Symmetry and Spin of the Decavacancy in Crystalline Si

We report total-energy electronic-structure calculations based on the density-functional theory which clarify atomic structure, spin configuration and charge of the decavacancy V-10 in crystalline Si. We have found that V10 is a negative-U system due to substantial breathing relaxation of the surrounding atoms, which makes charge states ranging from +4 to -4 possible. We have also found that V10 exhibits various types of Jahn-Teller symmetry lowering in the atomic structure depending on the charge. Highly spin-polarized states are obtained in several charge states.