A first-principles study was made of the structure and energies of simple and split di-vacancies. The formation energies were estimated to be equal to 4.63 and 5.90eV, respectively. In both cases, relaxation proceeded inwards. The relaxation energies amounted to less than some 10% of the unrelaxed formation energies, but this was enough to lead to a change in the symmetry of the local structure. The binding energy of the di-vacancy was close to 2eV. In the case of the simple di-vacancy, the relaxed structure was of resonant-bond Jahn-Teller type. For both the di-vacancy and the split di-vacancy, the highest occupied states lay close to the valence band maximum.

First-Principles Study of the Structure and Energetics of Neutral Divacancies in Silicon. H.Seong, L.J.Lewis: Physical Review B, 1996, 53[15], 9791-6