Molecular dynamics simulation of silicon dioxide glass

Abstract

A molecular dynamics study of the thermodynamic, structural and dynamical properties of a model silicon dioxide glass is described. The system consists of 3000 ions in a cubic volume. The results of the present simulation are compared with the results of our earlier simulation of a small system containing only 375 ions. The glass transition point is identified by a sudden change in the value of specific heat and pressure. Below this point diffusion also ceases. The structure of simulated glass is found to be a three-dimensional continuous network of SiO₄ tetrahedra, connected at the oxygen nodes with a broad distribution of Si-O-Si angle centred around 153°. Other structural features, namely radial distribution functions and the interference function, are found to be in good agreement with the experimentally observed values. The holes in this open network system are interconnected, and form a continuous network. The existing inert gas solubility data in SiO₂ glass are explained by using the hole size distribution of the simulated system. Permanent compaction in the simulated glass sample is investigated by using high compressions. Although 15% permanent compaction is achieved in the simulation, no high density polymorphs, e.g. stishovite etc., are formed. The vibrational density of states are calculated from the velocity autocorrection functions of the simulated system.