--- _id: '52723' abstract: - lang: eng text: Miller's rule is an empirical relation between the nonlinear and linear optical coefficients that applies to a large class of materials but has only been rigorously derived for the classical Lorentz model with a weak anharmonic perturbation. In this work, we extend the proof and present a detailed derivation of Miller's rule for an equivalent quantum-mechanical anharmonic oscillator. For this purpose, the classical concept of velocity-dependent damping inherent to the Lorentz model is replaced by an adiabatic switch-on of the external electric field, which allows a unified treatment of the classical and quantum-mechanical systems using identical potentials and fields. Although the dynamics of the resulting charge oscillations, and hence the induced polarizations, deviate due to the finite zero-point motion in the quantum-mechanical framework, we find that Miller's rule is nevertheless identical in both cases up to terms of first order in the anharmonicity. With a view to practical applications, especially in the context of ab initio calculations for the optical response where adiabatically switched-on fields are widely assumed, we demonstrate that a correct treatment of finite broadening parameters is essential to avoid spurious errors that may falsely suggest a violation of Miller's rule, and we illustrate this point by means of a numerical example. article_type: original author: - first_name: Maximilian Tim full_name: Meyer, Maximilian Tim last_name: Meyer - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: 'Meyer MT, Schindlmayr A. Derivation of Miller’s rule for the nonlinear optical susceptibility of a quantum anharmonic oscillator. Journal of Physics B: Atomic, Molecular and Optical Physics. doi:10.1088/1361-6455/ad369c' apa: 'Meyer, M. T., & Schindlmayr, A. (n.d.). Derivation of Miller’s rule for the nonlinear optical susceptibility of a quantum anharmonic oscillator. Journal of Physics B: Atomic, Molecular and Optical Physics. https://doi.org/10.1088/1361-6455/ad369c' bibtex: '@article{Meyer_Schindlmayr, title={Derivation of Miller’s rule for the nonlinear optical susceptibility of a quantum anharmonic oscillator}, DOI={10.1088/1361-6455/ad369c}, journal={Journal of Physics B: Atomic, Molecular and Optical Physics}, publisher={IOP Publishing}, author={Meyer, Maximilian Tim and Schindlmayr, Arno} }' chicago: 'Meyer, Maximilian Tim, and Arno Schindlmayr. “Derivation of Miller’s Rule for the Nonlinear Optical Susceptibility of a Quantum Anharmonic Oscillator.” Journal of Physics B: Atomic, Molecular and Optical Physics, n.d. https://doi.org/10.1088/1361-6455/ad369c.' ieee: 'M. T. Meyer and A. Schindlmayr, “Derivation of Miller’s rule for the nonlinear optical susceptibility of a quantum anharmonic oscillator,” Journal of Physics B: Atomic, Molecular and Optical Physics, doi: 10.1088/1361-6455/ad369c.' mla: 'Meyer, Maximilian Tim, and Arno Schindlmayr. “Derivation of Miller’s Rule for the Nonlinear Optical Susceptibility of a Quantum Anharmonic Oscillator.” Journal of Physics B: Atomic, Molecular and Optical Physics, IOP Publishing, doi:10.1088/1361-6455/ad369c.' short: 'M.T. Meyer, A. Schindlmayr, Journal of Physics B: Atomic, Molecular and Optical Physics (n.d.).' date_created: 2024-03-22T08:44:39Z date_updated: 2024-03-22T08:47:41Z department: - _id: '296' - _id: '230' - _id: '15' - _id: '170' - _id: '35' doi: 10.1088/1361-6455/ad369c language: - iso: eng publication: 'Journal of Physics B: Atomic, Molecular and Optical Physics' publication_identifier: eissn: - 1361-6455 issn: - 0953-4075 publication_status: accepted publisher: IOP Publishing quality_controlled: '1' status: public title: Derivation of Miller's rule for the nonlinear optical susceptibility of a quantum anharmonic oscillator type: journal_article user_id: '458' year: '2024' ... --- _id: '30288' abstract: - lang: eng text: 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. author: - first_name: Falko full_name: Schmidt, Falko id: '35251' last_name: Schmidt orcid: 0000-0002-5071-5528 - first_name: Agnieszka L. full_name: Kozub, Agnieszka L. id: '77566' last_name: Kozub orcid: https://orcid.org/0000-0001-6584-0201 - first_name: Uwe full_name: Gerstmann, Uwe id: '171' last_name: Gerstmann orcid: 0000-0002-4476-223X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: 'Schmidt F, Kozub AL, Gerstmann U, Schmidt WG, Schindlmayr A. Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response. In: Corradi G, Kovács L, eds. New Trends in Lithium Niobate: From Bulk to Nanocrystals. MDPI; 2022:231-248. doi:10.3390/books978-3-0365-3339-1' apa: 'Schmidt, F., Kozub, A. L., Gerstmann, U., Schmidt, W. G., & Schindlmayr, A. (2022). Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response. In G. Corradi & L. Kovács (Eds.), New Trends in Lithium Niobate: From Bulk to Nanocrystals (pp. 231–248). MDPI. https://doi.org/10.3390/books978-3-0365-3339-1' bibtex: '@inbook{Schmidt_Kozub_Gerstmann_Schmidt_Schindlmayr_2022, place={Basel}, title={Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response}, DOI={10.3390/books978-3-0365-3339-1}, booktitle={New Trends in Lithium Niobate: From Bulk to Nanocrystals}, publisher={MDPI}, author={Schmidt, Falko and Kozub, Agnieszka L. and Gerstmann, Uwe and Schmidt, Wolf Gero and Schindlmayr, Arno}, editor={Corradi, Gábor and Kovács, László}, year={2022}, pages={231–248} }' chicago: 'Schmidt, Falko, Agnieszka L. Kozub, Uwe Gerstmann, Wolf Gero Schmidt, and Arno Schindlmayr. “Electron Polarons in Lithium Niobate: Charge Localization, Lattice Deformation, and Optical Response.” In New Trends in Lithium Niobate: From Bulk to Nanocrystals, edited by Gábor Corradi and László Kovács, 231–48. Basel: MDPI, 2022. https://doi.org/10.3390/books978-3-0365-3339-1.' ieee: 'F. Schmidt, A. L. Kozub, U. Gerstmann, W. G. Schmidt, and A. Schindlmayr, “Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response,” in New Trends in Lithium Niobate: From Bulk to Nanocrystals, G. Corradi and L. Kovács, Eds. Basel: MDPI, 2022, pp. 231–248.' mla: 'Schmidt, Falko, et al. “Electron Polarons in Lithium Niobate: Charge Localization, Lattice Deformation, and Optical Response.” New Trends in Lithium Niobate: From Bulk to Nanocrystals, edited by Gábor Corradi and László Kovács, MDPI, 2022, pp. 231–48, doi:10.3390/books978-3-0365-3339-1.' short: 'F. Schmidt, A.L. Kozub, U. Gerstmann, W.G. Schmidt, A. Schindlmayr, in: G. Corradi, L. Kovács (Eds.), New Trends in Lithium Niobate: From Bulk to Nanocrystals, MDPI, Basel, 2022, pp. 231–248.' date_created: 2022-03-13T15:28:47Z date_updated: 2023-04-20T15:58:51Z ddc: - '530' department: - _id: '296' - _id: '230' - _id: '429' - _id: '295' - _id: '15' - _id: '170' - _id: '35' - _id: '790' doi: 10.3390/books978-3-0365-3339-1 editor: - first_name: Gábor full_name: Corradi, Gábor last_name: Corradi - first_name: László full_name: Kovács, László last_name: Kovács language: - iso: eng page: 231-248 place: Basel project: - _id: '53' name: 'TRR 142: TRR 142' - _id: '55' name: 'TRR 142 - B: TRR 142 - Project Area B' - _id: '69' name: 'TRR 142 - B4: TRR 142 - Subproject B4' - _id: '54' name: 'TRR 142 - A: TRR 142 - Project Area A' - _id: '166' name: 'TRR 142 - A11: TRR 142 - Subproject A11' - _id: '168' name: 'TRR 142 - B07: TRR 142 - Subproject B07' - _id: '52' name: 'PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing' publication: 'New Trends in Lithium Niobate: From Bulk to Nanocrystals' publication_identifier: eisbn: - 978-3-0365-3339-1 isbn: - 978-3-0365-3340-7 publication_status: published publisher: MDPI quality_controlled: '1' status: public title: 'Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response' type: book_chapter user_id: '16199' year: '2022' ... --- _id: '26627' abstract: - lang: eng text: 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. article_number: '015002' article_type: original author: - first_name: Sergej full_name: Neufeld, Sergej id: '23261' last_name: Neufeld - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 citation: ama: 'Neufeld S, Schindlmayr A, Schmidt WG. Quasiparticle energies and optical response of RbTiOPO4 and KTiOAsO4. Journal of Physics: Materials. 