Elementary mechanisms governing the dynamics of silica

A full understanding of glasses requires an accurate atomistic picture of t he complex activated processes that constitute the low-temperature dynamics of these materials. To this end, we generate over five thousand activated events in a model silica glass, using the activation-relaxation technique; these atomistic mechanisms are analyzed and classified according to their a ctivation energies, their topological properties and their spatial extent. We find that these are collective processes, involving ten to hundreds of a toms with a continuous range of activation energies; that diffusion and rel axation occurs through the creation, annihilation and motion of single dang ling bonds; and that silicon and oxygen have essentially the same diffusivi ty. (C) 2000 American Institute of Physics. [S0021-9606(00)71402-4].