Oxygen neutral defects in silica: Origin of the distribution of the formation energies

We present a numerical study of the neutral oxygen defects in silica. This work was performed using two complementary approaches: molecular dynamics using an empirical potential and ab initio calculations. We show that the formation energy fluctuates from point to point. The dispersion is due to the fluctuations of the local stress before defect creation. Using lattice statics, we establish the relation between the local-stress fluctuations inherent in the glassy state and the formation energies.