsorption and a high-density interfacial ice structure on(1×1)-O/Rh(111)

C. Thierfelder, W.G. Schmidt, Physical Review B (2010), 82(11)

DOI


Do we know the band gap of lithium niobate?

C. Thierfelder, S. Sanna, A. Schindlmayr, W.G. Schmidt, physica status solidi (c) (2010), 7(2), pp. 362-365

DOI


Catalytic Action of a Cu(111) Surface on Tetraazaperopyrene Polymerization

S. Blankenburg, E. Rauls, W.G. Schmidt, The Journal of Physical Chemistry Letters (2010), 1, pp. 3266-3270

DOI


GaN growth on LiNbO3 (0001) - a first-principles simulation

S. Sanna, W.G. Schmidt, physica status solidi (c) (2010), 7(7-8), pp. 2272-2274

DOI


Lithium niobateX-cut,Y-cut, andZ-cut surfaces fromab initiotheory

S. Sanna, W.G. Schmidt, Physical Review B (2010), 81(21)

DOI


Reversal of Coherently Controlled Ultrafast Photocurrents by Band Mixing in Undoped GaAs Quantum Wells

S. Priyadarshi, A.M. Racu, K. Pierz, U. Siegner, M. Bieler, H.T. Duc, J. Förstner, T. Meier, Physical Review Letters (2010), 104(21)

It is demonstrated that valence-band mixing in GaAs quantum wells tremendously modifies electronic transport. A coherent control scheme in which ultrafast currents are optically injected into undoped GaAs quantum wells upon excitation with femtosecond laser pulses is employed. An oscillatory dependence of the injection current amplitude and direction on the excitation photon energy is observed. A microscopic theoretical analysis shows that this current reversal is caused by the coupling of the light- and heavy-hole bands and that the hole currents dominate the overall current response. These surprising consequences of band mixing illuminate fundamental physics as they are unique for experiments which are able to monitor electronic transport resulting from carriers with relatively large momenta.


Ab initiog-tensor calculation for paramagnetic surface states: hydrogen adsorption at Si surfaces

U. Gerstmann, M. Rohrmüller, F. Mauri, W.G. Schmidt, physica status solidi (c) (2010), 7(2), pp. 157-160

DOI


Optical anisotropy of Si(111)-(4 × 1)/(8 × 2)-In nanowires calculated fromfirst-principles

S. Wippermann, W.G. Schmidt, F. Bechstedt, S. Chandola, K. Hinrichs, M. Gensch, N. Esser, K. Fleischer, J.F. McGilp, physica status solidi (c) (2010), 7(2), pp. 133-136

DOI


Temperature dependent stability of self-assembled molecular rows

S. Blankenburg, W.G. Schmidt, physica status solidi (c) (2010), 7(2), pp. 415-417

DOI


Entropy Explains Metal-Insulator Transition of the Si(111)-In Nanowire Array

S. Wippermann, W.G. Schmidt, Physical Review Letters (2010), 105(12)

DOI


The physics of highly ordered molecular rows

S. Blankenburg, E. Rauls, W.G. Schmidt, physica status solidi (c) (2010), 7(2), pp. 153-156

DOI


GaN/LiNbO3 (0001) interface formation calculated from first-principles

S. Sanna, W.G. Schmidt, Applied Surface Science (2010), 256, pp. 5740-5743

DOI


2009

Water adsorption on hydrogenated Si(111) surfaces

B. Lange, R. Posner, K. Pohl, C. Thierfelder, G. Grundmeier, S. Blankenburg, W.G. Schmidt, Surface Science (2009), 603, pp. 60-64

DOI


Rare-earth defect pairs in GaN: LDA+U calculations

S. Sanna, W.G. Schmidt, T. Frauenheim, U. Gerstmann, Physical Review B (2009), 80(10)

DOI


Vacancy clusters created via room temperature irradiation in 6H-SiC

A. Scholle, S. Greulich-Weber, E. Rauls, W.G. Schmidt, U. Gerstmann, Physica B: Condensed Matter (2009), 404, pp. 4742-4744

DOI


Structure of Si(111)-In Nanowires Determined from the Midinfrared Optical Response

S. Chandola, K. Hinrichs, M. Gensch, N. Esser, S. Wippermann, W.G. Schmidt, F. Bechstedt, K. Fleischer, J.F. McGilp, Physical Review Letters (2009), 102(22)

DOI


First-principles calculations of clean Au(110) surfaces and chemisorption of atomic oxygen

M. Landmann, E. Rauls, W.G. Schmidt, Physical Review B (2009), 79(4)

DOI


The physics of highly ordered molecular rows

S. Blankenburg, E. Rauls, W.G. Schmidt, physica status solidi (c) (2009), 7(2), pp. 153-156

DOI


Role of Dihydrogen Bonds for the Stabilization of Self-Assembled Molecular Nanostructures

S. Blankenburg, E. Rauls, W.G. Schmidt, The Journal of Physical Chemistry C (2009), 113, pp. 12653-12657

DOI


Dissociative and molecular adsorption of water onα-Al2O3(0001)

