Defects in alkali-metal halide crystals

Abstract

This paper discusses classical and recent calculations of defect energies for alkali-metal halide crystals. First, the methods of deriving crystal potentials are summarized and then the application of these in the computer simulation of the lattice, using the Mott–Littleton strategy, are described. The main emphasis is on an assessment of methods and potentials in the light of comparison with experimental data. There is a need for further entropy calculations and also for improvements to the quasiharmonic approximation. Some recent calculations for a lattice in mechanical equilibrium at all temperatures are described. Selected results are given for calculations of defect formation and migration energies, for the relaxation of substitutional impurities from lattice sites, for the formation of impurity–vacancy complexes and for the clustering of impurities to form trimers and Suzuki phases.