First-principles atomic and electronic structures of neutral (V20) and charged (V2+, V2-, V22-) Si divacancies were investigated by using bulk-terminated clusters with up to about 320 Si atoms. For the first time, the relaxed structures of V2+, V20 and V2- were found to exhibit large pairing Jahn-Teller distortions which were consistent with electron paramagnetic resonance experiments. Atomic relaxations, Jahn-Teller and relaxation energies, and hyperfine parameters were calculated for various charge states, and were compared with available experimental data. It was concluded that the cluster size, and the anisotropic nature of the relaxation, played key roles in establishing the stability of structures with large pairing distortions.

Large Pairing Jahn-Teller Distortions around Divacancies in Crystalline Silicon S.Oğüt, J.R.Chelikowsky: Physical Review Letters, 1999, 83[19], 3852-9