Calculations for electronic point defects with self-consistent lattice polarisation: the F+centre in MgO

Abstract

Describes a method for combining a quantum mechanical treatment of a cluster of ions near a point defect in an ionic crystal with self-consistent polarisation in the surrounding perfect lattice, which is described by a shell model. The authors discuss the application of this model to the F⁺ centre in MgO. They show that lattice polarisation effects are important in accurate calculations of the optical absorption and emission. They also demonstrate that small clusters of ions treated quantum mechanically are not adequate as a description of the excited state of the F⁺ centre since the diffusion electron density tends to spill over into the surrounding lattice, giving unphysical results. The authors calculations give some support to suggestions that charge transfer from second-neighbour O^2- ions is important. They discuss ways of improving the method (for example the use of pseudopotential) in the light of their results.