Triplet states at an O vacancy in α-quartz

The energy landscape of an α-quartz O vacancy in the lowest triplet state is investigated. Four local minima are identified and geometries, total energies, and electron paramagnetic resonance (EPR) parameters are obtained. On the basis of calculated values for the magnetic dipole interaction between the electrons two of the structures are identified with known triplet centers detected by EPR. The effect of Ge substitution is studied, and it is concluded that Ge impurities in silica act as traps for dangling bonds with a trapping energy of $\sim 1.5\hspace{0.5em}\mathrm{eV}$ relative to Si ions.