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ShakeNBreak: Symmetry-Breaking and Reconstruction at Defects in Solids

ShakeNBreak: Symmetry-Breaking and Reconstruction at Defects in Solids

Pre-recording of my talk 'Symmetry-Breaking and Reconstruction at Defects in Solids' at APS March 2023 in Las Vegas, USA – discussing the issue of global optimisation for defects in solids, its importance and our work (ShakeNBreak) on tackling this issue.

Talk recording on YouTube: https://youtu.be/aqXlyLofLSU

ShakeNBreak website: https://shakenbreak.readthedocs.io/en/latest/

Our general defect calculation package doped is available here: https://github.com/SMTG-UCL/doped

See our open-access papers on defect structure-searching here:
https://www.nature.com/articles/s41524-023-00973-1
https://joss.theoj.org/papers/10.21105/joss.04817

For other talks on YouTube, have a look at my channel!
For other research articles see:
https://bit.ly/3pBMxOG

Slides for my talks can be found here:
https://speakerdeck.com/kavanase

Other references:
Matter Preview of Defect Structure Searching: https://www.sciencedirect.com/science/article/pii/S2590238521002733
Metastable defects : https://doi.org/10.1039/D2FD00043A
Recombination at V_Cd in CdTe (case study): https://pubs.acs.org/doi/abs/10.1021/acsenergylett.1c00380

Seán R. Kavanagh

March 19, 2023
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Transcript

  1. Standard defect supercell relaxation
    Seán R. Kavanagh‡ & Irea Mosquera-Lois,‡
    Aron Walsh, David O. Scanlon
    APS March 2023
    I. Mosquera-Lois‡ & S. R. Kavanagh‡*, A. Walsh and D. O. Scanlon*,
    npj Comput Mater, 2023, 9, 1–11
    Identifying the Ground State
    Structures of Point Defects in Solids

    View Slide

  2. Standard defect supercell relaxation
    Identifying the Ground State
    Structures of Point Defects in Solids
    Seán R. Kavanagh‡ & Irea Mosquera-Lois,‡
    Aron Walsh, David O. Scanlon
    APS March 2023
    I. Mosquera-Lois‡ & S. R. Kavanagh‡*, A. Walsh and D. O. Scanlon*,
    npj Comput Mater, 2023, 9, 1–11

    View Slide

  3. Defect Calculation Workflow
    3
    Host primitive cell
    Goyal et al, Comp Mater Sci 2017

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  4. Defect Calculation Workflow
    4
    Host primitive cell
    Goyal et al, Comp Mater Sci 2017

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  5. Defect Calculation Workflow
    5

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  6. Defect Calculation Workflow
    6

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  7. Defect Calculation Workflow
    7

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  8. Defect Calculation Workflow
    8

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  9. Defect Calculation Workflow
    9

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  10. Defect Calculation Workflow
    10

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  11. Defect Calculation Workflow
    11
    ➡ Energy
    ➡ Concentration
    ➡ Transition Level
    ➡ Deep/Shallow
    ➡ Doping
    ➡ Carrier capture
    ➡ Diffusion
    ➡ …

    View Slide

  12. VCd
    in CdTe

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  13. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    VCd
    in CdTe

    View Slide

  14. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    VCd
    in CdTe

    View Slide

  15. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    VCd
    in CdTe

    View Slide

  16. VCd
    in CdTe Tei
    in CdTe
    Standard Relaxation
    ShakeNBreak
    (Our Method)

    View Slide

  17. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    Kavanagh, Walsh, Scanlon
    ACS Energy Lett 2021
    VCd
    in CdTe

    View Slide

  18. Metal-metal dimers possible for vacancies in semiconductors:
    Lany & Zunger Phys Rev Lett 2004
    Lany & Zunger Phys Rev B 2005
    Kavanagh, Walsh, Scanlon
    ACS Energy Lett 2021
    VCd
    in CdTe

    View Slide

  19. Potentially the Wrong Defect!
    Mosquera-Lois & Kavanagh* Matter 2021
    Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    Mosquera-Lois‡ & Kavanagh‡*, Walsh and Scanlon*
    npj Comput Mater 2023
    Standard defect supercell relaxation

    View Slide

  20. How Prevalent is This?
    Tested on a diverse range of materials: Si, CdTe, GaAs, Sb2
    S3
    , Sb2
    Se3
    , CeO2
    , In2
    O3
    , ZnO, anatase-TiO2
    Energy-lowering reconstructions, missed by standard relaxations, found in every material studied
    Mosquera-Lois‡ & Kavanagh‡*, Walsh and Scanlon* npj Comput Mater 2023

