Irea Mosquera-Lois,‡ Seán R. Kavanagh, ‡ Aron Walsh, David O. Scanlon
Identifying the Ground State Structures of Point Defects in Solids
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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_ [email protected]