Molecular dynamics simulations were made of glasses which contained 1.8 to 33.33mol%Na2O. The simulations showed that there was a close relationship between Na atoms and non-bridging O atoms which were located mainly in the first Na coordination-shell. Over the entire range of compositions, Na and non-bridging O atoms appeared to segregate, and give rise to an heterogeneous distribution. At higher alkali concentrations, the formation of micro-channels was observed. The activation energies for alkali diffusion were computed, and were found to be in agreement with experiment. The diffusion mechanism was also investigated, and was found to occur via the micro-channels, when present; or across the network at low compositions. The Na motion always appeared to be assisted by non-bridging O atoms.

Molecular Dynamics Simulations of (NaO2)x(SiO2)1-x Glasses: Relation between Distribution and Diffusive Behavior of Na Atoms. J.Oviedo, J.F.Sanz: Physical Review B, 1998, 58[14], 9047-53