Predicting Polaronic Defect States by Means of Generalized Koopmans Density Functional Calculations

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Abstract

Lattice defects in semiconductors and wide-gap materials which create deep levels in an open-shell electronic configuration can give rise to so-called defect bound small polarons. This type of defects present a challenge for electronic structure methods because the localization of the defect state and the associated energy levels depend sensitively on the ability of the total-energy functional to satisfy the physical condition that the energy E(N) must be a piecewise linear function of the fractional electron number N. For practical applications the requirement of a linear E(N) is re-cast as a generalized Koopmans condition. Since most functionals do not fulfill this condition accurately, we use parameterized perturbations that cancel the non-linearity of E(N) and recover the correct Koopmans behavior. Starting from standard density functionals, we compare two types of parameterized perturbations, i.e., the addition of on-site potentials and the mixing of non-local Fock exchange in hybrid-functionals. Surveying a range of acceptor-type defects in II-VI and III-V semiconductors, we present a classification scheme that describes the relation between hole localization and the lattice relaxation of the polaronic state.

Original languageAmerican English
Pages (from-to)1052-1060
Number of pages9
JournalPhysica Status Solidi (B) Basic Research
Volume248
Issue number5
DOIs
StatePublished - 2011

NREL Publication Number

  • NREL/JA-5900-49226

Keywords

  • Defects
  • Density functional theory
  • Hybrid functionals
  • Polarons

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