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Data Center Building O

Prof. Dr. Wolf Gero Schmidt

Contact
Biography
Publications
Prof. Dr. Wolf Gero Schmidt

Fakultät für Naturwissenschaften

Dean - Professor

Phone:
+49 5251 60-2679
Fax:
+49 5251 60-3216

Theoretical Materials Physics

Head - Professor - Lehrstuhlinhaber

Center for Optoelectronics and Photonics (CeOPP)

Committee - Professor

Vorstand

Member - Professor

Phone:
+49 5251 60-2335
Phone:
05251/60-2677
Fax:
+49 5251 60-3435
Office:
N3.347
Visitor:
Pohlweg 55
33098 Paderborn
Prof. Dr. Wolf Gero Schmidt
2018 - today

Dean of the Faculty of Science

2016 - 2018

Vice Dean of the Faculty of Science

2010

Chair offer (W3) from Bielefeld Univ, declined

2006

Full Prof (W3) in theoretical physics, Paderborn Univ

2005

Assoc Prof, Massey Univ, New Zealand

2002

Habilitation, Jena Univ

2001

Adjunct Assistant Prof, North Carolina State Univ, USA

1997 - 1999

Postdoctoral fellow with J Bernholc, NC State U, USA

1997

PhD in physics with Friedhelm Bechstedt, Jena Univ

1994

Visiting researcher with WS Verwoerd, University of South Africa

1993

Visiting researcher with GP Srivastava, Exeter Univ, UK

1988 - 1993

Diploma studies in physics, Jena Univ


Open list in Research Information System

2022

Clean and Hydrogen‐Adsorbed AlInP(001) Surfaces: Structures and Electronic Properties

L.J. Glahn, I.A. Ruiz Alvarado, S. Neufeld, M.A. Zare Pour, A. Paszuk, D. Ostheimer, S. Shekarabi, O. Romanyuk, D.C. Moritz, J.P. Hofmann, W. Jaegermann, T. Hannappel, W.G. Schmidt, physica status solidi (b) (2022), 259(11), 2200308

DOI


P-Terminated InP (001) Surfaces: Surface Band Bending and Reactivity to Water

D.C. Moritz, I.A. Ruiz Alvarado, M.A. Zare Pour, A. Paszuk, T. Frieß, E. Runge, J.P. Hofmann, T. Hannappel, W.G. Schmidt, W. Jaegermann, ACS Applied Materials & Interfaces (2022), 14(41), pp. 47255-47261

DOI


Electrochemical performance of $\mathrmKTiOAsO_4$ (KTA) in potassium-ion batteries from density-functional theory

A. Bocchini, U. Gerstmann, T. Bartley, H. Steinrück, G. Henkel, W.G. Schmidt, Phys. Rev. Materials (2022), 6, pp. 105401


Oxygen vacancies in $\mathrmKTiOPO_4$: Optical absorption from hybrid DFT

A. Bocchini, U. Gerstmann, W.G. Schmidt, Phys. Rev. B (2022), 105, pp. 205118

DOI


Bound polaron formation in lithium niobate from ab initio molecular dynamics

M. Krenz, U. Gerstmann, W.G. Schmidt, Applied Physics A (2022), 128(6), 480

<jats:title>Abstract</jats:title><jats:p>Polarons influence decisively the performance of lithium niobate for optical applications. In this work, the formation of (defect) bound polarons in lithium niobate is studied by ab initio molecular dynamics. The calculations show a broad scatter of polaron formation times. Rising temperature increases the share of trajectories with long formation times, which leads to an overall increase of the average formation time with temperature. However, even at elevated temperatures, the average formation time does not exceed the value of 100 femtoseconds, i.e., a value close to the time measured for free, i.e., self-trapped polarons. Analyzing individual trajectories, it is found that the time required for the structural relaxation of the polarons depends sensitively on the excitation of the lithium niobate high-frequency phonon modes and their phase relation.</jats:p>


