Molecular dynamics simulations of porous silica

We describe a new simulation method for the preparation of porous silica and present results from molecular dynamics simulations of the structures obtained. We start from a homogeneous liquid phase with reduced atomic charges. The charges are then slowly rescaled and the atoms start clustering to finally form a porous network. We observe that local ordering precedes formation of long range correlations. We investigate physical properties of porous silica such as porosity, internal surface and fractality. They are in reasonable agreement with experimental data, although internal surface and porosity seem to be systematically larger than those found in adsorption experiments. The vibrational and dielectric power spectra show an enhanced intensity in the low frequency region. These modes can be associated with slow dynamics of clusters.