TY - JOUR AB - A series of new organic donor–π–acceptor dyes incorporating a diquat moiety as a novel electron-acceptor unit have been synthesized and characterized. The analytical data were supported by DFT calculations. These dyes were explored in the aerobic thiocyanation of indoles and pyrroles. Here they showed a high photocatalytic activity under visible light, giving isolated yields of up to 97 %. In addition, the photocatalytic activity of standalone diquat and methyl viologen through formation of an electron donor acceptor complex is presented. AU - Meier, Armin AU - Badalov, Sabuhi AU - Biktagirov, Timur AU - Schmidt, Wolf Gero AU - Wilhelm, René ID - 43827 IS - 22 JF - Chemistry – A European Journal KW - General Chemistry KW - Catalysis KW - Organic Chemistry SN - 0947-6539 TI - Diquat Based Dyes: A New Class of Photoredox Catalysts and Their Use in Aerobic Thiocyanation VL - 29 ER - TY - JOUR AU - Ruiz Alvarado, Isaac Azahel AU - Zare Pour, Mohammad Amin AU - Hannappel, Thomas AU - Schmidt, Wolf Gero ID - 49634 IS - 4 JF - Physical Review B SN - 2469-9950 TI - Structural fingerprints in the reflectance anisotropy of AlInP(001) VL - 108 ER - TY - CHAP AB - 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. AU - Schmidt, Falko AU - Kozub, Agnieszka L. AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero AU - Schindlmayr, Arno ED - Corradi, Gábor ED - Kovács, László ID - 30288 SN - 978-3-0365-3340-7 T2 - New Trends in Lithium Niobate: From Bulk to Nanocrystals TI - Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response ER - TY - JOUR AB - AbstractPolarons 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. AU - Krenz, Marvin AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero ID - 37711 JF - Applied Physics A KW - General Materials Science KW - General Chemistry SN - 0947-8396 TI - Bound polaron formation in lithium niobate from ab initio molecular dynamics VL - 128 ER - TY - JOUR AB - 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. AU - Padberg, Laura AU - Quiring, Viktor AU - Bocchini, Adriana AU - Santandrea, Matteo AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero AU - Silberhorn, Christine AU - Eigner, Christof ID - 33484 JF - Crystals SN - 2073-4352 TI - DC Ionic Conductivity in KTP and Its Isomorphs: Properties, Methods for Suppression, and Its Connection to Gray Tracking VL - 12 ER - TY - JOUR AB - 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. AU - Neufeld, Sergej AU - Schindlmayr, Arno AU - Schmidt, Wolf Gero ID - 26627 IS - 1 JF - Journal of Physics: Materials TI - Quasiparticle energies and optical response of RbTiOPO4 and KTiOAsO4 VL - 5 ER - TY - JOUR AU - Glahn, Luis Joel AU - Ruiz Alvarado, Isaac Azahel AU - Neufeld, Sergej AU - Zare Pour, Mohammad Amin AU - Paszuk, Agnieszka AU - Ostheimer, David AU - Shekarabi, Sahar AU - Romanyuk, Oleksandr AU - Moritz, Dominik Christian AU - Hofmann, Jan Philipp AU - Jaegermann, Wolfram AU - Hannappel, Thomas AU - Schmidt, Wolf Gero ID - 37656 IS - 11 JF - physica status solidi (b) KW - Condensed Matter Physics KW - Electronic KW - Optical and Magnetic Materials SN - 0370-1972 TI - Clean and Hydrogen‐Adsorbed AlInP(001) Surfaces: Structures and Electronic Properties VL - 259 ER - TY - JOUR AU - Ruiz Alvarado, Isaac Azahel AU - Schmidt, Wolf Gero ID - 37710 IS - 23 JF - ACS Omega KW - General Chemical Engineering KW - General Chemistry SN - 2470-1343 TI - Water/InP(001) from Density Functional Theory VL - 7 ER - TY - JOUR AU - Moritz, Dominik Christian AU - Ruiz Alvarado, Isaac Azahel AU - Zare Pour, Mohammad Amin AU - Paszuk, Agnieszka AU - Frieß, Tilo AU - Runge, Erich AU - Hofmann, Jan P. AU - Hannappel, Thomas AU - Schmidt, Wolf Gero AU - Jaegermann, Wolfram ID - 37681 IS - 41 JF - ACS Applied Materials & Interfaces KW - General Materials Science SN - 1944-8244 TI - P-Terminated InP (001) Surfaces: Surface Band Bending and Reactivity to Water VL - 14 ER - TY - JOUR AU - Karmo, Marsel AU - Ruiz Alvarado, Isaac