---
_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. <i>Physical Review Materials</i>. 2019;3(5).
    doi:<a href="https://doi.org/10.1103/PhysRevMaterials.3.054401">10.1103/PhysRevMaterials.3.054401</a>
  apa: Schmidt, F., Riefer, A., Schmidt, W. G., Schindlmayr, A., Imlau, M., Dobener,
    F., Mengel, N., Chatterjee, S., &#38; Sanna, S. (2019). Quasiparticle and excitonic
    effects in the optical response of KNbO3. <i>Physical Review Materials</i>, <i>3</i>(5),
    Article 054401. <a href="https://doi.org/10.1103/PhysRevMaterials.3.054401">https://doi.org/10.1103/PhysRevMaterials.3.054401</a>
  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={<a href="https://doi.org/10.1103/PhysRevMaterials.3.054401">10.1103/PhysRevMaterials.3.054401</a>},
    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.” <i>Physical Review Materials</i>
    3, no. 5 (2019). <a href="https://doi.org/10.1103/PhysRevMaterials.3.054401">https://doi.org/10.1103/PhysRevMaterials.3.054401</a>.
  ieee: 'F. Schmidt <i>et al.</i>, “Quasiparticle and excitonic effects in the optical
    response of KNbO3,” <i>Physical Review Materials</i>, vol. 3, no. 5, Art. no.
    054401, 2019, doi: <a href="https://doi.org/10.1103/PhysRevMaterials.3.054401">10.1103/PhysRevMaterials.3.054401</a>.'
  mla: Schmidt, Falko, et al. “Quasiparticle and Excitonic Effects in the Optical
    Response of KNbO3.” <i>Physical Review Materials</i>, vol. 3, no. 5, 054401, American
    Physical Society, 2019, doi:<a href="https://doi.org/10.1103/PhysRevMaterials.3.054401">10.1103/PhysRevMaterials.3.054401</a>.
  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: '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)]. <i>Physical Review Materials</i>. 2018;2(1).
    doi:<a href="https://doi.org/10.1103/PhysRevMaterials.2.019902">10.1103/PhysRevMaterials.2.019902</a>'
  apa: 'Friedrich, M., Schmidt, W. G., Schindlmayr, A., &#38; Sanna, S. (2018). Erratum:
    Optical properties of titanium-doped lithium niobate from time-dependent density-functional
    theory [Phys. Rev. Materials 1, 034401 (2017)]. <i>Physical Review Materials</i>,
    <i>2</i>(1). <a href="https://doi.org/10.1103/PhysRevMaterials.2.019902">https://doi.org/10.1103/PhysRevMaterials.2.019902</a>'
  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={<a href="https://doi.org/10.1103/PhysRevMaterials.2.019902">10.1103/PhysRevMaterials.2.019902</a>},
    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)].” <i>Physical
    Review Materials</i> 2, no. 1 (2018). <a href="https://doi.org/10.1103/PhysRevMaterials.2.019902">https://doi.org/10.1103/PhysRevMaterials.2.019902</a>.'
  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)],” <i>Physical Review Materials</i>,
    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)].” <i>Physical Review Materials</i>, vol. 2, no. 1, 019902, American
    Physical Society, 2018, doi:<a href="https://doi.org/10.1103/PhysRevMaterials.2.019902">10.1103/PhysRevMaterials.2.019902</a>.'
  short: M. Friedrich, W.G. Schmidt, A. Schindlmayr, S. Sanna, Physical Review Materials
    2 (2018).
date_created: 2019-09-20T11:28:23Z
date_updated: 2025-12-05T10:07:07Z
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: '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. <i>Physical
    Review Materials</i>. 2017;1(5). doi:<a href="https://doi.org/10.1103/PhysRevMaterials.1.054406">10.1103/PhysRevMaterials.1.054406</a>
  apa: Friedrich, M., Schmidt, W. G., Schindlmayr, A., &#38; Sanna, S. (2017). Polaron
    optical absorption in congruent lithium niobate from time-dependent density-functional
    theory. <i>Physical Review Materials</i>, <i>1</i>(5), Article 054406. <a href="https://doi.org/10.1103/PhysRevMaterials.1.054406">https://doi.org/10.1103/PhysRevMaterials.1.054406</a>
  bibtex: '@article{Friedrich_Schmidt_Schindlmayr_Sanna_2017, title={Polaron optical
    absorption in congruent lithium niobate from time-dependent density-functional
    theory}, volume={1}, DOI={<a href="https://doi.org/10.1103/PhysRevMaterials.1.054406">10.1103/PhysRevMaterials.1.054406</a>},
    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.” <i>Physical Review Materials</i> 1, no. 5 (2017). <a href="https://doi.org/10.1103/PhysRevMaterials.1.054406">https://doi.org/10.1103/PhysRevMaterials.1.054406</a>.
  ieee: 'M. Friedrich, W. G. Schmidt, A. Schindlmayr, and S. Sanna, “Polaron optical
    absorption in congruent lithium niobate from time-dependent density-functional
    theory,” <i>Physical Review Materials</i>, vol. 1, no. 5, Art. no. 054406, 2017,
    doi: <a href="https://doi.org/10.1103/PhysRevMaterials.1.054406">10.1103/PhysRevMaterials.1.054406</a>.'
  mla: Friedrich, Michael, et al. “Polaron Optical Absorption in Congruent Lithium
    Niobate from Time-Dependent Density-Functional Theory.” <i>Physical Review Materials</i>,
    vol. 1, no. 5, 054406, American Physical Society, 2017, doi:<a href="https://doi.org/10.1103/PhysRevMaterials.1.054406">10.1103/PhysRevMaterials.1.054406</a>.
  short: M. Friedrich, W.G. Schmidt, A. Schindlmayr, S. Sanna, Physical Review Materials
    1 (2017).
date_created: 2019-09-20T11:54:25Z
date_updated: 2025-12-05T10:14:23Z
ddc:
- '530'
department:
- _id: '296'
- _id: '295'
- _id: '230'
- _id: '429'
- _id: '35'
- _id: '15'
- _id: '27'
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: '16199'
volume: 1
year: '2017'
...