The atomic and electronic structures of various charge states (2+, +, 0, -, 2-) of monovacancies, V, and divacancies, V2, in crystalline samples were deduced from first principles. The calculations were performed, in real space, on bulk-terminated spherical and prolate clusters that were passivated by H atoms at the boundaries. Defect-induced Jahn-Teller distortions, Jahn-Teller and relaxation energies, vacancy wave-function characteristics and hyperfine parameters were calculated and were compared with experimental data. The magnitudes of the Jahn-Teller distortions and energies were found to be smaller in Ge, than in Si, for both V and V2. Unlike the case of Si, the pairing-type distortions induced by a divacancy were not large enough to result in a deep-level crossing within the band gap. The relaxed atomic configurations of the divacancy in Ge with resonant bond type distortions were found to be slightly lower in energy than those with pairing-type distortions. The effect of the lattice constant at which the calculations were performed was found to be appreciable.

Ab Initio Investigation of Point Defects in Bulk Si and Ge using a Cluster Method. S.Öğüt, J.R.Chelikowsky: Physical Review B, 2001, 64[24], 245206 (11pp)