Azahel AU - Schmidt, Wolf Gero AU - Runge, Erich ID - 37714 IS - 6 JF - ACS Omega KW - General Chemical Engineering KW - General Chemistry SN - 2470-1343 TI - Reconstructions of the As-Terminated GaAs(001) Surface Exposed to Atomic Hydrogen VL - 7 ER - TY - JOUR AU - Murzakhanov, Fadis F. AU - Mamin, Georgy Vladimirovich AU - Orlinskii, Sergei Borisovich AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero AU - Biktagirov, Timur AU - Aharonovich, Igor AU - Gottscholl, Andreas AU - Sperlich, Andreas AU - Dyakonov, Vladimir AU - Soltamov, Victor A. ID - 37713 IS - 7 JF - Nano Letters KW - Mechanical Engineering KW - Condensed Matter Physics KW - General Materials Science KW - General Chemistry KW - Bioengineering SN - 1530-6984 TI - Electron–Nuclear Coherent Coupling and Nuclear Spin Readout through Optically Polarized VB Spin States in hBN VL - 22 ER - TY - JOUR AU - Bocchini, Adriana AU - Gerstmann, Uwe AU - Bartley, Tim AU - Steinrück, Hans-Georg AU - Henkel, Gerald AU - Schmidt, Wolf Gero ID - 33965 JF - Phys. Rev. Materials TI - Electrochemical performance of KTiOAsO_4 (KTA) in potassium-ion batteries from density-functional theory VL - 6 ER - TY - JOUR AU - Bocchini, Adriana AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero ID - 31254 JF - Phys. Rev. B TI - Oxygen vacancies in KTiOPO_4: Optical absorption from hybrid DFT VL - 105 ER - TY - JOUR AB - 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 two-fold coordinated oxygen atom below the defect. The latter is the most stable and is 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. AU - Schmidt, Falko AU - Kozub, Agnieszka L. AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero AU - Schindlmayr, Arno ID - 44088 IS - 11 JF - Crystals TI - A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate VL - 12 ER - TY - JOUR AU - Jurgen von Bardeleben, Hans AU - Cantin, Jean-Louis AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero AU - Biktagirov, Timur ID - 29747 IS - 19 JF - Nano Letters KW - Mechanical Engineering KW - Condensed Matter Physics KW - General Materials Science KW - General Chemistry KW - Bioengineering SN - 1530-6984 TI - Spin Polarization, Electron–Phonon Coupling, and Zero-Phonon Line of the NV Center in 3C-SiC VL - 21 ER - TY - JOUR AU - Slawig, Diana AU - Gruschwitz, Markus AU - Gerstmann, Uwe AU - Rauls, Eva AU - Tegenkamp, Christoph ID - 29748 IS - 36 JF - The Journal of Physical Chemistry C KW - Surfaces KW - Coatings and Films KW - Physical and Theoretical Chemistry KW - General Energy KW - Electronic KW - Optical and Magnetic Materials SN - 1932-7447 TI - Adsorption and Reaction of PbPc on Hydrogenated Epitaxial Graphene VL - 125 ER - TY - JOUR AU - Jain, Mitisha AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero AU - Aldahhak, Hazem ID - 40250 IS - 6 JF - Journal of Computational Chemistry KW - Computational Mathematics KW - General Chemistry SN - 0192-8651 TI - Adatom mediated adsorption of N‐heterocyclic carbenes on Cu(111) and Au(111) VL - 43 ER - TY - JOUR AB - 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. AU - Schmidt, Falko AU - Kozub, Agnieszka L. AU - Gerstmann, Uwe AU - Schmidt, Wolf Gero AU - Schindlmayr, Arno ID - 21946 JF - Crystals TI - Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response VL - 11 ER - TY - JOUR AU - Murzakhanov, F. F. AU - Yavkin, B. V. AU - Mamin, G. V. AU - Orlinskii, S. B. AU - von Bardeleben, H. J. AU - Biktagirov, Timur AU - Gerstmann, Uwe AU - Soltamov, V. A. ID - 29749 JF - Physical Review B SN - 2469-9950 TI - Hyperfine and nuclear quadrupole splitting of the NV− ground state in 4H-SiC VL - 103 ER - TY - JOUR AU - Aldahhak, Hazem AU - Hogan, Conor AU - Lindner, Susi AU - Appelfeller, Stephan AU - Eisele, Holger AU - Schmidt, Wolf Gero AU - Dähne, Mario AU - Gerstmann, Uwe AU - Franz, Martin ID - 22010 JF - Physical Review B SN - 2469-9950 TI - Electronic structure of the Si(111)3×3R30∘−B surface from theory and photoemission spectroscopy VL - 103 ER -