S. Wippermann, W.G. Schmidt, P. Thissen, G. Grundmeier, physica status solidi (c) (2009), 7(2), pp. 137-140

DOI


QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials

P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, G.L. Chiarotti, M. Cococcioni, I. Dabo, A. Dal Corso, S. de Gironcoli, S. Fabris, G. Fratesi, R. Gebauer, U. Gerstmann, C. Gougoussis, A. Kokalj, M. Lazzeri, L. Martin-Samos, N. Marzari, F. Mauri, R. Mazzarello, S. Paolini, A. Pasquarello, L. Paulatto, C. Sbraccia, S. Scandolo, G. Sclauzero, A.P. Seitsonen, A. Smogunov, P. Umari, R.M. Wentzcovitch, Journal of Physics: Condensed Matter (2009), 21(39)

DOI


Glutamic acid adsorbed on Ag(110): direct and indirect molecular interactions

S. Blankenburg, W.G. Schmidt, Journal of Physics: Condensed Matter (2009), 21

DOI


Water adsorption on the α-Al2O3(0001) surface

P. Thissen, G. Grundmeier, S. Wippermann, W.G. Schmidt, Physical Review B (2009), 80(24)

DOI


Ab initioinvestigation of the LiNbO3(0001) surface

S. Sanna, A.V. Gavrilenko, W.G. Schmidt, physica status solidi (c) (2009), 7(2), pp. 145-148

DOI


2008

LiNbO3ground- and excited-state properties from first-principles calculations

W.G. Schmidt, M. Albrecht, S. Wippermann, S. Blankenburg, E. Rauls, F. Fuchs, C. Rödl, J. Furthmüller, A. Hermann, Physical Review B (2008), 77

DOI


Resolving the Optical Spectrum of Water: Coordination and Electrostatic Effects

A. Hermann, W.G. Schmidt, P. Schwerdtfeger, Physical Review Letters (2008), 100(20)

DOI


Atomic structure and energetics of thec-GaN(001) surface

E. Rauls, S.J. Dijkstra, W.G. Schmidt, Physical Review B (2008), 78(11)

DOI


Theoretical study of the localization of excess electrons at the surface of ice

A. Hermann, P. Schwerdtfeger, W.G. Schmidt, Journal of Physics: Condensed Matter (2008), 20

DOI


Water adsorption on clean Ni(111) and p(2×2)-Ni(111)-O surfaces calculated from first principles

S. Wippermann, W.G. Schmidt, Physical Review B (2008), 78(23)

DOI


Adatom-Induced Conductance Modification of In Nanowires: Potential-Well Scattering and Structural Effects

S. Wippermann, N. Koch, W.G. Schmidt, Physical Review Letters (2008), 100(10)

DOI


Spatial modulation of molecular adsorption energies due to indirect interaction

S. Blankenburg, W.G. Schmidt, Physical Review B (2008), 78

DOI


Optical anisotropy of the In/Si(111)(4×1)/(8×2) nanowire array

S. Wippermann, W.G. Schmidt, Surface Science (2008), 603, pp. 247-250

DOI


DFT calculations of adenine adsorption on coin metal (110) surfaces

E. Rauls, S. Blankenburg, W.G. Schmidt, Surface Science (2008), 602, pp. 2170-2174

DOI


Ammonia adsorption on Cl/Si(001): First-principles calculations

B. Lange, W.G. Schmidt, Surface Science (2008), 602, pp. 1207-1211

DOI


Influence of the Side Group Aromaticity on the Organic Molecule Adsorption on Cu(110)

E. Rauls, W.G. Schmidt, Journal of Physical Chemistry C (2008), 112, pp. 11490-11494

DOI


2007

Hexagon versus Trimer Formation in In Nanowires on Si(111): Energetics and Quantum Conductance

A.A. Stekolnikov, K. Seino, F. Bechstedt, S. Wippermann, W.G. Schmidt, A. Calzolari, M.B. Nardelli, Physical Review Letters (2007), 98(2)

DOI


Ethanol adsorbed on ice: A first-principles study

C. Thierfelder, W.G. Schmidt, Physical Review B (2007), 76(19)

DOI


Long-Range Chiral Recognition due to Substrate Locking and Substrate-Adsorbate Charge Transfer

S. Blankenburg, W.G. Schmidt, Physical Review Letters (2007), 99(19)

DOI


Steric effects and chirality in the adsorption of glycine and phenylglycine on Cu(110)

S. Blankenburg, W.G. Schmidt, Nanotechnology (2007), 18

DOI


Quantum conductance of In nanowires on Si(111) from first principles calculations

S. Wippermann, W.G. Schmidt, A. Calzolari, M.B. Nardelli, A. Stekolnikov, K. Seino, F. Bechstedt, Surface Science (2007), pp. 4045-4047

DOI


2006

Strongly bonded water monomers on the ice Ih basal plane: Density-functional calculations

C. Thierfelder, A. Hermann, P. Schwerdtfeger, W.G. Schmidt, Physical Review B (2006), 74(4)

DOI


Adsorption of phenylglycine on copper: Density functional calculations

S. Blankenburg, W.G. Schmidt, Physical Review B (2006), 74(15)

DOI


Experimental and theoretical evidence for a hydrogen stabilizedc(2×2)reconstruction of the P-rich InP(001) surface

T. Letzig, F. Willig, P.H. Hahn, W.G. Schmidt, Physical Review B (2006), 74(24)

DOI


Adsorption of water on chlorine-terminated Si(111) from first principles: Substrate-induced ordering versus intermolecular interactions

S. Biering, A. Hermann, W.G. Schmidt, Physical Review B (2006), 73(23)

DOI


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