Electrostatic interactions between charged defects in supercells

Most theoretical calculations for point defects employ the supercell approach. The supercell consists of a few dozen or 100 atoms of the bulk material with a single defect, and is subject to periodic boundary conditions. However, the large density and periodic arrangement of the defects introduce artifacts. They need to be corrected for to extrapolate to the isolated-defect limit. This is particularly important for electrostatic interactions between charged defects, which decay only very slowly (asymptotically like L(-1)) with increasing supercell lattice constant L. In this paper, we summarize the underlying electrostatics in condensed matter. A novel defect scheme is derived from this analysis. It overcomes limitations of previous schemes with respect to applicability, systematic improvement, and formal justification. Good performance is demonstrated for vacancies in diamond and GaAs. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim