A quasi-cluster embedding scheme was used to calculate the ground-state potential surfaces, energies and probabilities of electronic transitions in neutral and charged point defects in these crystals. The model was closely related to the periodic super-cell and molecular cluster approaches. Two modified versions of the model were proposed which improved the results of calculations of the ground-state properties (especially for small quasi-clusters) and transition energies. It was noted that the ground-state potential surfaces which were calculated for defects in ionic and semi-ionic crystals were superior to those which were obtained by using super-cell and molecular cluster models.

S.A.Titov: Physica Status Solidi B, 1995, 190[1], 261-70