    View Slide

  21. Defect Calculation Workflow
    21

    View Slide

  22. How Important is This?
    Kavanagh*, Scanlon, Walsh, Freysoldt Faraday Discussions 2022
    Inaccurate Structure ➡ Inaccurate Formation Energy ➡ Inaccurate:
    ➡ Energy
    ➡ Concentration
    ➡ Transition Level
    ➡ Deep/Shallow
    ➡ Doping
    ➡ Carrier capture
    ➡ Diffusion
    ➡ …

    View Slide

  23. How Important is This? Very
    Standard Relaxation
    (Metastable)
    Example: Vacancies in Sb2
    Se3
    /Sb2
    S3
    Reveals rare 4-electron negative-U behavior and ultra-
    strong self-compensation in Sb2
    S3
    & Sb2
    Se3
    Difference in predicted VSb
    concentration = 1021
    Our Method
    (Ground-state)
    Wang, Kavanagh, Scanlon, Walsh;
    ‘Four-electron Negative-U Vacancy Defects in Antimony Selenide’
    Under Review at Phys Rev Lett (arXiv: 2302.04901)

    View Slide

  24. How Important/Prevalent is This? Very
    Further Examples:
    • Gallium vacancies, migration and compensation in Ga2
    O3
    1
    • Catalytic activity (divalent metal dopants in CeO2
    )2
    • CdTe solar cell performance3
    • Defect absorption / bandgap lowering (Sn-doped Cs3
    Bi2
    Br9
    )4
    • Persistent Photoconductivity in Si, GaAs DX centres1,5
    • Oxide polarons (in BiVO4
    )6
    • Colour centres and deep anion vacancies in II-VI compounds7
    1. Varley et al J. Phys.: Condens. Matter 2011
    2. Kehoe, Scanlon, Watson, Chem Mater 2011
    3. Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    4. Krajewska, Kavanagh et al. Chem Sci 2021
    5. Du & Zhang Phys Rev B 2005
    6. Osterbacka, Ambrosio, Wiktor J Phys Chem C 2022
    7. Lany & Zunger Phys Rev Lett 2004
    Inaccurate Structure ➡ Inaccurate Formation Energy ➡
    Inaccurate:
    ➡ Energy
    ➡ Concentration
    ➡ Transition Level
    ➡ Deep/Shallow
    ➡ Doping
    ➡ Carrier capture
    ➡ Diffusion
    ➡ …

    View Slide

  25. Structure Searching Strategies
    1. Electron attractor method
    2. Random sampling
    3. Evolutionary Algorithm
    ➡ Good for polaronic defects (but only polaronic defects)
    ➡ Guaranteed to find the ground-state, eventually…
    ➡ Can be enhanced with ML models
    Pham & Deskins, J Chem Theory Comp 2021
    Huang, M. et al. J. Semicond 2022
    Pickard & Needs. Phys Rev Lett 2006
    Morris, Pickard, Needs. Phys Rev B 2008
    Morris, Pickard, Needs. Phys Rev B 2009
    Arrigoni & Madsen npj Comp Mater 2021
    ➡ Significant manual effort (setup & hyperparameter tuning)
    ➡ Inefficient
    ➡ Require many calculations so typically only possible
    with cheap inaccurate levels of theory (semi-local DFT)
    ➡ Infeasible for typical full defect studies
    Further details in: Mosquera-Lois‡ & Kavanagh‡*, Walsh and Scanlon* npj Comput Mater 2023

    View Slide

  26. Our Method: ShakeNBreak
    Idea: Leverage the localised “molecule-in-a-solid”
    behaviour of point defects:
    • Chemically-guided neighbour bond distortions:
    No. distorted bonds = Δ{Valence Electrons}
    • Stretch/compress neighbour bonds (±60% range)
    ➡ Distortion mesh of trial structures
    • ‘Rattle’: Add small random displacements to break
    symmetry and aid location of global minimum
    • Relax
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon*; npj Comp Mater 2023
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon*; J. Open Source Software 2022

    View Slide

  27. ShakeNBreak
    11 relaxations with 𝚪-only sampling
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022

    View Slide

  28. ShakeNBreak
    11 relaxations with 𝚪-only sampling
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022

    View Slide

  29. 11 relaxations with 𝚪-only sampling
    ShakeNBreak
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022

    View Slide

  30. 11 relaxations with 𝚪-only sampling
    ShakeNBreak
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022

    View Slide

  31. 11 relaxations with 𝚪-only sampling
    (Spin-Unpolarised for simplicity)
    ShakeNBreak
    :