2022;5(1). doi:10.1088/2515-7639/ac3384' apa: 'Neufeld, S., Schindlmayr, A., & Schmidt, W. G. (2022). Quasiparticle energies and optical response of RbTiOPO4 and KTiOAsO4. Journal of Physics: Materials, 5(1), Article 015002. https://doi.org/10.1088/2515-7639/ac3384' bibtex: '@article{Neufeld_Schindlmayr_Schmidt_2022, title={Quasiparticle energies and optical response of RbTiOPO4 and KTiOAsO4}, volume={5}, DOI={10.1088/2515-7639/ac3384}, number={1015002}, journal={Journal of Physics: Materials}, publisher={IOP Publishing}, author={Neufeld, Sergej and Schindlmayr, Arno and Schmidt, Wolf Gero}, year={2022} }' chicago: 'Neufeld, Sergej, Arno Schindlmayr, and Wolf Gero Schmidt. “Quasiparticle Energies and Optical Response of RbTiOPO4 and KTiOAsO4.” Journal of Physics: Materials 5, no. 1 (2022). https://doi.org/10.1088/2515-7639/ac3384.' ieee: 'S. Neufeld, A. Schindlmayr, and W. G. Schmidt, “Quasiparticle energies and optical response of RbTiOPO4 and KTiOAsO4,” Journal of Physics: Materials, vol. 5, no. 1, Art. no. 015002, 2022, doi: 10.1088/2515-7639/ac3384.' mla: 'Neufeld, Sergej, et al. “Quasiparticle Energies and Optical Response of RbTiOPO4 and KTiOAsO4.” Journal of Physics: Materials, vol. 5, no. 1, 015002, IOP Publishing, 2022, doi:10.1088/2515-7639/ac3384.' short: 'S. Neufeld, A. Schindlmayr, W.G. Schmidt, Journal of Physics: Materials 5 (2022).' date_created: 2021-10-20T13:00:04Z date_updated: 2023-04-20T14:01:16Z ddc: - '530' department: - _id: '296' - _id: '295' - _id: '230' - _id: '429' - _id: '15' - _id: '170' - _id: '35' doi: 10.1088/2515-7639/ac3384 external_id: isi: - '000721060500001' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2021-11-22T17:57:00Z date_updated: 2021-11-22T17:57:00Z description: Creative Commons Attribution 4.0 International Public License (CC BY 4.0) file_id: '27705' file_name: Neufeld_2022_J._Phys._Mater._5_015002.pdf file_size: 2687065 relation: main_file title: Quasiparticle energies and optical response of RbTiOPO4 and KTiOAsO4 file_date_updated: 2021-11-22T17:57:00Z funded_apc: '1' has_accepted_license: '1' intvolume: ' 5' isi: '1' issue: '1' language: - iso: eng oa: '1' project: - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '52' name: 'PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing' - _id: '168' name: 'TRR 142 - B07: TRR 142 - Subproject B07' publication: 'Journal of Physics: Materials' publication_identifier: eissn: - 2515-7639 publication_status: published publisher: IOP Publishing quality_controlled: '1' status: public title: Quasiparticle energies and optical response of RbTiOPO4 and KTiOAsO4 type: journal_article user_id: '16199' volume: 5 year: '2022' ... --- _id: '29808' abstract: - lang: ger text: Dieses Format eignet sich, um zu prüfen, inwieweit Studierende Computersimulationen und eigene kleine Programme zur Lösung typischer Probleme ihres Fachs nutzen können. Wie bei Klausuren erfolgt die Bearbeitung in begrenzter Zeit und unter Aufsicht, wird aber am Computer durchgeführt und beinhaltet neben der Programmierung auch vor- und nachbereitende Aufgaben im Kontext der fachlichen Anwendung. author: - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: 'Schindlmayr A. Programmierung und Computersimulationen. In: Gerick J, Sommer A, Zimmermann G, eds. Kompetent Prüfungen gestalten: 60 Prüfungsformate für die Hochschullehre. 2nd ed. Waxmann; 2022:270-274. doi:10.36198/9783838558592' apa: 'Schindlmayr, A. (2022). Programmierung und Computersimulationen. In J. Gerick, A. Sommer, & G. Zimmermann (Eds.), Kompetent Prüfungen gestalten: 60 Prüfungsformate für die Hochschullehre (2nd ed., pp. 270–274). Waxmann. https://doi.org/10.36198/9783838558592' bibtex: '@inbook{Schindlmayr_2022, place={Münster}, edition={2}, title={Programmierung und Computersimulationen}, DOI={10.36198/9783838558592}, booktitle={Kompetent Prüfungen gestalten: 60 Prüfungsformate für die Hochschullehre}, publisher={Waxmann}, author={Schindlmayr, Arno}, editor={Gerick, Julia and Sommer, Angela and Zimmermann, Germo}, year={2022}, pages={270–274} }' chicago: 'Schindlmayr, Arno. “Programmierung und Computersimulationen.” In Kompetent Prüfungen gestalten: 60 Prüfungsformate für die Hochschullehre, edited by Julia Gerick, Angela Sommer, and Germo Zimmermann, 2nd ed., 270–74. Münster: Waxmann, 2022. https://doi.org/10.36198/9783838558592.' ieee: 'A. Schindlmayr, “Programmierung und Computersimulationen,” in Kompetent Prüfungen gestalten: 60 Prüfungsformate für die Hochschullehre, 2nd ed., J. Gerick, A. Sommer, and G. Zimmermann, Eds. Münster: Waxmann, 2022, pp. 270–274.' mla: 'Schindlmayr, Arno. “Programmierung und Computersimulationen.” Kompetent Prüfungen gestalten: 60 Prüfungsformate für die Hochschullehre, edited by Julia Gerick et al., 2nd ed., Waxmann, 2022, pp. 270–74, doi:10.36198/9783838558592.' short: 'A. Schindlmayr, in: J. Gerick, A. Sommer, G. Zimmermann (Eds.), Kompetent Prüfungen gestalten: 60 Prüfungsformate für die Hochschullehre, 2nd ed., Waxmann, Münster, 2022, pp. 270–274.' date_created: 2022-02-11T11:13:37Z date_updated: 2023-04-20T14:55:58Z department: - _id: '296' - _id: '170' - _id: '15' - _id: '35' doi: 10.36198/9783838558592 edition: '2' editor: - first_name: Julia full_name: Gerick, Julia last_name: Gerick - first_name: Angela full_name: Sommer, Angela last_name: Sommer - first_name: Germo full_name: Zimmermann, Germo last_name: Zimmermann language: - iso: ger page: 270-274 place: Münster publication: 'Kompetent Prüfungen gestalten: 60 Prüfungsformate für die Hochschullehre' publication_identifier: eisbn: - '9783838558592' isbn: - '9783825258597' publication_status: published publisher: Waxmann quality_controlled: '1' status: public title: Programmierung und Computersimulationen type: book_chapter user_id: '16199' year: '2022' ... --- _id: '44088' abstract: - lang: eng text: '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.' article_number: '1586' article_type: original author: - first_name: Falko full_name: Schmidt, Falko id: '35251' last_name: Schmidt orcid: 0000-0002-5071-5528 - first_name: Agnieszka L. full_name: Kozub, Agnieszka L. id: '77566' last_name: Kozub orcid: 0000-0001-6584-0201 - first_name: Uwe full_name: Gerstmann, Uwe id: '171' last_name: Gerstmann orcid: 0000-0002-4476-223X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: Schmidt F, Kozub AL, Gerstmann U, Schmidt WG, Schindlmayr A. A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate. Crystals. 2022;12(11). doi:10.3390/cryst12111586 apa: Schmidt, F., Kozub, A. L., Gerstmann, U., Schmidt, W. G., & Schindlmayr, A. (2022). A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate. Crystals, 12(11), Article 1586. https://doi.org/10.3390/cryst12111586 bibtex: '@article{Schmidt_Kozub_Gerstmann_Schmidt_Schindlmayr_2022, title={A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate}, volume={12}, DOI={10.3390/cryst12111586}, number={111586}, journal={Crystals}, publisher={MDPI AG}, author={Schmidt, Falko and Kozub, Agnieszka L. and Gerstmann, Uwe and Schmidt, Wolf Gero and Schindlmayr, Arno}, year={2022} }' chicago: Schmidt, Falko, Agnieszka L. Kozub, Uwe Gerstmann, Wolf Gero Schmidt, and Arno Schindlmayr. “A Density-Functional Theory Study of Hole and Defect-Bound Exciton Polarons in Lithium Niobate.” Crystals 12, no. 11 (2022). https://doi.org/10.3390/cryst12111586. ieee: 'F. Schmidt, A. L. Kozub, U. Gerstmann, W. G. Schmidt, and A. Schindlmayr, “A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate,” Crystals, vol. 12, no. 11, Art. no. 1586, 2022, doi: 10.3390/cryst12111586.' mla: Schmidt, Falko, et al. “A Density-Functional Theory Study of Hole and Defect-Bound Exciton Polarons in Lithium Niobate.” Crystals, vol. 12, no. 11, 1586, MDPI AG, 2022, doi:10.3390/cryst12111586. short: F. Schmidt, A.L. Kozub, U. Gerstmann, W.G. Schmidt, A. Schindlmayr, Crystals 12 (2022). date_created: 2023-04-20T13:52:44Z date_updated: 2024-03-22T08:47:08Z ddc: - '530' department: - _id: '15' - _id: '296' - _id: '170' - _id: '295' - _id: '35' - _id: '230' - _id: '429' doi: 10.3390/cryst12111586 external_id: isi: - '000895837200001' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2023-06-11T23:59:27Z date_updated: 2023-06-12T00:22:51Z description: Creative Commons Attribution 4.0 International Public License (CC BY 4.0) file_id: '45570' file_name: crystals-12-01586-v2.pdf file_size: 1762554 relation: main_file title: A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate file_date_updated: 2023-06-12T00:22:51Z has_accepted_license: '1' intvolume: ' 12' isi: '1' issue: '11' language: - iso: eng oa: '1' project: - _id: '53' grant_number: '231447078' name: 'TRR 142: TRR 142' - _id: '54' name: 'TRR 142 - A: TRR 142 - Project Area A' - _id: '55' name: 'TRR 142 - B: TRR 142 - Project Area B' - _id: '69' grant_number: '231447078' name: 'TRR 142 - B04: TRR 142 - Subproject B04' - _id: '168' grant_number: '231447078' name: 'TRR 142 - B07: TRR 142 - Subproject B07' - _id: '166' name: 'TRR 142 - A11: TRR 142 - Subproject A11' - _id: '52' name: 'PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing' publication: Crystals publication_identifier: eissn: - 2073-4352 publication_status: published publisher: MDPI AG quality_controlled: '1' status: public title: A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate type: journal_article user_id: '458' volume: 12 year: '2022' ... --- _id: '21946' abstract: - lang: eng text: 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. article_type: original author: - first_name: Falko full_name: Schmidt, Falko id: '35251' last_name: Schmidt orcid: 0000-0002-5071-5528 - first_name: Agnieszka L. full_name: Kozub, Agnieszka L. id: '77566' last_name: Kozub orcid: https://orcid.org/0000-0001-6584-0201 - first_name: Uwe full_name: Gerstmann, Uwe id: '171' last_name: Gerstmann orcid: 0000-0002-4476-223X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: 'Schmidt F, Kozub AL, Gerstmann U, Schmidt WG, Schindlmayr A. Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response. Crystals. 2021;11:542. doi:10.3390/cryst11050542' apa: 'Schmidt, F., Kozub, A. L., Gerstmann, U., Schmidt, W. G., & Schindlmayr, A. (2021). Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response. Crystals, 11, 542. https://doi.org/10.3390/cryst11050542' bibtex: '@article{Schmidt_Kozub_Gerstmann_Schmidt_Schindlmayr_2021, title={Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response}, volume={11}, DOI={10.3390/cryst11050542}, journal={Crystals}, publisher={MDPI}, author={Schmidt, Falko and Kozub, Agnieszka L. and Gerstmann, Uwe and Schmidt, Wolf Gero and Schindlmayr, Arno}, year={2021}, pages={542} }' chicago: 'Schmidt, Falko, Agnieszka L. Kozub, Uwe Gerstmann, Wolf Gero Schmidt, and Arno Schindlmayr. “Electron Polarons in Lithium Niobate: Charge Localization, Lattice Deformation, and Optical Response.” Crystals 11 (2021): 542. https://doi.org/10.3390/cryst11050542.' ieee: 'F. Schmidt, A. L. Kozub, U. Gerstmann, W. G. Schmidt, and A. Schindlmayr, “Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response,” Crystals, vol. 11, p. 542, 2021, doi: 10.3390/cryst11050542.' mla: 'Schmidt, Falko, et al. “Electron Polarons in Lithium Niobate: Charge Localization, Lattice Deformation, and Optical Response.” Crystals, vol. 11, MDPI, 2021, p. 542, doi:10.3390/cryst11050542.' short: F. Schmidt, A.L. Kozub, U. Gerstmann, W.G. Schmidt, A. Schindlmayr, Crystals 11 (2021) 542. date_created: 2021-05-03T09:36:13Z date_updated: 2023-04-21T11:20:15Z ddc: - '530' department: - _id: '296' - _id: '230' - _id: '429' - _id: '295' - _id: '15' - _id: '170' - _id: '35' - _id: '790' doi: 10.3390/cryst11050542 external_id: isi: - '000653822700001' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2021-05-13T16:47:11Z date_updated: 2021-05-13T16:51:41Z description: Creative Commons Attribution 4.0 International Public License (CC BY 4.0) file_id: '22163' file_name: crystals-11-00542.pdf file_size: 3042827 relation: main_file title: 'Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response' file_date_updated: 2021-05-13T16:51:41Z funded_apc: '1' has_accepted_license: '1' intvolume: ' 11' isi: '1' language: - iso: eng oa: '1' page: '542' project: - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '52' name: 'PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing' publication: Crystals publication_identifier: eissn: - 2073-4352 publication_status: published publisher: MDPI quality_controlled: '1' status: public title: 'Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response' type: journal_article user_id: '171' volume: 11 year: '2021' ... --- _id: '22960' abstract: - lang: eng text: We perform a theoretical analysis of the structural and electronic properties of sodium potassium niobate K1-xNaxNbO3 in the orthorhombic room-temperature phase, based on density-functional theory in combination with the supercell approach. Our results for x=0 and x=0.5 are in very good agreement with experimental measurements and establish that the lattice parameters decrease linearly with increasing Na contents, disproving earlier theoretical studies based on the virtual-crystal approximation that claimed a highly nonlinear behavior with a significant structural distortion and volume reduction in K0.5Na0.5NbO3 compared to both end members of the solid solution. Furthermore, we find that the electronic band gap varies very little between x=0 and x=0.5, reflecting the small changes in the lattice parameters. article_number: '169' article_type: original author: - first_name: Nithin full_name: Bidaraguppe Ramesh, Nithin id: '70064' last_name: Bidaraguppe Ramesh - first_name: Falko full_name: Schmidt, Falko id: '35251' last_name: Schmidt orcid: 0000-0002-5071-5528 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: Bidaraguppe Ramesh N, Schmidt F, Schindlmayr A. Lattice parameters and electronic band gap of orthorhombic potassium sodium niobate K0.5Na0.5NbO3 from density-functional theory. The European Physical Journal B. 2021;94(8). doi:10.1140/epjb/s10051-021-00179-8 apa: Bidaraguppe Ramesh, N., Schmidt, F., & Schindlmayr, A. (2021). Lattice parameters and electronic band gap of orthorhombic potassium sodium niobate K0.5Na0.5NbO3 from density-functional theory. The European Physical Journal B, 94(8), Article 169. https://doi.org/10.1140/epjb/s10051-021-00179-8 bibtex: '@article{Bidaraguppe Ramesh_Schmidt_Schindlmayr_2021, title={Lattice parameters and electronic band gap of orthorhombic potassium sodium niobate K0.5Na0.5NbO3 from density-functional theory}, volume={94}, DOI={10.1140/epjb/s10051-021-00179-8}, number={8169}, journal={The European Physical Journal B}, publisher={EDP Sciences, Società Italiana di Fisica and Springer}, author={Bidaraguppe Ramesh, Nithin and Schmidt, Falko and Schindlmayr, Arno}, year={2021} }' chicago: Bidaraguppe Ramesh, Nithin, Falko Schmidt, and Arno Schindlmayr. “Lattice Parameters and Electronic Band Gap of Orthorhombic Potassium Sodium Niobate K0.5Na0.5NbO3 from Density-Functional Theory.” The European Physical Journal B 94, no. 8 (2021). https://doi.org/10.1140/epjb/s10051-021-00179-8. ieee: 'N. Bidaraguppe Ramesh, F. Schmidt, and A. Schindlmayr, “Lattice parameters and electronic band gap of orthorhombic potassium sodium niobate K0.5Na0.5NbO3 from density-functional theory,” The European Physical Journal B, vol. 94, no. 8, Art. no. 169, 2021, doi: 10.1140/epjb/s10051-021-00179-8.' mla: Bidaraguppe Ramesh, Nithin, et al. “Lattice Parameters and Electronic Band Gap of Orthorhombic Potassium Sodium Niobate K0.5Na0.5NbO3 from Density-Functional Theory.” The European Physical Journal B, vol. 94, no. 8, 169, EDP Sciences, Società Italiana di Fisica and Springer, 2021, doi:10.1140/epjb/s10051-021-00179-8. short: N. Bidaraguppe Ramesh, F. Schmidt, A. Schindlmayr, The European Physical Journal B 94 (2021). date_created: 2021-08-08T21:21:42Z date_updated: 2023-04-20T14:56:25Z ddc: - '530' department: - _id: '296' - _id: '230' - _id: '429' - _id: '15' - _id: '170' - _id: '35' doi: 10.1140/epjb/s10051-021-00179-8 external_id: isi: - '000687163200002' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2021-09-02T08:05:06Z date_updated: 2021-09-02T08:05:06Z description: Creative Commons Attribution 4.0 International Public License (CC BY 4.0) file_id: '23679' file_name: BidaraguppeRamesh2021_Article_LatticeParametersAndElectronic.pdf file_size: 850389 relation: main_file title: Lattice parameters and electronic bandgap of orthorhombic potassium sodium niobate K0.5Na0.5NbO3 from density-functional theory file_date_updated: 2021-09-02T08:05:06Z has_accepted_license: '1' intvolume: ' 94' isi: '1' issue: '8' language: - iso: eng oa: '1' project: - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 publication: The European Physical Journal B publication_identifier: eissn: - 1434-6036 issn: - 1434-6028 publication_status: published publisher: EDP Sciences, Società Italiana di Fisica and Springer quality_controlled: '1' status: public title: Lattice parameters and electronic band gap of orthorhombic potassium sodium niobate K0.5Na0.5NbO3 from density-functional theory type: journal_article user_id: '16199' volume: 94 year: '2021' ... --- _id: '22761' article_number: '039901' author: - first_name: Christoph full_name: Friedrich, Christoph last_name: Friedrich - first_name: Stefan full_name: Blügel, Stefan last_name: Blügel - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: 'Friedrich C, Blügel S, Schindlmayr A. Erratum: Efficient implementation of the GW approximation within the all-electron FLAPW method [Phys. Rev. B 81, 125102 (2010)]. Physical Review B. 2021;104(3). doi:10.1103/PhysRevB.104.039901' apa: 'Friedrich, C., Blügel, S., & Schindlmayr, A. (2021). Erratum: Efficient implementation of the GW approximation within the all-electron FLAPW method [Phys. Rev. B 81, 125102 (2010)]. Physical Review B, 104(3), Article 039901. https://doi.org/10.1103/PhysRevB.104.039901' bibtex: '@article{Friedrich_Blügel_Schindlmayr_2021, title={Erratum: Efficient implementation of the GW approximation within the all-electron FLAPW method [Phys. Rev. B 81, 125102 (2010)]}, volume={104}, DOI={10.1103/PhysRevB.104.039901}, number={3039901}, journal={Physical Review B}, publisher={American Physical Society}, author={Friedrich, Christoph and Blügel, Stefan and Schindlmayr, Arno}, year={2021} }' chicago: 'Friedrich, Christoph, Stefan Blügel, and Arno Schindlmayr. “Erratum: Efficient Implementation of the GW Approximation within the All-Electron FLAPW Method [Phys. Rev. B 81, 125102 (2010)].” Physical Review B 104, no. 3 (2021). https://doi.org/10.1103/PhysRevB.104.039901.' ieee: 'C. Friedrich, S. Blügel, and A. Schindlmayr, “Erratum: Efficient implementation of the GW approximation within the all-electron FLAPW method [Phys. Rev. B 81, 125102 (2010)],” Physical Review B, vol. 104, no. 3, Art. no. 039901, 2021, doi: 10.1103/PhysRevB.104.039901.' mla: 'Friedrich, Christoph, et al. “Erratum: Efficient Implementation of the GW Approximation within the All-Electron FLAPW Method [Phys. Rev. B 81, 125102 (2010)].” Physical Review B, vol. 104, no. 3, 039901, American Physical Society, 2021, doi:10.1103/PhysRevB.104.039901.' short: C. Friedrich, S. Blügel, A. Schindlmayr, Physical Review B 104 (2021). date_created: 2021-07-15T19:59:00Z date_updated: 2023-04-20T14:57:09Z ddc: - '530' department: - _id: '296' - _id: '15' - _id: '170' doi: 10.1103/PhysRevB.104.039901 external_id: isi: - '000671587300006' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2021-07-15T20:16:55Z date_updated: 2021-07-15T20:16:55Z description: © 2021 American Physical Society file_id: '22763' file_name: PhysRevB.104.039901.pdf file_size: 180926 relation: main_file title: 'Erratum: Efficient implementation of the GW approximation within the all-electron FLAPW method [Phys. Rev. B 81, 125102 (2010)]' file_date_updated: 2021-07-15T20:16:55Z has_accepted_license: '1' intvolume: ' 104' isi: '1' issue: '3' language: - iso: eng oa: '1' publication: Physical Review B publication_identifier: eissn: - 2469-9969 issn: - 2469-9950 publication_status: published publisher: American Physical Society quality_controlled: '1' related_material: record: - id: '18558' relation: other status: public status: public title: 'Erratum: Efficient implementation of the GW approximation within the all-electron FLAPW method [Phys. Rev. B 81, 125102 (2010)]' type: journal_article user_id: '16199' volume: 104 year: '2021' ... --- _id: '23418' abstract: - lang: eng text: 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. article_type: original author: - first_name: Agnieszka L. full_name: Kozub, Agnieszka L. id: '77566' last_name: Kozub orcid: https://orcid.org/0000-0001-6584-0201 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Uwe full_name: Gerstmann, Uwe id: '171' last_name: Gerstmann orcid: 0000-0002-4476-223X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 citation: ama: Kozub AL, Schindlmayr A, Gerstmann U, Schmidt WG. Polaronic enhancement of second-harmonic generation in lithium niobate. Physical Review B. 2021;104:174110. doi:10.1103/PhysRevB.104.174110 apa: Kozub, A. L., Schindlmayr, A., Gerstmann, U., & Schmidt, W. G. (2021). Polaronic enhancement of second-harmonic generation in lithium niobate. Physical Review B, 104, 174110. https://doi.org/10.1103/PhysRevB.104.174110 bibtex: '@article{Kozub_Schindlmayr_Gerstmann_Schmidt_2021, title={Polaronic enhancement of second-harmonic generation in lithium niobate}, volume={104}, DOI={10.1103/PhysRevB.104.174110}, journal={Physical Review B}, publisher={American Physical Society}, author={Kozub, Agnieszka L. and Schindlmayr, Arno and Gerstmann, Uwe and Schmidt, Wolf Gero}, year={2021}, pages={174110} }' chicago: 'Kozub, Agnieszka L., Arno Schindlmayr, Uwe Gerstmann, and Wolf Gero Schmidt. “Polaronic Enhancement of Second-Harmonic Generation in Lithium Niobate.” Physical Review B 104 (2021): 174110. https://doi.org/10.1103/PhysRevB.104.174110.' ieee: 'A. L. Kozub, A. Schindlmayr, U. Gerstmann, and W. G. Schmidt, “Polaronic enhancement of second-harmonic generation in lithium niobate,” Physical Review B, vol. 104, p. 174110, 2021, doi: 10.1103/PhysRevB.104.174110.' mla: Kozub, Agnieszka L., et al. “Polaronic Enhancement of Second-Harmonic Generation in Lithium Niobate.” Physical Review B, vol. 104, American Physical Society, 2021, p. 174110, doi:10.1103/PhysRevB.104.174110. short: A.L. Kozub, A. Schindlmayr, U. Gerstmann, W.G. Schmidt, Physical Review B 104 (2021) 174110. date_created: 2021-08-16T19:09:46Z date_updated: 2023-04-21T11:15:30Z ddc: - '530' department: - _id: '296' - _id: '230' - _id: '429' - _id: '295' - _id: '15' - _id: '170' - _id: '790' doi: 10.1103/PhysRevB.104.174110 external_id: arxiv: - '2106.01145' isi: - '000720931400007' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2021-11-18T20:49:19Z date_updated: 2021-11-18T20:49:19Z description: © 2021 American Physical Society file_id: '27577' file_name: PhysRevB.104.174110.pdf file_size: 804012 relation: main_file title: Polaronic enhancement of second-harmonic generation in lithium niobate file_date_updated: 2021-11-18T20:49:19Z has_accepted_license: '1' intvolume: ' 104' isi: '1' language: - iso: eng oa: '1' page: '174110' project: - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 - _id: '52' name: 'PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing' publication: Physical Review B publication_identifier: eissn: - 2469-9969 issn: - 2469-9950 publication_status: published publisher: American Physical Society quality_controlled: '1' status: public title: Polaronic enhancement of second-harmonic generation in lithium niobate type: journal_article user_id: '171' volume: 104 year: '2021' ... --- _id: '19190' abstract: - lang: eng text: "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 \r\npolarons 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 \r\nNb_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." article_number: '043002' article_type: original author: - first_name: Falko full_name: Schmidt, Falko id: '35251' last_name: Schmidt orcid: 0000-0002-5071-5528 - first_name: Agnieszka L. full_name: Kozub, Agnieszka L. id: '77566' last_name: Kozub orcid: https://orcid.org/0000-0001-6584-0201 - first_name: Timur full_name: Biktagirov, Timur id: '65612' last_name: Biktagirov - first_name: Christof full_name: Eigner, Christof id: '13244' last_name: Eigner orcid: https://orcid.org/0000-0002-5693-3083 - first_name: Christine full_name: Silberhorn, Christine id: '26263' last_name: Silberhorn - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Uwe full_name: Gerstmann, Uwe id: '171' last_name: Gerstmann orcid: 0000-0002-4476-223X citation: ama: 'Schmidt F, Kozub AL, Biktagirov T, et al. Free and defect-bound (bi)polarons in LiNbO3: Atomic structure and spectroscopic signatures from ab initio calculations. Physical Review Research. 2020;2(4). doi:10.1103/PhysRevResearch.2.043002' apa: 'Schmidt, F., Kozub, A. L., Biktagirov, T., Eigner, C., Silberhorn, C., Schindlmayr, A., Schmidt, W. G., & Gerstmann, U. (2020). Free and defect-bound (bi)polarons in LiNbO3: Atomic structure and spectroscopic signatures from ab initio calculations. Physical Review Research, 2(4), Article 043002. https://doi.org/10.1103/PhysRevResearch.2.043002' bibtex: '@article{Schmidt_Kozub_Biktagirov_Eigner_Silberhorn_Schindlmayr_Schmidt_Gerstmann_2020, title={Free and defect-bound (bi)polarons in LiNbO3: Atomic structure and spectroscopic signatures from ab initio calculations}, volume={2}, DOI={10.1103/PhysRevResearch.2.043002}, number={4043002}, journal={Physical Review Research}, publisher={American Physical Society}, author={Schmidt, Falko and Kozub, Agnieszka L. and Biktagirov, Timur and Eigner, Christof and Silberhorn, Christine and Schindlmayr, Arno and Schmidt, Wolf Gero and Gerstmann, Uwe}, year={2020} }' chicago: 'Schmidt, Falko, Agnieszka L. Kozub, Timur Biktagirov, Christof Eigner, Christine Silberhorn, Arno Schindlmayr, Wolf Gero Schmidt, and Uwe Gerstmann. “Free and Defect-Bound (Bi)Polarons in LiNbO3: Atomic Structure and Spectroscopic Signatures from Ab Initio Calculations.” Physical Review Research 2, no. 4 (2020). https://doi.org/10.1103/PhysRevResearch.2.043002.' ieee: 'F. Schmidt et al., “Free and defect-bound (bi)polarons in LiNbO3: Atomic structure and spectroscopic signatures from ab initio calculations,” Physical Review Research, vol. 2, no. 4, Art. no. 043002, 2020, doi: 10.1103/PhysRevResearch.2.043002.' mla: 'Schmidt, Falko, et al. “Free and Defect-Bound (Bi)Polarons in LiNbO3: Atomic Structure and Spectroscopic Signatures from Ab Initio Calculations.” Physical Review Research, vol. 2, no. 4, 043002, American Physical Society, 2020, doi:10.1103/PhysRevResearch.2.043002.' short: F. Schmidt, A.L. Kozub, T. Biktagirov, C. Eigner, C. Silberhorn, A. Schindlmayr, W.G. Schmidt, U. Gerstmann, Physical Review Research 2 (2020). date_created: 2020-09-09T09:35:21Z date_updated: 2023-04-20T16:06:21Z ddc: - '530' department: - _id: '296' - _id: '230' - _id: '429' - _id: '295' - _id: '288' - _id: '15' - _id: '170' - _id: '35' - _id: '790' doi: 10.1103/PhysRevResearch.2.043002 external_id: isi: - '000604206300002' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-10-02T07:27:38Z date_updated: 2020-10-02T07:37:24Z description: Creative Commons Attribution 4.0 International Public License (CC BY 4.0) file_id: '19843' file_name: PhysRevResearch.2.043002.pdf file_size: 1955183 relation: main_file title: 'Free and