Doubly positively charged oxygen vacancies in silica glass

The geometric and electronic structures of doubly positively charged oxygen vacancies in a-SiO2 are calculated. We have found four types of relaxed configurations in the amorphous matrix, corresponding to puckered and unpuckerd configurations of Si atoms of the vacancy. The predicted optical absorption strongly depends on the atomic configuration of particular center and transition energies are distributed in the range from 4.5 to 6.5 eV.