The glass transition in a model silica glass: evolution of the local structure

We use molecular dynamics simulations and the Voronoi tessellation to study the geometrical modifications as a function of temperature in a model silica glass. The standard deviation of the cell volumes, which is a measure of the local density fluctuations, decreases with decreasing temperature, as if it would like to vanish at zero temperature. This evolution towards an ordered state is frozen out at the grass transition and consequently an amorphous sample is obtained at low temperature. This structural freezing following upon the glass transition is noticeable in all the other geometric characteristics of the Voronoi' cells and a possible interpretation in terms of geometrical frustration is proposed.