defect-bound (bi)polarons in LiNbO3: Atomic structure and spectroscopic signatures from ab initio calculations' file_date_updated: 2020-10-02T07:37:24Z has_accepted_license: '1' intvolume: ' 2' isi: '1' issue: '4' language: - iso: eng oa: '1' project: - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '52' name: 'PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing' publication: Physical Review Research publication_identifier: eissn: - 2643-1564 publication_status: published publisher: American Physical Society quality_controlled: '1' status: public title: 'Free and defect-bound (bi)polarons in LiNbO3: Atomic structure and spectroscopic signatures from ab initio calculations' type: journal_article user_id: '16199' volume: 2 year: '2020' ... --- _id: '10014' abstract: - lang: eng text: 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. article_number: '054401' article_type: original author: - first_name: Falko full_name: Schmidt, Falko id: '35251' last_name: Schmidt orcid: 0000-0002-5071-5528 - first_name: Arthur full_name: Riefer, Arthur last_name: Riefer - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Mirco full_name: Imlau, Mirco last_name: Imlau - first_name: Florian full_name: Dobener, Florian last_name: Dobener - first_name: Nils full_name: Mengel, Nils last_name: Mengel - first_name: Sangam full_name: Chatterjee, Sangam last_name: Chatterjee - first_name: Simone full_name: Sanna, Simone last_name: Sanna citation: ama: Schmidt F, Riefer A, Schmidt WG, et al. Quasiparticle and excitonic effects in the optical response of KNbO3. Physical Review Materials. 2019;3(5). doi:10.1103/PhysRevMaterials.3.054401 apa: Schmidt, F., Riefer, A., Schmidt, W. G., Schindlmayr, A., Imlau, M., Dobener, F., Mengel, N., Chatterjee, S., & Sanna, S. (2019). Quasiparticle and excitonic effects in the optical response of KNbO3. Physical Review Materials, 3(5), Article 054401. https://doi.org/10.1103/PhysRevMaterials.3.054401 bibtex: '@article{Schmidt_Riefer_Schmidt_Schindlmayr_Imlau_Dobener_Mengel_Chatterjee_Sanna_2019, title={Quasiparticle and excitonic effects in the optical response of KNbO3}, volume={3}, DOI={10.1103/PhysRevMaterials.3.054401}, number={5054401}, journal={Physical Review Materials}, publisher={American Physical Society}, author={Schmidt, Falko and Riefer, Arthur and Schmidt, Wolf Gero and Schindlmayr, Arno and Imlau, Mirco and Dobener, Florian and Mengel, Nils and Chatterjee, Sangam and Sanna, Simone}, year={2019} }' chicago: Schmidt, Falko, Arthur Riefer, Wolf Gero Schmidt, Arno Schindlmayr, Mirco Imlau, Florian Dobener, Nils Mengel, Sangam Chatterjee, and Simone Sanna. “Quasiparticle and Excitonic Effects in the Optical Response of KNbO3.” Physical Review Materials 3, no. 5 (2019). https://doi.org/10.1103/PhysRevMaterials.3.054401. ieee: 'F. Schmidt et al., “Quasiparticle and excitonic effects in the optical response of KNbO3,” Physical Review Materials, vol. 3, no. 5, Art. no. 054401, 2019, doi: 10.1103/PhysRevMaterials.3.054401.' mla: Schmidt, Falko, et al. “Quasiparticle and Excitonic Effects in the Optical Response of KNbO3.” Physical Review Materials, vol. 3, no. 5, 054401, American Physical Society, 2019, doi:10.1103/PhysRevMaterials.3.054401. short: F. Schmidt, A. Riefer, W.G. Schmidt, A. Schindlmayr, M. Imlau, F. Dobener, N. Mengel, S. Chatterjee, S. Sanna, Physical Review Materials 3 (2019). date_created: 2019-05-29T06:55:29Z date_updated: 2023-04-20T14:20:33Z ddc: - '530' department: - _id: '295' - _id: '296' - _id: '230' - _id: '429' - _id: '170' - _id: '35' doi: 10.1103/PhysRevMaterials.3.054401 external_id: isi: - '000467044000003' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-08-27T19:05:54Z date_updated: 2020-08-30T14:34:33Z description: © 2019 American Physical Society file_id: '18465' file_name: PhysRevMaterials.3.054401.pdf file_size: 1949504 relation: main_file title: Quasiparticle and excitonic effects in the optical response of KNbO3 file_date_updated: 2020-08-30T14:34:33Z has_accepted_license: '1' intvolume: ' 3' isi: '1' issue: '5' language: - iso: eng oa: '1' project: - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 - _id: '52' name: 'PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing' publication: Physical Review Materials publication_identifier: eissn: - 2475-9953 publication_status: published publisher: American Physical Society quality_controlled: '1' status: public title: Quasiparticle and excitonic effects in the optical response of KNbO3 type: journal_article user_id: '16199' volume: 3 year: '2019' ... --- _id: '13365' abstract: - lang: eng text: '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.' article_type: original author: - first_name: Sergej full_name: Neufeld, Sergej id: '23261' last_name: Neufeld - first_name: Adriana full_name: Bocchini, Adriana id: '58349' last_name: Bocchini orcid: https://orcid.org/0000-0002-2134-3075 - first_name: Uwe full_name: Gerstmann, Uwe id: '171' last_name: Gerstmann orcid: 0000-0002-4476-223X - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 citation: ama: 'Neufeld S, Bocchini A, Gerstmann U, Schindlmayr A, Schmidt WG. Potassium titanyl phosphate (KTP) quasiparticle energies and optical response. Journal of Physics: Materials. 2019;2:045003. doi:10.1088/2515-7639/ab29ba' apa: 'Neufeld, S., Bocchini, A., Gerstmann, U., Schindlmayr, A., & Schmidt, W. G. (2019). Potassium titanyl phosphate (KTP) quasiparticle energies and optical response. Journal of Physics: Materials, 2, 045003. https://doi.org/10.1088/2515-7639/ab29ba' bibtex: '@article{Neufeld_Bocchini_Gerstmann_Schindlmayr_Schmidt_2019, title={Potassium titanyl phosphate (KTP) quasiparticle energies and optical response}, volume={2}, DOI={10.1088/2515-7639/ab29ba}, journal={Journal of Physics: Materials}, publisher={IOP Publishing}, author={Neufeld, Sergej and Bocchini, Adriana and Gerstmann, Uwe and Schindlmayr, Arno and Schmidt, Wolf Gero}, year={2019}, pages={045003} }' chicago: 'Neufeld, Sergej, Adriana Bocchini, Uwe Gerstmann, Arno Schindlmayr, and Wolf Gero Schmidt. “Potassium Titanyl Phosphate (KTP) Quasiparticle Energies and Optical Response.” Journal of Physics: Materials 2 (2019): 045003. https://doi.org/10.1088/2515-7639/ab29ba.' ieee: 'S. Neufeld, A. Bocchini, U. Gerstmann, A. Schindlmayr, and W. G. Schmidt, “Potassium titanyl phosphate (KTP) quasiparticle energies and optical response,” Journal of Physics: Materials, vol. 2, p. 045003, 2019, doi: 10.1088/2515-7639/ab29ba.' mla: 'Neufeld, Sergej, et al. “Potassium Titanyl Phosphate (KTP) Quasiparticle Energies and Optical Response.” Journal of Physics: Materials, vol. 2, IOP Publishing, 2019, p. 045003, doi:10.1088/2515-7639/ab29ba.' short: 'S. Neufeld, A. Bocchini, U. Gerstmann, A. Schindlmayr, W.G. Schmidt, Journal of Physics: Materials 2 (2019) 045003.' date_created: 2019-09-19T14:34:16Z date_updated: 2023-04-21T11:36:12Z ddc: - '530' department: - _id: '296' - _id: '295' - _id: '230' - _id: '429' - _id: '170' - _id: '35' doi: 10.1088/2515-7639/ab29ba external_id: isi: - '000560410300003' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-08-28T09:07:18Z date_updated: 2020-08-30T14:29:27Z description: Creative Commons Attribution 3.0 Unported Public License (CC BY 3.0) file_id: '18535' file_name: Neufeld_2019_J._Phys._Mater._2_045003.pdf file_size: 1481174 relation: main_file title: Potassium titanyl phosphate (KTP) quasiparticle energies and optical response file_date_updated: 2020-08-30T14:29:27Z has_accepted_license: '1' intvolume: ' 2' isi: '1' language: - iso: eng license: https://creativecommons.org/licenses/by/3.0/ oa: '1' page: '045003' project: - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 - _id: '52' name: 'PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing' publication: 'Journal of Physics: Materials' publication_identifier: eissn: - 2515-7639 publication_status: published publisher: IOP Publishing quality_controlled: '1' status: public title: Potassium titanyl phosphate (KTP) quasiparticle energies and optical response type: journal_article user_id: '171' volume: 2 year: '2019' ... --- _id: '18466' abstract: - lang: eng text: The transverse dynamic spin susceptibility is a correlation function that yields exact information about spin excitations in systems with a collinear magnetic ground state, including collective spin-wave modes. In an ab initio context, it may be calculated within many-body perturbation theory or time-dependent density-functional theory, but the quantitative accuracy is currently limited by the available functionals for exchange and correlation in dynamically evolving systems. To circumvent this limitation, the spin susceptibility is here alternatively formulated as the solution of an initial-value problem. In this way, the challenge of accurately describing exchange and correlation in many-electron systems is shifted to the stationary initial state, which is much better understood. The proposed scheme further requires the choice of an auxiliary basis set, which determines the speed of convergence but always allows systematic convergence in practical implementations. article_number: '3732892' article_type: original author: - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: Schindlmayr A. Exact formulation of the transverse dynamic spin susceptibility as an initial-value problem. Advances in Mathematical Physics. 