Large-scale density-functional calculations on silicon divacancies

We have performed total-energy electronic-structure calculations in the density-functional theory for the divacancy in Si using our real-space finite-difference pseudopotential method. Supercell models containing up to 1000 sites as well as a cluster model containing 432 atoms are used to simulate the divacancy in an otherwise perfect crystal. We have found that the resonant bond configuration is the most stable structure, the small pairing configuration is the next, and the large pairing configuration is the least stable for negatively and positively charged as well as neutral divacancies in the supercell model. The energy differences among the three configurations are found to be the order of 10 meV. Considering situations of ESR measurements, we have also performed the total-energy electronic-structure calculations under uniaxial stress along the < 110 > direction. We have found that induced strains alter the energetics and the pairing configurations become most stable with increasing strains. We argue that the ground state configuration of the Si divacancy is the resonant bond configuration and the pairing configurations become stable under the uniaxial stress and are detected by the EPR measurements.