A study was made of the structural and dynamic characteristics of the sodium atoms inside and outside the diffusion channels of glassy Na2O-4SiO2. It was shown that, on average, neither energetic arguments nor local environment considerations could explain the increased density of sodium atoms inside the sub-space made up of the channels. It was nevertheless shown that, at low temperatures, the mean-square displacement of the sodium atoms within this sub-space was significantly larger than that of the atoms outside the channels.

Characterization of Channel Diffusion in a Sodium Tetrasilicate Glass via Molecular-Dynamics Simulations. Sunyer, E., Jund, P., Jullien, R.: Physical Review B, 2002, 65[21], 214203-5