Prof. Dr. Uwe Gerstmann - Kontakt (Universität Paderborn)

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

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https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.6.105401

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

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

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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

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<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 VB– 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

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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

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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.

crystals-12-01586-v2.pdf - Creative Commons Attribution…

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

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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)

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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.

Impact of screening and relaxation on weakly coupled two-dimensional heterostructures

T.T.N. Nguyen, T. Sollfrank, C. Tegenkamp, E. Rauls, U. Gerstmann, Physical Review B (2021)

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Adsorption and Reaction of PbPc on Hydrogenated Epitaxial Graphene

D. Slawig, M. Gruschwitz, U. Gerstmann, E. Rauls, C. Tegenkamp, The Journal of Physical Chemistry C (2021), 125(36), pp. 20087-20093

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Hyperfine and nuclear quadrupole splitting of the NV− ground state in 4H-SiC

F.F. Murzakhanov, B.V. Yavkin, G.V. Mamin, S.B. Orlinskii, H.J. von Bardeleben, T. Biktagirov, U. Gerstmann, V.A. Soltamov, Physical Review B (2021), 103(24), 245203

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Impact of screening and relaxation on weakly coupled two-dimensional heterostructures

T.T.N. Nguyen, T. Sollfrank, C. Tegenkamp, E. Rauls, U. Gerstmann, Physical Review B (2021), 103(20), L201408

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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

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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)

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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

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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

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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

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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.

crystals-11-00542.pdf - Creative Commons Attribution…

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

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arXiv

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.

PhysRevB.104.174110.pdf - © 2021 American Physical…

Spin-orbit driven electrical manipulation of the zero-field splitting in high-spin centers in solids

T. Biktagirov, U. Gerstmann, Physical Review Research (2020), 2(2), 023071

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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

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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

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EPR spectroscopy reveals the universality class and dynamic effects of the [NH4][Zn(HCOO)3] hybrid formate framework.

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)

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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)

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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

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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

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

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

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Photochemical Ring Opening of Oxirane Modeled by Constrained Density Functional Theory

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

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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

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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.

PhysRevResearch.2.043002.pdf - Creative Commons Attribution…

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)

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Carbon vacancy-related centers in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>3</mml:mn><mml:mi>C</mml:mi></mml:math>-silicon carbide: Negative-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>U</mml:mi></mml:math> properties and structural transformation

H.J. von Bardeleben, E. Rauls, U. Gerstmann, Physical Review B (2020), 101(18), 184108

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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

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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, 022521

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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

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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

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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.

Neufeld_2019_J._Phys._Mater._2_045003.pdf - Creative Commons Attribution…

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

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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

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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)

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

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

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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

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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)

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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

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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

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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

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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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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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[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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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), 465901

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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

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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.

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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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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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

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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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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

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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)

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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)

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Lithium niobate dielectric function and second-order polarizability tensor from massively parallel ab initio calculations

A. Riefer, M. Rohrmüller, M. Landmann, S. Sanna, E. Rauls, N.J. Vollmers, R. Hölscher, M. Witte, Y. Li, U. Gerstmann, A. Schindlmayr, W.G. Schmidt, in: High Performance Computing in Science and Engineering ‘13, Springer, 2013, pp. 93-104

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The frequency-dependent dielectric function and the second-order polarizability tensor of ferroelectric LiNbO3 are calculated from first principles. The calculations are based on the electronic structure obtained from density-functional theory. The subsequent application of the GW approximation to account for quasiparticle effects and the solution of the Bethe–Salpeter equation yield a dielectric function for the stoichiometric material that slightly overestimates the absorption onset and the oscillator strength in comparison with experimental measurements. Calculations at the level of the independent-particle approximation indicate that these deficiencies are at least partially related to the neglect of intrinsic defects typical for the congruent material. The second-order polarizability calculated within the independent-particle approximation predicts strong nonlinear coefficients for photon energies above 1.5 eV. The comparison with measured data suggests that self-energy effects improve the agreement between experiment and theory. The intrinsic defects of congruent samples reduce the optical nonlinearities, in particular for the 21 and 31 tensor components, further improving the agreement with measured data.

