Managing the supercell approximation for charged defects in semiconductors: Finite-size scaling, charge correction factors, the band-gap problem, and the ab initio dielectric constant

C. W. M. Castleton, A. Höglund, and S. Mirbt
Phys. Rev. B 73, 035215 – Published 25 January 2006

Abstract

The errors arising in ab initio density functional theory studies of semiconductor point defects using the supercell approximation are analyzed. It is demonstrated that (a) the leading finite size errors are inverse linear and inverse cubic in the supercell size and (b) finite size scaling over a series of supercells gives reliable isolated charged defect formation energies to around ±0.05eV. The scaled results are used to test three correction methods. The Makov-Payne method is insufficient, but combined with the scaling parameters yields an ab initio dielectric constant of 11.6±4.1 for InP. Γ point corrections for defect level dispersion are completely incorrect, even for shallow levels, but realigning the total potential in real-space between defect and bulk cells actually corrects the electrostatic defect-defect interaction errors as well. Isolated defect energies to ±0.1eV are then obtained using a 64 atom supercell, though this does not improve for larger cells. Finally, finite size scaling of known dopant levels shows how to treat the band gap problem: in 200 atom supercells with no corrections, continuing to consider levels into the theoretical conduction band (extended gap) comes closest to experiment. However, for larger cells or when supercell approximation errors are removed, a scissors scheme stretching the theoretical band gap onto the experimental one is in fact correct.

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  • Received 2 November 2005

DOI:https://doi.org/10.1103/PhysRevB.73.035215

©2006 American Physical Society

Authors & Affiliations

C. W. M. Castleton1,2,*, A. Höglund3, and S. Mirbt3

  • 1Material Physics, Materials and Semiconductor Physics Laboratory, Royal Institute of Technology (KTH), Electrum 229, SE-16440 Kista, Sweden
  • 2Department of Physical Electronics/Photonics, ITM, Mid Sweden University, SE-85170 Sundsvall, Sweden
  • 3Theory of Condensed Matter, Department of Physics, Uppsala University, Box 530, SE-75121 Uppsala, Sweden

  • *Present address: Materials Chemistry, Box 538, SE-75121 Uppsala, Sweden. Email address: Christopher.Castleton@mkem.uu.se

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Vol. 73, Iss. 3 — 15 January 2006

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