2018;2018. doi:10.1155/2018/3732892 apa: Schindlmayr, A. (2018). Exact formulation of the transverse dynamic spin susceptibility as an initial-value problem. Advances in Mathematical Physics, 2018. https://doi.org/10.1155/2018/3732892 bibtex: '@article{Schindlmayr_2018, title={Exact formulation of the transverse dynamic spin susceptibility as an initial-value problem}, volume={2018}, DOI={10.1155/2018/3732892}, number={3732892}, journal={Advances in Mathematical Physics}, publisher={Hindawi}, author={Schindlmayr, Arno}, year={2018} }' chicago: Schindlmayr, Arno. “Exact Formulation of the Transverse Dynamic Spin Susceptibility as an Initial-Value Problem.” Advances in Mathematical Physics 2018 (2018). https://doi.org/10.1155/2018/3732892. ieee: A. Schindlmayr, “Exact formulation of the transverse dynamic spin susceptibility as an initial-value problem,” Advances in Mathematical Physics, vol. 2018, 2018. mla: Schindlmayr, Arno. “Exact Formulation of the Transverse Dynamic Spin Susceptibility as an Initial-Value Problem.” Advances in Mathematical Physics, vol. 2018, 3732892, Hindawi, 2018, doi:10.1155/2018/3732892. short: A. Schindlmayr, Advances in Mathematical Physics 2018 (2018). date_created: 2020-08-27T19:18:34Z date_updated: 2022-01-06T06:53:33Z ddc: - '530' department: - _id: '296' doi: 10.1155/2018/3732892 external_id: isi: - '000422773000001' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-08-28T09:18:25Z date_updated: 2020-08-30T14:31:38Z description: Creative Commons Attribution 4.0 International Public License (CC BY 4.0) file_id: '18537' file_name: 3732892.pdf file_size: 294410 relation: main_file title: Exact formulation of the transverse dynamic spin susceptibility as an initial-value problem file_date_updated: 2020-08-30T14:31:38Z has_accepted_license: '1' intvolume: ' 2018' isi: '1' language: - iso: eng oa: '1' publication: Advances in Mathematical Physics publication_identifier: eissn: - 1687-9139 issn: - 1687-9120 publication_status: published publisher: Hindawi quality_controlled: '1' status: public title: Exact formulation of the transverse dynamic spin susceptibility as an initial-value problem type: journal_article user_id: '458' volume: 2018 year: '2018' ... --- _id: '13410' article_number: '019902' author: - first_name: Michael full_name: Friedrich, Michael last_name: Friedrich - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Simone full_name: Sanna, Simone last_name: Sanna citation: ama: 'Friedrich M, Schmidt WG, Schindlmayr A, Sanna S. Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)]. Physical Review Materials. 2018;2(1). doi:10.1103/PhysRevMaterials.2.019902' apa: 'Friedrich, M., Schmidt, W. G., Schindlmayr, A., & Sanna, S. (2018). Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)]. Physical Review Materials, 2(1). https://doi.org/10.1103/PhysRevMaterials.2.019902' bibtex: '@article{Friedrich_Schmidt_Schindlmayr_Sanna_2018, title={Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)]}, volume={2}, DOI={10.1103/PhysRevMaterials.2.019902}, number={1019902}, journal={Physical Review Materials}, publisher={American Physical Society}, author={Friedrich, Michael and Schmidt, Wolf Gero and Schindlmayr, Arno and Sanna, Simone}, year={2018} }' chicago: 'Friedrich, Michael, Wolf Gero Schmidt, Arno Schindlmayr, and Simone Sanna. “Erratum: Optical Properties of Titanium-Doped Lithium Niobate from Time-Dependent Density-Functional Theory [Phys. Rev. Materials 1, 034401 (2017)].” Physical Review Materials 2, no. 1 (2018). https://doi.org/10.1103/PhysRevMaterials.2.019902.' ieee: 'M. Friedrich, W. G. Schmidt, A. Schindlmayr, and S. Sanna, “Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)],” Physical Review Materials, vol. 2, no. 1, 2018.' mla: 'Friedrich, Michael, et al. “Erratum: Optical Properties of Titanium-Doped Lithium Niobate from Time-Dependent Density-Functional Theory [Phys. Rev. Materials 1, 034401 (2017)].” Physical Review Materials, vol. 2, no. 1, 019902, American Physical Society, 2018, doi:10.1103/PhysRevMaterials.2.019902.' short: M. Friedrich, W.G. Schmidt, A. Schindlmayr, S. Sanna, Physical Review Materials 2 (2018). date_created: 2019-09-20T11:28:23Z date_updated: 2022-01-06T06:51:35Z ddc: - '530' department: - _id: '295' - _id: '296' - _id: '230' - _id: '429' doi: 10.1103/PhysRevMaterials.2.019902 external_id: isi: - '000419778500006' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-08-28T09:11:59Z date_updated: 2020-08-30T14:34:54Z description: © 2018 American Physical Society file_id: '18536' file_name: PhysRevMaterials.2.019902.pdf file_size: 178961 relation: main_file title: 'Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)]' file_date_updated: 2020-08-30T14:34:54Z has_accepted_license: '1' intvolume: ' 2' isi: '1' issue: '1' language: - iso: eng oa: '1' project: - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '68' name: TRR 142 - Subproject B3 - _id: '69' name: TRR 142 - Subproject B4 publication: Physical Review Materials publication_identifier: eissn: - 2475-9953 publication_status: published publisher: American Physical Society quality_controlled: '1' related_material: record: - id: '10021' relation: other status: public status: public title: 'Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)]' type: journal_article user_id: '458' volume: 2 year: '2018' ... --- _id: '7481' abstract: - lang: eng text: 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. article_number: '215702' article_type: original author: - first_name: Arthur full_name: Riefer, Arthur last_name: Riefer - first_name: Nils full_name: Weber, Nils last_name: Weber - first_name: Johannes full_name: Mund, Johannes last_name: Mund - first_name: Dmitri R. full_name: Yakovlev, Dmitri R. last_name: Yakovlev - first_name: Manfred full_name: Bayer, Manfred last_name: Bayer - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Cedrik full_name: Meier, Cedrik id: '20798' last_name: Meier orcid: https://orcid.org/0000-0002-3787-3572 - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 citation: ama: 'Riefer A, Weber N, Mund J, et al. Zn–VI quasiparticle gaps and optical spectra from many-body calculations. Journal of Physics: Condensed Matter. 2017;29(21). doi:10.1088/1361-648x/aa6b2a' apa: 'Riefer, A., Weber, N., Mund, J., Yakovlev, D. R., Bayer, M., Schindlmayr, A., … Schmidt, W. G. (2017). Zn–VI quasiparticle gaps and optical spectra from many-body calculations. Journal of Physics: Condensed Matter, 29(21). https://doi.org/10.1088/1361-648x/aa6b2a' bibtex: '@article{Riefer_Weber_Mund_Yakovlev_Bayer_Schindlmayr_Meier_Schmidt_2017, title={Zn–VI quasiparticle gaps and optical spectra from many-body calculations}, volume={29}, DOI={10.1088/1361-648x/aa6b2a}, number={21215702}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Riefer, Arthur and Weber, Nils and Mund, Johannes and Yakovlev, Dmitri R. and Bayer, Manfred and Schindlmayr, Arno and Meier, Cedrik and Schmidt, Wolf Gero}, year={2017} }' chicago: 'Riefer, Arthur, Nils Weber, Johannes Mund, Dmitri R. Yakovlev, Manfred Bayer, Arno Schindlmayr, Cedrik Meier, and Wolf Gero Schmidt. “Zn–VI Quasiparticle Gaps and Optical Spectra from Many-Body Calculations.” Journal of Physics: Condensed Matter 29, no. 21 (2017). https://doi.org/10.1088/1361-648x/aa6b2a.' ieee: 'A. Riefer et al., “Zn–VI quasiparticle gaps and optical spectra from many-body calculations,” Journal of Physics: Condensed Matter, vol. 29, no. 21, 2017.' mla: 'Riefer, Arthur, et al. “Zn–VI Quasiparticle Gaps and Optical Spectra from Many-Body Calculations.” Journal of Physics: Condensed Matter, vol. 29, no. 21, 215702, IOP Publishing, 2017, doi:10.1088/1361-648x/aa6b2a.' short: 'A. Riefer, N. Weber, J. Mund, D.R. Yakovlev, M. Bayer, A. Schindlmayr, C. Meier, W.G. Schmidt, Journal of Physics: Condensed Matter 29 (2017).' date_created: 2019-02-04T13:46:58Z date_updated: 2022-01-06T07:03:39Z ddc: - '530' department: - _id: '287' - _id: '295' - _id: '296' - _id: '230' - _id: '429' doi: 10.1088/1361-648x/aa6b2a external_id: isi: - '000400093100001' pmid: - '28374685' file: - access_level: closed content_type: application/pdf creator: schindlm date_created: 2020-08-28T14:01:15Z date_updated: 2020-08-30T14:34:08Z description: © 2017 IOP Publishing Ltd file_id: '18574' file_name: Riefer_2017_J._Phys. _Condens._Matter_29_215702.pdf file_size: 2551657 relation: main_file title: Zn–VI quasiparticle gaps and optical spectra from many-body calculations file_date_updated: 2020-08-30T14:34:08Z has_accepted_license: '1' intvolume: ' 29' isi: '1' issue: '21' language: - iso: eng pmid: '1' project: - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '66' name: TRR 142 - Subproject B1 - _id: '69' name: TRR 142 - Subproject B4 - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing publication: 'Journal of Physics: Condensed Matter' publication_identifier: eissn: - 1361-648X issn: - 0953-8984 publication_status: published publisher: IOP Publishing quality_controlled: '1' status: public title: Zn–VI quasiparticle gaps and optical spectra from many-body calculations type: journal_article user_id: '458' volume: 29 year: '2017' ... --- _id: '13416' abstract: - lang: eng text: '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.' article_number: '054406' article_type: original author: - first_name: Michael full_name: Friedrich, Michael last_name: Friedrich - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Simone full_name: Sanna, Simone last_name: Sanna citation: ama: Friedrich M, Schmidt WG, Schindlmayr A, Sanna S. Polaron optical absorption in congruent lithium niobate from time-dependent density-functional theory. Physical Review Materials. 