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

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Electrically Detected Electron-Spin-Echo Envelope Modulation: A Highly Sensitive Technique for Resolving Complex Interface Structures

F. Hoehne, J. Lu, A.R. Stegner, M. Stutzmann, M.S. Brandt, M. Rohrmüller, W.G. Schmidt, U. Gerstmann, Physical Review Letters (2011), 106(19)

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Microscopic structure and energy transfer of vacancy-related defect pairs with Erbium in wide-gap semiconductors

A. Konopka, S. Greulich-Weber, V. Dierolf, H. Jiang, U. Gerstmann, E. Rauls, S. Sanna, W.G. Schmidt, Optical Materials (2011), 33, pp. 1041-1044

DOI

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

Manganese-hydrogen complexes inGa1−xMnxN

C. Bihler, U. Gerstmann, M. Hoeb, T. Graf, M. Gjukic, W.G. Schmidt, M. Stutzmann, M.S. Brandt, Physical Review B (2010), 80(20)

DOI

Magnetic characterization of conductance electrons in GaN

A. Scholle, S. Greulich-Weber, D.J. As, C. Mietze, N.T. Son, C. Hemmingsson, B. Monemar, E. Janzén, U. Gerstmann, S. Sanna, E. Rauls, W.G. Schmidt, physica status solidi (b) (2010), 247(7), pp. 1728-1731

DOI

Fine Structure of Triplet Centers in Room Temperature Irradiated 6H-SiC

A. Scholle, S. Greulich-Weber, E. Rauls, W.G. Schmidt, U. Gerstmann, Materials Science Forum (2010), 645-648, pp. 403-406

Abstract

DOI

<jats:p>In non-annealed 6H-SiC samples that were electron irradiated at room temperature, a new EPR signal due to a S=1 defect center with exceptionally large zero-field splitting (D = +652•10-4 cm-1) has been observed under illumination. A positive sign of D demonstrates that the spin-orbit contribution to the zero-field splitting exceeds by far that of the spin-spin interaction. A principal axis of the fine structure tilted by 59° against the crystal c-axis as well as the exceptionally high zero-field splitting D can be qualitatively understood by the occurrence of additional close-lying defect levels in defect clusters resulting in comparatively large second-order spin-orbit coup¬ling. A tentative assignment to vacancy clusters is supported by the observed annealing behavior. </jats:p>

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

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

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), 395502

DOI

Spin-Coupling in Heavily Nitrogen-Doped 4H-SiC

D. Savchenko, A. Pöppl, E.N. Kalabukhova, S. Greulich-Weber, E. Rauls, W.G. Schmidt, U. Gerstmann, Materials Science Forum (2009), 615-617, pp. 343-346

Abstract

DOI

<jats:p>EPR and ESE in nitrogen doped 4H- and 6H-SiC show besides the well known triplet lines of 14N on quasi-cubic (Nc,k) and hexagonal (Nc,h) sites additional lines (Nx) of comparatively low intensity providing half the hf splitting of Nc,k. Frequently re-interpreted as spin-forbid¬den lines, arising from Nc,k pairs and triads or resulting from hopping conductivity, only re¬cent¬ly the theoretical calculation of the corresponding g-tensors lead to a tentative model of distant NC donor pairs on inequivalent lattice sites which are coupled to S = 1 assuming a fine-struc¬ture splitting too small to be observed in the EPR and ESE experiments. In this work, we pre¬sent ESE nutation measurements confirming S = 1 for the Nx center. Analysing the nutation frequencies in comparison with that of the Nc,k (S = 1/2) spectrum as well as the line width of ESE and EPR spectra we obtain a rough estimate between 5104 cm-1 and 50104 cm-1 for the fine-structure splitting demonstrating efficient spin-coupling between nitrogen donors in 4H-SiC.</jats:p>