Electron–Nuclear Coherent Coupling and Nuclear Spin Readout through Optically Polarized V<sub>B</sub><sup>–</sup> Spin States in hBN

F.F. Murzakhanov, G.V. Mamin, S.B. Orlinskii, U. Gerstmann, W.G. Schmidt, T. Biktagirov, I. Aharonovich, A. Gottscholl, A. Sperlich, V. Dyakonov, V.A. Soltamov, Nano Letters (2022), 22(7), pp. 2718-2724

DOI


Water/InP(001) from Density Functional Theory

I.A. Ruiz Alvarado, W.G. Schmidt, ACS Omega (2022), 7(23), pp. 19355-19364

DOI


Reconstructions of the As-Terminated GaAs(001) Surface Exposed to Atomic Hydrogen

M. Karmo, I.A. Ruiz Alvarado, W.G. Schmidt, E. Runge, ACS Omega (2022), 7(6), pp. 5064-5068

DOI


Quasiparticle energies and optical response of RbTiOPO4 and KTiOAsO4

S. Neufeld, A. Schindlmayr, W.G. Schmidt, Journal of Physics: Materials (2022), 5(1), 015002

Many-body perturbation theory based on density-functional theory calculations is used to determine the quasiparticle band structures and the dielectric functions of the isomorphic ferroelectrics rubidium titanyl phosphate (RbTiOPO4) and potassium titanyl arsenide (KTiOAsO4). Self-energy corrections of more than 2 eV are found to widen the transport band gaps of both materials considerably to 5.3 and 5.2 eV, respectively. At the same time, both materials are characterized by strong exciton binding energies of 1.4 and 1.5 eV, respectively. The solution of the Bethe-Salpeter equation based on the quasiparticle energies results in onsets of the optical absorption within the range of the measured data.


A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate

F. Schmidt, A.L. Kozub, U. Gerstmann, W.G. Schmidt, A. Schindlmayr, Crystals (2022), 12(11), 1586

Hole polarons and defect-bound exciton polarons in lithium niobate are investigated by means of density-functional theory, where the localization of the holes is achieved by applying the +U approach to the oxygen 2p orbitals. We find three principal configurations of hole polarons: (i) self-trapped holes localized at displaced regular oxygen atoms and (ii) two other configurations bound to a lithium vacancy either at a threefold coordinated oxygen atom above or at a twofold coordinated oxygen atom below the defect. The latter is most stable and in excellent quantitative agreement with measured g factors from electron paramagnetic resonance. Due to the absence of mid-gap states, none of these hole polarons can explain the broad optical absorption centered between 2.5 and 2.8 eV that is observed in transient absorption spectroscopy, but such states appear if a free electron polaron is trapped at the same lithium vacancy as the bound hole polaron, resulting in an exciton polaron. The dielectric function calculated by solving the Bethe-Salpeter equation indeed yields an optical peak at 2.6 eV in agreement with the two-photon experiments. The coexistence of hole and exciton polarons, which are simultaneously created in optical excitations, thus satisfactorily explains the reported experimental data.


Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response

F. Schmidt, A.L. Kozub, U. Gerstmann, W.G. Schmidt, A. Schindlmayr, in: New Trends in Lithium Niobate: From Bulk to Nanocrystals, MDPI, 2022, pp. 231-248

Lithium niobate (LiNbO3), a material frequently used in optical applications, hosts different kinds of polarons that significantly affect many of its physical properties. In this study, a variety of electron polarons, namely free, bound, and bipolarons, are analyzed using first-principles calculations. We perform a full structural optimization based on density-functional theory for selected intrinsic defects with special attention to the role of symmetry-breaking distortions that lower the total energy. The cations hosting the various polarons relax to a different degree, with a larger relaxation corresponding to a larger gap between the defect level and the conduction-band edge. The projected density of states reveals that the polaron states are formerly empty Nb 4d states lowered into the band gap. Optical absorption spectra are derived within the independent-particle approximation, corrected by the GW approximation that yields a wider band gap and by including excitonic effects within the Bethe-Salpeter equation. Comparing the calculated spectra with the density of states, we find that the defect peak observed in the optical absorption stems from transitions between the defect level and a continuum of empty Nb 4d states. Signatures of polarons are further analyzed in the reflectivity and other experimentally measurable optical coefficients.


