The +1 charged state of an O vacancy V(O)+ in α-quartz was found to be unstable with respect to the reaction 2V(O)+ → V(O)0 + V(O)2+, which lowers the total energy by 2.9eV, making it highly unlikely that V(O)+ was the source of the electron-paramagnetic-resonance active E11 center in α-quartz. Results from ab initio total energy calculations indicated that V(SiO3)+ and V(SiO4)+ were the smallest electron paramagnetic resonance active vacancy complexes. The atomic and electronic structures of these two multi-vacancy clusters were surprisingly similar to those of V(O)+.

Negative-U Property of the Oxygen Vacancy Defect in SiO2 and its Implication for the E11 Center in α-Quartz. D.J.Chadi: Applied Physics Letters, 2003, 83[3], 437-9