--- _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: '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: '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: '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' ...