A generalized valence bond description of vacancy and impurity states in diamond and silicon

Abstract

Generalized Valence Bond and Configuration Interaction calculations using a double zeta basis have been performed for the vacancy states of diamond and silicon and for the lithium and boron impurities in silicon. For the vacancy case it was found that the nature of the low-lying electronic states of the positive, negative and neutral charge species is easily understood in terms of simple valence bond concepts. Here the effect of symmetric distortion of the vacancy was included, but no other distortions were included. For those cases in which the ordering of the states is known, the experimental ordering is reproduced by the theoretical results. For the impurity case it is found that boron is strongly bound in a substitutional site whereas lithium is not. In both cases the states of the system can be predicted from a simple valence bond analysis. The calculated results are compared with experiment through the use of a dielectric continuum approximation to correct the energies of charged and ionic states.