    View Slide

  32. Successfully reproduces all previously-reported cases (so far!)
    (Benchmarks: Si, CdTe, GaAs, CeO2
    , ZnO…)
    Energy-lowering reconstructions identified in a diverse
    range of materials & defects
    (Sb2
    S3
    /Sb2
    Se3
    , In2
    O3
    , TiO2
    , Si, CdTe, GaAs, CeO2
    , ZnO)
    Can locate low-energy metastable structures
    ➡ Important for diffusion (transition states) and carrier
    recombination.3-5
    Efficient (<10% computational cost of full defect study)
    Automated & super user-friendly (Python API or CLI),
    trivially parallel…
    ShakeNBreak
    1. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon*; npj Comp Mater 2023
    2. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon*; J. Open Source Software 2022
    3. Alkauskas et al. Phys. Rev. B, 2016
    4. Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    5. Kavanagh*, Scanlon, Walsh, Freysoldt; Faraday Discussions 2022
    :

    View Slide

  33. Sneak Preview:
    Slide Credit: Aron Walsh (Defects Seminar/Invited Talks 2023)
    Example: VO
    +1 in Na2
    TiSiO5
    Collaboration w/Prof. Yu Kumagai @
    Tohoku University, Japan
    High-throughput search for symmetry-
    breaking at oxygen vacancies
    >200 oxides calculated so far
    Empirically, symmetry-breaking
    particularly likely with:
    - Multinary composition
    - Reduced crystal symmetry
    - Mixed ionic/covalent bonding
    (i.e. more complex potential energy
    surface, as expected)

    View Slide

  34. Acknowledgements
    Profs David Scanlon & Aron Walsh
    Irea Mosquera-Lois
    Studies using ShakeNBreak (and finding lower energy defect structures):
    • X. Wang, S. R. Kavanagh, D. O. Scanlon, A. Walsh; Under Review at Phys Rev Lett (arXiv: 2302.04901)
    • C. Krajewska, S. R. Kavanagh et al. Chem Sci
    • S. R. Kavanagh*, D. O. Scanlon, A. Walsh, C. Freysoldt Faraday Discussions
    • J. Cen et al; Under Review at J. Mater. Chem. A, (ChemRxiv: 10.26434/chemrxiv-2023-nk8lr)
    • J. Willis, Q. Zhou et al. In preparation.
    • Y. T. Huang & S. R. Kavanagh et al. Nature Communications
    • A. Nicolson et al; In preparation – ChemRxiv next week!
    • Y. Kumagai et al; In submission
    • A. Samli et al;. In preparation

    View Slide

  35. Key Takeaways
    • Obtaining the correct defect structure
    is important!
    • Our current procedure for defect
    calculations is incomplete
    • Energy-lowering reconstructions
    prevalent in a wide & diverse
    range of materials/defects.
    • ShakeNBreak = easily-implemented
    method to combat this and ensure the
    accuracy of defect calculations
    @Kavanagh_Sean_ [email protected]
    1. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    2. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022
    3. Mosquera-Lois & Kavanagh*, Matter 2021
    4. Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    5. Kavanagh*, Scanlon, Walsh, Freysoldt; Faraday Discussions 2022
    Catch me at Tuesday’s poster session for more discussion!

    View Slide

  36. Key Takeaways
    • Obtaining the correct defect structure
    is important!
    • Our current procedure for defect
    calculations is incomplete
    • Energy-lowering reconstructions
    prevalent in a wide & diverse
    range of materials/defects.
    • ShakeNBreak = easily-implemented
    method to combat this and ensure the
    accuracy of defect calculations
    @Kavanagh_Sean_ [email protected]
    1. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* npj Comp Mater 2023
    2. Mosquera-Lois‡ & Kavanagh‡*, Walsh, Scanlon* J. Open Source Software 2022
    3. Mosquera-Lois & Kavanagh*, Matter 2021
    4. Kavanagh, Walsh, Scanlon ACS Energy Lett 2021
    5. Kavanagh*, Scanlon, Walsh, Freysoldt; Faraday Discussions 2022

    View Slide

  37. How Important is This? Very
    VCd
    -1
    VCd
    0
    h+ e-
    Our Method
    (Ground-state)
    Standard Relaxation
    (Metastable)
    h+ capture
    e– capture
    h+ capture
    e– capture
    Kavanagh, Walsh, Scanlon
    ACS Energy Lett 2021
    Inaccurate Structure ➡ Inaccurate Formation Energy ➡
    Inaccurate:
    ➡ Energy
    ➡ Concentration
    ➡ Transition Level
    ➡ Deep/Shallow
    ➡ Doping
    ➡ Carrier capture
    ➡ Diffusion
    ➡ …

    View Slide

  38. Why isn’t this an issue for bulk structure prediction?
    Good initial guesses from experimental databases, starting us close to the global minimum
    For unknown crystal structure prediction,
    this is a huge avenue of research
    Ø PES exploration
    But defects are unknown structures!
    No database of known defect structures
    Ø Efficient structure-searching techniques
    required

    View Slide

  39. Parameter Testing
    Tip of the iceberg…

    View Slide

  40. View Slide