DC Ionic Conductivity in KTP and Its Isomorphs: Properties, Methods for Suppression, and Its Connection to Gray Tracking

L. Padberg, V. Quiring, A. Bocchini, M. Santandrea, U. Gerstmann, W.G. Schmidt, C. Silberhorn, C. Eigner, Crystals (2022), 12(10)

We study the DC conductivity in potassium titanyl phosphate (KTiOPO4, KTP) and its isomorphs KTiOAsO4 (KTA) and Rb1%K99%TiOPO4 (RKTP) and introduce a method by which to reduce the overall ionic conductivity in KTP by a potassium nitrate treatment. Furthermore, we create so-called gray tracking in KTP and investigate the ionic conductivity in theses areas. A local unintended reduction of the ionic conductivity is observed in the gray-tracked regions, which also induce additional optical absorption in the material. We show that a thermal treatment in an oxygen-rich atmosphere removes the gray tracking and brings the ionic conductivity as well as the optical transmission back to the original level. These studies can help to choose the best material and treatment for specific applications.


2021

Controlled growth of ordered monolayers of N-heterocyclic carbenes on silicon

M. Franz, S. Chandola, M. Koy, R. Zielinski, H. Aldahhak, M. Das, M. Freitag, U. Gerstmann, D. Liebig, A.K. Hoffmann, M. Rosin, W.G. Schmidt, C. Hogan, F. Glorius, N. Esser, M. Dähne, Nature Chemistry (2021), pp. 828-835

DOI


Electronic structure of the Si(111)3×3R30∘−B surface from theory and photoemission spectroscopy

H. Aldahhak, C. Hogan, S. Lindner, S. Appelfeller, H. Eisele, W.G. Schmidt, M. Dähne, U. Gerstmann, M. Franz, Physical Review B (2021)

DOI


Spin Polarization, Electron–Phonon Coupling, and Zero-Phonon Line of the NV Center in 3C-SiC

H. Jurgen von Bardeleben, J. Cantin, U. Gerstmann, W.G. Schmidt, T. Biktagirov, Nano Letters (2021), 21(19), pp. 8119-8125

DOI


Surface localized phonon modes at the Si(553)-Au nanowire system

J. Plaickner, E. Speiser, C. Braun, W.G. Schmidt, N. Esser, S. Sanna, Physical Review B (2021)

DOI


InP and AlInP(001)(2 × 4) Surface Oxidation from Density Functional Theory

I.A. Ruiz Alvarado, M. Karmo, E. Runge, W.G. Schmidt, ACS Omega (2021), pp. 6297-6304

DOI


Adatom mediated adsorption of <scp>N‐heterocyclic</scp> carbenes on Cu(111) and Au(111)

