First-principles study of the structure and energetics of neutral divacancies in silicon

We report a first-principles study of the structure and energetics of the simple and split divacancies in silicon. The formation energies are estimated to be 4.63 and 5.90 eV, respectively. In both cases, relaxation proceeds inwards, and clearly is important, even though the relaxation energies amount to less than about 10% of the unrelaxed formation energies, enough to change the symmetry of the local structure. The binding energy of the divacancy is dose to 2 eV. For the simple divacancy, we find the relaxed structure to be of the resonant-bond Jahn-Teller type. We also find, for both the divacancy and the split divacancy, the highest occupied states to lie close to the valence band maximum.