2017;1(5). doi:10.1103/PhysRevMaterials.1.054406 apa: Friedrich, M., Schmidt, W. G., Schindlmayr, A., & Sanna, S. (2017). Polaron optical absorption in congruent lithium niobate from time-dependent density-functional theory. Physical Review Materials, 1(5). https://doi.org/10.1103/PhysRevMaterials.1.054406 bibtex: '@article{Friedrich_Schmidt_Schindlmayr_Sanna_2017, title={Polaron optical absorption in congruent lithium niobate from time-dependent density-functional theory}, volume={1}, DOI={10.1103/PhysRevMaterials.1.054406}, number={5054406}, journal={Physical Review Materials}, publisher={American Physical Society}, author={Friedrich, Michael and Schmidt, Wolf Gero and Schindlmayr, Arno and Sanna, Simone}, year={2017} }' chicago: Friedrich, Michael, Wolf Gero Schmidt, Arno Schindlmayr, and Simone Sanna. “Polaron Optical Absorption in Congruent Lithium Niobate from Time-Dependent Density-Functional Theory.” Physical Review Materials 1, no. 5 (2017). https://doi.org/10.1103/PhysRevMaterials.1.054406. ieee: M. Friedrich, W. G. Schmidt, A. Schindlmayr, and S. Sanna, “Polaron optical absorption in congruent lithium niobate from time-dependent density-functional theory,” Physical Review Materials, vol. 1, no. 5, 2017. mla: Friedrich, Michael, et al. “Polaron Optical Absorption in Congruent Lithium Niobate from Time-Dependent Density-Functional Theory.” Physical Review Materials, vol. 1, no. 5, 054406, American Physical Society, 2017, doi:10.1103/PhysRevMaterials.1.054406. short: M. Friedrich, W.G. Schmidt, A. Schindlmayr, S. Sanna, Physical Review Materials 1 (2017). date_created: 2019-09-20T11:54:25Z date_updated: 2022-01-06T06:51:35Z ddc: - '530' department: - _id: '296' - _id: '295' - _id: '230' - _id: '429' doi: 10.1103/PhysRevMaterials.1.054406 external_id: isi: - '000416586100003' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-08-27T19:43:49Z date_updated: 2020-08-30T14:38:50Z description: © 2017 American Physical Society file_id: '18468' file_name: PhysRevMaterials.1.054406.pdf file_size: 1417182 relation: main_file title: Polaron optical absorption in congruent lithium niobate from time-dependent density-functional theory file_date_updated: 2020-08-30T14:38:50Z has_accepted_license: '1' intvolume: ' 1' isi: '1' issue: '5' language: - iso: eng oa: '1' project: - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '68' name: TRR 142 - Subproject B3 - _id: '69' name: TRR 142 - Subproject B4 publication: Physical Review Materials publication_identifier: eissn: - 2475-9953 publication_status: published publisher: American Physical Society quality_controlled: '1' status: public title: Polaron optical absorption in congruent lithium niobate from time-dependent density-functional theory type: journal_article user_id: '458' volume: 1 year: '2017' ... --- _id: '10021' abstract: - lang: eng text: 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. article_number: '034401' article_type: original author: - first_name: Michael full_name: Friedrich, Michael last_name: Friedrich - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Simone full_name: Sanna, Simone last_name: Sanna citation: ama: Friedrich M, Schmidt WG, Schindlmayr A, Sanna S. Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory. Physical Review Materials. 2017;1(3). doi:10.1103/PhysRevMaterials.1.034401 apa: Friedrich, M., Schmidt, W. G., Schindlmayr, A., & Sanna, S. (2017). Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory. Physical Review Materials, 1(3). https://doi.org/10.1103/PhysRevMaterials.1.034401 bibtex: '@article{Friedrich_Schmidt_Schindlmayr_Sanna_2017, title={Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory}, volume={1}, DOI={10.1103/PhysRevMaterials.1.034401}, number={3034401}, journal={Physical Review Materials}, publisher={American Physical Society}, author={Friedrich, Michael and Schmidt, Wolf Gero and Schindlmayr, Arno and Sanna, Simone}, year={2017} }' chicago: Friedrich, Michael, Wolf Gero Schmidt, Arno Schindlmayr, and Simone Sanna. “Optical Properties of Titanium-Doped Lithium Niobate from Time-Dependent Density-Functional Theory.” Physical Review Materials 1, no. 3 (2017). https://doi.org/10.1103/PhysRevMaterials.1.034401. ieee: M. Friedrich, W. G. Schmidt, A. Schindlmayr, and S. Sanna, “Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory,” Physical Review Materials, vol. 1, no. 3, 2017. mla: Friedrich, Michael, et al. “Optical Properties of Titanium-Doped Lithium Niobate from Time-Dependent Density-Functional Theory.” Physical Review Materials, vol. 1, no. 3, 034401, American Physical Society, 2017, doi:10.1103/PhysRevMaterials.1.034401. short: M. Friedrich, W.G. Schmidt, A. Schindlmayr, S. Sanna, Physical Review Materials 1 (2017). date_created: 2019-05-29T07:42:33Z date_updated: 2022-01-06T06:51:35Z ddc: - '530' department: - _id: '295' - _id: '296' - _id: '230' - _id: '429' doi: 10.1103/PhysRevMaterials.1.034401 external_id: isi: - '000416562300001' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-08-27T19:39:54Z date_updated: 2020-08-30T14:36:11Z description: © 2017 American Physical Society file_id: '18467' file_name: PhysRevMaterials.1.034401.pdf file_size: 708075 relation: main_file title: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory file_date_updated: 2020-08-30T14:36:11Z has_accepted_license: '1' intvolume: ' 1' isi: '1' issue: '3' language: - iso: eng oa: '1' project: - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 - _id: '68' name: TRR 142 - Subproject B3 publication: Physical Review Materials publication_identifier: issn: - 2475-9953 publication_status: published publisher: American Physical Society quality_controlled: '1' related_material: record: - id: '13410' relation: other status: public status: public title: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory type: journal_article user_id: '458' volume: 1 year: '2017' ... --- _id: '10023' abstract: - lang: eng text: 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. article_number: '3981317' article_type: original author: - first_name: Falko full_name: Schmidt, Falko id: '35251' last_name: Schmidt orcid: 0000-0002-5071-5528 - first_name: Marc full_name: Landmann, Marc last_name: Landmann - first_name: Eva full_name: Rauls, Eva last_name: Rauls - first_name: Nicola full_name: Argiolas, Nicola last_name: Argiolas - first_name: Simone full_name: Sanna, Simone last_name: Sanna - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X citation: ama: Schmidt F, Landmann M, Rauls E, et al. Consistent atomic geometries and electronic structure of five phases of potassium niobate from density-functional theory. Advances in Materials Science and Engineering. 