M. Jain, U. Gerstmann, W.G. Schmidt, H. Aldahhak, Journal of Computational Chemistry (2021), 43(6), pp. 413-420

DOI


Potassium titanyl phosphate Z- and Y-cut surfaces from density-functional theory

S. Neufeld, A. Bocchini, W.G. Schmidt, Physical Review Materials (2021)

DOI


Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response

F. Schmidt, A.L. Kozub, U. Gerstmann, W.G. Schmidt, A. Schindlmayr, Crystals (2021), 11(5), 542

Lithium niobate (LiNbO3), a material frequently used in optical applications, hosts different kinds of polarons that significantly affect many of its physical properties. In this study, a variety of electron polarons, namely free, bound, and bipolarons, are analyzed using first-principles calculations. We perform a full structural optimization based on density-functional theory for selected intrinsic defects with special attention to the role of symmetry-breaking distortions that lower the total energy. The cations hosting the various polarons relax to a different degree, with a larger relaxation corresponding to a larger gap between the defect level and the conduction-band edge. The projected density of states reveals that the polaron states are formerly empty Nb 4d states lowered into the band gap. Optical absorption spectra are derived within the independent-particle approximation, corrected by the GW approximation that yields a wider band gap and by including excitonic effects within the Bethe-Salpeter equation. Comparing the calculated spectra with the density of states, we find that the defect peak observed in the optical absorption stems from transitions between the defect level and a continuum of empty Nb 4d states. Signatures of polarons are further analyzed in the reflectivity and other experimentally measurable optical coefficients.


Polaronic enhancement of second-harmonic generation in lithium niobate

A.L. Kozub, A. Schindlmayr, U. Gerstmann, W.G. Schmidt, Physical Review B (2021), 104(17), 174110

Density-functional theory within a Berry-phase formulation of the dynamical polarization is used to determine the second-order susceptibility χ(2) of lithium niobate (LiNbO3). Defect trapped polarons and bipolarons are found to strongly enhance the nonlinear susceptibility of the material, in particular if localized at NbV–VLi defect pairs. This is essentially a consequence of the polaronic excitation resulting in relaxation-induced gap states. The occupation of these levels leads to strongly enhanced χ(2) coefficients and allows for the spatial and transient modification of the second-harmonic generation of macroscopic samples.


GaInP/AlInP(001) Interfaces from Density Functional Theory

L. Meier, W.G. Schmidt, physica status solidi (b) (2021), 259(1), 2100462

DOI


2020

Understanding gray track formation in KTP: $\mathrmTi^3+$ centers studied from first principles

A. Bocchini, C. Eigner, C. Silberhorn, W.G. Schmidt, U. Gerstmann, Phys. Rev. Materials (2020), 4, pp. 124402

DOI


Electron paramagnetic resonance study of ferroelectric phase transition and dynamic effects in a Mn2+ doped [NH4][Zn(HCOO)3] hybrid formate framework

M. Navickas, L. Giriūnas, V. Kalendra, T. Biktagirov, U. Gerstmann, W.G. Schmidt, M. Mączka, A. Pöppl, J. Banys, M. Šimėnas, Physical Chemistry Chemical Physics (2020), 22, pp. 8513-8521

<p>EPR spectroscopy reveals the universality class and dynamic effects of the [NH<sub>4</sub>][Zn(HCOO)<sub>3</sub>] hybrid formate framework.</p>


Vibration-Driven Self-Doping of Dangling-Bond Wires on Si(553)-Au Surfaces

C. Braun, S. Neufeld, U. Gerstmann, S. Sanna, J. Plaickner, E. Speiser, N. Esser, W.G. Schmidt, Physical Review Letters (2020), 124(14)

DOI


Spin decontamination for magnetic dipolar coupling calculations: Application to high-spin molecules and solid-state spin qubits

T. Biktagirov, W.G. Schmidt, U. Gerstmann, Physical Review Research (2020)

DOI


Tetracene Ultrathin Film Growth on Hydrogen-Passivated Silicon

J. Niederhausen, R.W. MacQueen, K. Lips, H. Aldahhak, W.G. Schmidt, U. Gerstmann, Langmuir (2020), pp. 9099-9113

DOI


A photoredox catalysed Heck reaction via hole transfer from a Ru(ii)-bis(terpyridine) complex to graphene oxide

M. Rosenthal, J. Lindner, U. Gerstmann, A. Meier, W.G. Schmidt, R. Wilhelm, RSC Advances (2020), 10(70), pp. 42930-42937

<p>A hole transfer from an excited Ru unit towards graphene oxide significantly improved the photocatalytic activity of the complexes.</p>


