Density-functional theory of localized perturbations in solids

Predicting the atomic geometry induced by localized perturbations, such as defects and impurities in semiconductors and insulators, is a challenge for both theory and experiment. A good description of the coupling between the electrons and the lattice is one of the essential ingredients for a quantitative theory of such phenomena, an other ingredient being the ability to treat the electronic and the atomic degrees of freedom on the same footing. This is done in modern computational schemes based on density functional theory for the electrons combined with a molecular dynamics description of the coupled electron-atom system. In this talk some recent applications of this approach will be reviewed, covering a range of different situations such as point defects, localized excitons and localized positrons. In all cases a detailed comparison with experimental results will be given. In addition, some of the current limitations of the theory as well as some likely directions for future progress will be pointed out.