ShakeNBreak: Identifying Ground-State Defect Structures (GRC 2022 Poster)

Poster presented at the 2022 GRC Defects in Semiconductors conference, in New Hampshire, USA.

Code docs here: https://shakenbreak.readthedocs.io/en/latest/
Paper here: https://arxiv.org/abs/2207.09862

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

For other research articles and updates, check out my website at:
https://seankavanagh.com/

Transcript

1. Irea Mosquera-Lois,‡ Seán R. Kavanagh, ‡ Aron Walsh, David O. Scanlon Identifying the Ground State Structures of Point Defects in Solids Scan for the paper link and a slideshow summary! I. Mosquera-Lois‡ & S.R. Kavanagh‡, A. Walsh, D.O. Scanlon, arXiv: 2207.09862 (2022) I. Mosquera-Lois & S.R. Kavanagh, Matter 4, 2602 10.1016/j.matt.2021.06.003 (2021) Arrigoni, M. & Madsen, G. K. H. npj Comp Mater 7, (1) 10.1038/s41524-021-00537-1 (2021) S.R. Kavanagh, D.O. Scanlon, A. Walsh, C. Freysoldt, Faraday Discuss. 10.1039/D2FD00043A (2022) Lany, S. & Zunger, A. Phys. Rev. Lett. 93, 156404 10.1103/PhysRevLett.93.156404 (2004) S.R. Kavanagh, A. Walsh, D.O. Scanlon, ACS Energy Lett. 6, 1392 10.1021/acsenergylett.1c00380 (2021) I. Mosquera-Lois‡ & S.R. Kavanagh‡, A. Walsh, D.O. Scanlon, JOSS (In Submission) (2022) The Problem: How prevalent are defect reconstructions? We see it in every material we investigated, including: Sb2 Se3 , Si, ZnO, a-TiO2 , r-TiO2 , CdTe, GaAs, CeO2 , Sb2 S3 , In2 O3 – Pretty prevalent! We find a range of physical origins for these reconstructions: Typical defect modelling approach: 1. Create ‘ideal’ defect in host supercell on known crystal site. 2. Gradient-based geometry optimisation. This initial configuration can reside in a local minimum on the potential energy surface as above for VCd in CdTe, yielding a metastable structure (Tetrahedral) instead of the true ground state arrangement (Te dimer). Standard defect supercell relaxation How important can it be? How can we obtain the correct defect structure? Reconstructions can drastically affect: o Formation energies (ΔE>1 eV) o Concentrations o Transition levels o Recombination activity o Many other properties… a -> VSb formation energy diagram with the (metastable) results obtained using the standard supercell approach (dashed faded lines), and the correct ground states identified with our method (solid lines) b -> VSb energy level diagram c -> Corresponding structures We propose a method exploiting the localised nature of defect distortions and chemical intuition to efficiently navigate the potential energy surface. a b c Standard defect calculations can yield incorrect structures Testing our approach on a range of diverse semiconductors and insulators (listed above), we find: o High prevalence of energy-lowering reconstructions for point defects, which are missed by standard defect calculations. o Robust performance (>95% success rate for all known cases) o Minimal additional computational cost, demonstrated by the range of materials and defects included in this study. o Using hybrid DFT with coarse numerical accuracy for expedient qualitative identification of defect reconstructions, followed by fully-converged calculations. Code openly-available at GitHub.com/SMTG-UCL/ShakeNBreak (Python & CLI) User-friendly, compatible with VASP, CASTEP, FHI-AIMs, Quantum Espresso, CP2K. @Kavanagh_Sean_ sean.kavanagh.19@ucl.ac.uk