Toward Efficient Toxic-Gas Detectors: Exploring Molecular Interactions of Sarin and Dimethyl Methylphosphonate with Metal-Centered Phthalocyanine Structures

H. Aldahhak, P. Powroźnik, P. Pander, W. Jakubik, F.B. Dias, W.G. Schmidt, U. Gerstmann, M. Krzywiecki, The Journal of Physical Chemistry C (2020)(124), pp. 6090-6102

DOI


Vibrational Raman spectroscopy on adsorbate-induced low-dimensional surface structures

E. Speiser, N. Esser, B. Halbig, J. Geurts, W.G. Schmidt, S. Sanna, Surface Science Reports (2020), 75(1), 100480

DOI


Photocatalytic properties of graphene‐supported titania clusters from density‐functional theory

S. Badalov, R. Wilhelm, W.G. Schmidt, Journal of Computational Chemistry (2020), pp. 1921-1930

DOI


Photochemical Ring Opening of Oxirane Modeled by Constrained Density Functional Theory

M. Krenz, U. Gerstmann, W.G. Schmidt, ACS Omega (2020), pp. 24057-24063

DOI


Band Alignment at Ga <sub> <i>x</i> </sub> In <sub> 1– <i>x</i> </sub> P/Al <sub> <i>y</i> </sub> In <sub> 1– <i>y</i> </sub> P Alloy Interfaces from Hybrid Density Functional Theory Calculations

L. Meier, C. Braun, T. Hannappel, W.G. Schmidt, physica status solidi (b) (2020), 258(2), 2000463

DOI


Free and defect-bound (bi)polarons in LiNbO3: Atomic structure and spectroscopic signatures from ab initio calculations

F. Schmidt, A.L. Kozub, T. Biktagirov, C. Eigner, C. Silberhorn, A. Schindlmayr, W.G. Schmidt, U. Gerstmann, Physical Review Research (2020), 2(4), 043002

Polarons in dielectric crystals play a crucial role for applications in integrated electronics and optoelectronics. In this work, we use density-functional theory and Green's function methods to explore the microscopic structure and spectroscopic signatures of electron polarons in lithium niobate (LiNbO3). Total-energy calculations and the comparison of calculated electron paramagnetic resonance data with available measurements reveal the formation of bound polarons at Nb_Li antisite defects with a quasi-Jahn-Teller distorted, tilted configuration. The defect-formation energies further indicate that (bi)polarons may form not only at Nb_Li antisites but also at structures where the antisite Nb atom moves into a neighboring empty oxygen octahedron. Based on these structure models, and on the calculated charge-transition levels and potential-energy barriers, we propose two mechanisms for the optical and thermal splitting of bipolarons, which provide a natural explanation for the reported two-path recombination of bipolarons. Optical-response calculations based on the Bethe-Salpeter equation, in combination with available experimental data and new measurements of the optical absorption spectrum, further corroborate the geometries proposed here for free and defect-bound (bi)polarons.


Spin decontamination for magnetic dipolar coupling calculations: Application to high-spin molecules and solid-state spin qubits

T. Biktagirov, W.G. Schmidt, U. Gerstmann, Physical Review Research (2020), 2(2)

DOI


2019

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), 3(5), 054401

The cubic, tetragonal, and orthorhombic phase of potassium niobate (KNbO3) are studied based on density-functional theory. Starting from the relaxed atomic geometries, we analyze the influence of self-energy corrections on the electronic band structure within the GW approximation. We find that quasiparticle shifts widen the direct (indirect) band gap by 1.21 (1.44), 1.58 (1.55), and 1.67 (1.64) eV for the cubic, tetragonal, and orthorhombic phase, respectively. By solving the Bethe-Salpeter equation, we obtain the linear dielectric function with excitonic and local-field effects, which turn out to be essential for good agreement with experimental data. From our results, we extract an exciton binding energy of 0.6, 0.5, and 0.5 eV for the cubic, tetragonal, and orthorhombic phase, respectively. Furthermore, we investigate the nonlinear second-harmonic generation (SHG) both theoretically and experimentally. The frequency-dependent second-order polarization tensor of orthorhombic KNbO3 is measured for incoming photon energies between 1.2 and 1.6 eV. In addition, calculations within the independent-(quasi)particle approximation are performed for the tetragonal and orthorhombic phase. The novel experimental data are in excellent agreement with the quasiparticle calculations and resolve persistent discrepancies between earlier experimental measurements and ab initio results reported in the literature.


Water Splitting Reaction at Polar Lithium Niobate Surfaces

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

DOI


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), 385401

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), 2(4), 045003

The KTiOPO4 (KTP) band structure and dielectric function are calculated on various levels of theory starting from density-functional calculations. Within the independent-particle approximation an electronic transport gap of 2.97 eV is obtained that widens to about 5.23 eV when quasiparticle effects are included using the GW approximation. The optical response is shown to be strongly anisotropic due to (i) the slight asymmetry of the TiO6 octahedra in the (001) plane and (ii) their anisotropic distribution along the [001] and [100] directions. In addition, excitonic effects are very important: The solution of the Bethe–Salpeter equation indicates exciton binding energies of the order of 1.5 eV. Calculations that include both quasiparticle and excitonic effects are in good agreement with the measured reflectivity.


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), 155107

DOI


2018

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


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

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

DOI


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


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


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>


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


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), 019902


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


Temperature stabilizes rough Au/Ge(001) surface reconstructions

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

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>


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


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


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)(256), 1800314

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, 2890

DOI


2017

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), 29(21), 215702

The electronic band structures of hexagonal ZnO and cubic ZnS, ZnSe, and ZnTe compounds are determined within hybrid-density-functional theory and quasiparticle calculations. It is found that the band-edge energies calculated on the G0W0 (Zn chalcogenides) or GW (ZnO) level of theory agree well with experiment, while fully self-consistent QSGW calculations are required for the correct description of the Zn 3d bands. The quasiparticle band structures are used to calculate the linear response and second-harmonic-generation (SHG) spectra of the Zn–VI compounds. Excitonic effects in the optical absorption are accounted for within the Bethe–Salpeter approach. The calculated spectra are discussed in the context of previous experimental data and present SHG measurements for ZnO.


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


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


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


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), 054406

The optical properties of congruent lithium niobate are analyzed from first principles. The dielectric function of the material is calculated within time-dependent density-functional theory. The effects of isolated intrinsic defects and defect pairs, including the NbLi4+ antisite and the NbLi4+−NbNb4+ pair, commonly addressed as a bound polaron and bipolaron, respectively, are discussed in detail. In addition, we present further possible realizations of polaronic and bipolaronic systems. The absorption feature around 1.64 eV, ascribed to small bound polarons [O. F. Schirmer et al., J. Phys.: Condens. Matter 21, 123201 (2009)], is nicely reproduced within these models. Among the investigated defects, we find that the presence of bipolarons at bound interstitial-vacancy pairs NbV−VLi can best explain the experimentally observed broad absorption band at 2.5 eV. Our results provide a microscopic model for the observed optical spectra and suggest that, besides NbLi antisites and Nb and Li vacancies, Nb interstitials are also formed in congruent lithium-niobate samples.


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

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LiNbO3 surfaces from a microscopic perspective

S. Sanna, W.G. Schmidt, Journal of Physics: Condensed Matter (2017), 413001

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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

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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

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[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

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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

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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

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Electron paramagnetic resonance calculations for hydrogenated Si surfaces

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

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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)

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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

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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)

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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), 1(3), 034401

The optical properties of pristine and titanium-doped LiNbO3 are modeled from first principles. The dielectric functions are calculated within time-dependent density-functional theory, and a model long-range contribution is employed for the exchange-correlation kernel in order to account for the electron-hole binding. Our study focuses on the influence of substitutional titanium atoms on lithium sites. We show that an increasing titanium concentration enhances the values of the refractive indices and the reflectivity.