2017;2017. doi:10.1155/2017/3981317 apa: Schmidt, F., Landmann, M., Rauls, E., Argiolas, N., Sanna, S., Schmidt, W. G., & Schindlmayr, A. (2017). Consistent atomic geometries and electronic structure of five phases of potassium niobate from density-functional theory. Advances in Materials Science and Engineering, 2017. https://doi.org/10.1155/2017/3981317 bibtex: '@article{Schmidt_Landmann_Rauls_Argiolas_Sanna_Schmidt_Schindlmayr_2017, title={Consistent atomic geometries and electronic structure of five phases of potassium niobate from density-functional theory}, volume={2017}, DOI={10.1155/2017/3981317}, number={3981317}, journal={Advances in Materials Science and Engineering}, publisher={Hindawi}, author={Schmidt, Falko and Landmann, Marc and Rauls, Eva and Argiolas, Nicola and Sanna, Simone and Schmidt, Wolf Gero and Schindlmayr, Arno}, year={2017} }' chicago: Schmidt, Falko, Marc Landmann, Eva Rauls, Nicola Argiolas, Simone Sanna, Wolf Gero Schmidt, and Arno Schindlmayr. “Consistent Atomic Geometries and Electronic Structure of Five Phases of Potassium Niobate from Density-Functional Theory.” Advances in Materials Science and Engineering 2017 (2017). https://doi.org/10.1155/2017/3981317. ieee: F. Schmidt et al., “Consistent atomic geometries and electronic structure of five phases of potassium niobate from density-functional theory,” Advances in Materials Science and Engineering, vol. 2017, 2017. mla: Schmidt, Falko, et al. “Consistent Atomic Geometries and Electronic Structure of Five Phases of Potassium Niobate from Density-Functional Theory.” Advances in Materials Science and Engineering, vol. 2017, 3981317, Hindawi, 2017, doi:10.1155/2017/3981317. short: F. Schmidt, M. Landmann, E. Rauls, N. Argiolas, S. Sanna, W.G. Schmidt, A. Schindlmayr, Advances in Materials Science and Engineering 2017 (2017). date_created: 2019-05-29T07:48:32Z date_updated: 2022-01-06T06:50:25Z ddc: - '530' department: - _id: '295' - _id: '296' - _id: '230' - _id: '429' doi: 10.1155/2017/3981317 external_id: isi: - '000394873300001' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-08-28T09:27:19Z date_updated: 2020-08-30T14:37:31Z description: Creative Commons Attribution 4.0 International Public License (CC BY 4.0) file_id: '18538' file_name: 3981317.pdf file_size: 985948 relation: main_file title: Consistent atomic geometries and electronic structure of five phases of potassium niobate from density-functional theory file_date_updated: 2020-08-30T14:37:31Z has_accepted_license: '1' intvolume: ' 2017' isi: '1' language: - iso: eng oa: '1' project: - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 publication: Advances in Materials Science and Engineering publication_identifier: eissn: - 1687-8442 issn: - 1687-8434 publication_status: published publisher: Hindawi quality_controlled: '1' status: public title: Consistent atomic geometries and electronic structure of five phases of potassium niobate from density-functional theory type: journal_article user_id: '458' volume: 2017 year: '2017' ... --- _id: '10024' abstract: - lang: eng text: 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. article_number: '075205' article_type: original author: - first_name: Arthur full_name: Riefer, Arthur last_name: Riefer - first_name: Michael full_name: Friedrich, Michael last_name: Friedrich - first_name: Simone full_name: Sanna, Simone last_name: Sanna - first_name: Uwe full_name: Gerstmann, Uwe id: '171' last_name: Gerstmann - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 citation: ama: 'Riefer A, Friedrich M, Sanna S, Gerstmann U, Schindlmayr A, Schmidt WG. LiNbO3 electronic structure: Many-body interactions, spin-orbit coupling, and thermal effects. Physical Review B. 2016;93(7). doi:10.1103/PhysRevB.93.075205' apa: 'Riefer, A., Friedrich, M., Sanna, S., Gerstmann, U., Schindlmayr, A., & Schmidt, W. G. (2016). LiNbO3 electronic structure: Many-body interactions, spin-orbit coupling, and thermal effects. Physical Review B, 93(7). https://doi.org/10.1103/PhysRevB.93.075205' bibtex: '@article{Riefer_Friedrich_Sanna_Gerstmann_Schindlmayr_Schmidt_2016, title={LiNbO3 electronic structure: Many-body interactions, spin-orbit coupling, and thermal effects}, volume={93}, DOI={10.1103/PhysRevB.93.075205}, number={7075205}, journal={Physical Review B}, publisher={American Physical Society}, author={Riefer, Arthur and Friedrich, Michael and Sanna, Simone and Gerstmann, Uwe and Schindlmayr, Arno and Schmidt, Wolf Gero}, year={2016} }' chicago: 'Riefer, Arthur, Michael Friedrich, Simone Sanna, Uwe Gerstmann, Arno Schindlmayr, and Wolf Gero Schmidt. “LiNbO3 Electronic Structure: Many-Body Interactions, Spin-Orbit Coupling, and Thermal Effects.” Physical Review B 93, no. 7 (2016). https://doi.org/10.1103/PhysRevB.93.075205.' ieee: 'A. Riefer, M. Friedrich, S. Sanna, U. Gerstmann, A. Schindlmayr, and W. G. Schmidt, “LiNbO3 electronic structure: Many-body interactions, spin-orbit coupling, and thermal effects,” Physical Review B, vol. 93, no. 7, 2016.' mla: 'Riefer, Arthur, et al. “LiNbO3 Electronic Structure: Many-Body Interactions, Spin-Orbit Coupling, and Thermal Effects.” Physical Review B, vol. 93, no. 7, 075205, American Physical Society, 2016, doi:10.1103/PhysRevB.93.075205.' short: A. Riefer, M. Friedrich, S. Sanna, U. Gerstmann, A. Schindlmayr, W.G. Schmidt, Physical Review B 93 (2016). date_created: 2019-05-29T07:50:59Z date_updated: 2022-01-06T06:50:26Z ddc: - '530' department: - _id: '295' - _id: '296' - _id: '230' - _id: '429' doi: 10.1103/PhysRevB.93.075205 external_id: isi: - '000370794800004' file: - access_level: open_access content_type: application/pdf creator: schindlm date_created: 2020-08-27T20:36:43Z date_updated: 2020-08-30T14:39:23Z description: © 2016 American Physical Society file_id: '18469' file_name: PhysRevB.93.075205.pdf file_size: 1314637 relation: main_file title: 'LiNbO3 electronic structure: Many-body interactions, spin-orbit coupling, and thermal effects' file_date_updated: 2020-08-30T14:39:23Z has_accepted_license: '1' intvolume: ' 93' isi: '1' issue: '7' language: - iso: eng oa: '1' project: - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 publication: Physical Review B publication_identifier: eissn: - 2469-9969 issn: - 2469-9950 publication_status: published publisher: American Physical Society quality_controlled: '1' status: public title: 'LiNbO3 electronic structure: Many-body interactions, spin-orbit coupling, and thermal effects' type: journal_article user_id: '458' volume: 93 year: '2016' ... --- _id: '10025' abstract: - lang: eng text: 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. article_type: original author: - first_name: Michael full_name: Friedrich, Michael last_name: Friedrich - first_name: Arno full_name: Schindlmayr, Arno id: '458' last_name: Schindlmayr orcid: 0000-0002-4855-071X - first_name: Wolf Gero full_name: Schmidt, Wolf Gero id: '468' last_name: Schmidt orcid: 0000-0002-2717-5076 - first_name: Simone full_name: Sanna, Simone last_name: Sanna citation: ama: Friedrich M, Schindlmayr A, Schmidt WG, Sanna S. LiTaO3 phonon dispersion and ferroelectric transition calculated from first principles. Physica Status Solidi B. 2016;253(4):683-689. doi:10.1002/pssb.201552576 apa: Friedrich, M., Schindlmayr, A., Schmidt, W. G., & Sanna, S. (2016). LiTaO3 phonon dispersion and ferroelectric transition calculated from first principles. Physica Status Solidi B, 253(4), 683–689. https://doi.org/10.1002/pssb.201552576 bibtex: '@article{Friedrich_Schindlmayr_Schmidt_Sanna_2016, title={LiTaO3 phonon dispersion and ferroelectric transition calculated from first principles}, volume={253}, DOI={10.1002/pssb.201552576}, number={4}, journal={Physica Status Solidi B}, publisher={Wiley-VCH}, author={Friedrich, Michael and Schindlmayr, Arno and Schmidt, Wolf Gero and Sanna, Simone}, year={2016}, pages={683–689} }' chicago: 'Friedrich, Michael, Arno Schindlmayr, Wolf Gero Schmidt, and Simone Sanna. “LiTaO3 Phonon Dispersion and Ferroelectric Transition Calculated from First Principles.” Physica Status Solidi B 253, no. 4 (2016): 683–89. https://doi.org/10.1002/pssb.201552576.' ieee: M. Friedrich, A. Schindlmayr, W. G. Schmidt, and S. Sanna, “LiTaO3 phonon dispersion and ferroelectric transition calculated from first principles,” Physica Status Solidi B, vol. 253, no. 4, pp. 683–689, 2016. mla: Friedrich, Michael, et al. “LiTaO3 Phonon Dispersion and Ferroelectric Transition Calculated from First Principles.” Physica Status Solidi B, vol. 253, no. 4, Wiley-VCH, 2016, pp. 683–89, doi:10.1002/pssb.201552576. short: M. Friedrich, A. Schindlmayr, W.G. Schmidt, S. Sanna, Physica Status Solidi B 253 (2016) 683–689. date_created: 2019-05-29T07:52:52Z date_updated: 2022-01-06T06:50:26Z ddc: - '530' department: - _id: '295' - _id: '296' - _id: '230' - _id: '429' doi: 10.1002/pssb.201552576 external_id: isi: - '000374142500015' file: - access_level: closed content_type: application/pdf creator: schindlm date_created: 2020-08-28T14:22:11Z date_updated: 2020-08-30T14:41:39Z description: © 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim file_id: '18577' file_name: pssb.201552576.pdf file_size: 402594 relation: main_file title: LiTaO3 phonon dispersion and ferroelectric transition calculated from first principles file_date_updated: 2020-08-30T14:41:39Z has_accepted_license: '1' intvolume: ' 253' isi: '1' issue: '4' language: - iso: eng page: 683-689 project: - _id: '52' name: Computing Resources Provided by the Paderborn Center for Parallel Computing - _id: '53' name: TRR 142 - _id: '55' name: TRR 142 - Project Area B - _id: '69' name: TRR 142 - Subproject B4 publication: Physica Status Solidi B publication_identifier: eissn: - 1521-3951 issn: - 0370-1972 publication_status: published publisher: Wiley-VCH quality_controlled: '1' status: public title: LiTaO3 phonon dispersion and ferroelectric transition calculated from first principles type: journal_article user_id: '458' volume: 253 year: '2016' ...