The microscopic structure of a Si vacancy was studied theoretically by using first-principles super-cell calculations. Both the standard Kohn–Sham local-density approximation scheme and the generalized Kohn–Sham screened-exchange local-density approximation scheme were used. The latter approximation was expected to improve substantially the description of electronic levels in the gap region, while providing accurate total energies and bond lengths. The present local-density approximation calculations were consistent with earlier corresponding calculations of the Si vacancy, in predicting an inward relaxation of the nearest neighbours of the vacant site. The local-density approximation calculations also predicted Jahn–Teller distortions and negative effective-U effects for charged vacancies which were in qualitative agreement with experimental results and with Watkins model. Unlike local-density approximation results, the present screened-exchange local-density approximation calculations predicted an outward relaxation and sp2 type hybridization of ions surrounding the vacancy. This slightly surprising result was attributed to removal of the systematic overbinding which was associated with the local-density approximation.

Non-Local Screened-Exchange Calculations for Defects in Semiconductors - Vacancy in Silicon. J.Lento, R.M.Nieminen: Journal of Physics - Condensed Matter, 2003, 15[25], 4387-95