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), 2017, 3981317

We perform a comprehensive theoretical study of the structural and electronic properties of potassium niobate (KNbO3) 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 KNbO3. 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.


2016

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)

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LiNbO3 electronic 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), 93(7), 075205

The influence of electronic many-body interactions, spin-orbit coupling, and thermal lattice vibrations on the electronic structure of lithium niobate is calculated from first principles. Self-energy calculations in the GW approximation show that the inclusion of self-consistency in the Green function G and the screened Coulomb potential W opens the band gap far stronger than found in previous G0W0 calculations but slightly overestimates its actual value due to the neglect of excitonic effects in W. A realistic frozen-lattice band gap of about 5.9 eV is obtained by combining hybrid density functional theory with the QSGW0 scheme. The renormalization of the band gap due to electron-phonon coupling, derived here using molecular dynamics as well as density functional perturbation theory, reduces this value by about 0.5 eV at room temperature. Spin-orbit coupling does not noticeably modify the fundamental gap but gives rise to a Rashba-like spin texture in the conduction band.


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

The phonon dispersions of the ferro‐ and paraelectric phase of LiTaO3 are calculated within density‐functional perturbation theory. The longitudinal optical phonon modes are theoretically derived and compared with available experimental data. Our results confirm the recent phonon assignment proposed by Margueron et al. [J. Appl. Phys. 111, 104105 (2012)] on the basis of spectroscopical studies. A comparison with the phonon band structure of the related material LiNbO3 shows minor differences that can be traced to the atomic‐mass difference between Ta and Nb. The presence of phonons with imaginary frequencies for the paraelectric phase suggests that it does not correspond to a minimum energy structure, and is compatible with an order‐disorder type phase transition.


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)

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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

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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

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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)

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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

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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

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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)

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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)

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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)

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A Bifunctional Electrocatalyst for Oxygen Evolution and Oxygen Reduction Reactions in Water

W. Schöfberger, F. Faschinger, S. Chattopadhyay, S. Bhakta, B. Mondal, J.A.A.W. Elemans, S. Müllegger, S. Tebi, R. Koch, F. Klappenberger, M. Paszkiewicz, J.V. Barth, E. Rauls, H. Aldahhak, W.G. Schmidt, A. Dey, Angewandte Chemie International Edition (2016), pp. 2350-2355

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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, 025704

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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>


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

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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)

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2015

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)

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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

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Phonon dispersion and zero-point renormalization of LiNbO3 from density-functional perturbation theory

M. Friedrich, A. Riefer, S. Sanna, W.G. Schmidt, A. Schindlmayr, Journal of Physics: Condensed Matter (2015), 27(38), 385402

The vibrational properties of stoichiometric LiNbO3 are analyzed within density-functional perturbation theory in order to obtain the complete phonon dispersion of the material. The phonon density of states of the ferroelectric (paraelectric) phase shows two (one) distinct band gaps separating the high-frequency (~800 cm−1) optical branches from the continuum of acoustic and lower optical phonon states. This result leads to specific heat capacites in close agreement with experimental measurements in the range 0–350 K and a Debye temperature of 574 K. The calculated zero-point renormalization of the electronic Kohn–Sham eigenvalues reveals a strong dependence on the phonon wave vectors, especially near Γ. Integrated over all phonon modes, our results indicate a vibrational correction of the electronic band gap of 0.41 eV at 0 K, which is in excellent agreement with the extrapolated temperature-dependent measurements.


Defect complexes in congruentLiNbO3and their optical signatures

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

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Raman scattering efficiency inLiTaO3andLiNbO3crystals

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

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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

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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)

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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

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

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

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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)

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