Abstract
A new approach, called the embedded-molecular-cluster method, is proposed to calculate the electronic structure of point defects in a non-metallic crystal in the framework of the molecular cluster model. The method is applicable to defects with any perturbation radius of the crystal and is based on the concept of the latter as the sum of weakly overlapping structural elements, (atoms, ions, bonds, molecules, etc.). It accounts for Coulomb and exchange interaction between the cluster and the rest of the crystal, as well as (self-consistently) for polarisation of the latter. The present work contains a calculation of the full energy of a crystal with a point defect and arbitrary types of structural elements.