Scaling of the structural relaxation in simulated liquid silica

A scaling law for the alpha relaxation time tau , involving the ratio of a density-dependent energy to the thermal energy, has been found to hold in many fragile glass-forming liquids. This scaling has been recently linked to a local quantity n{loc}(rho,T) relating the variation of tau with density to its variation with temperature. In many fragile liquids, the variation of n{loc}(rho,T) is weak enough to take it as constant over the experimental temperature and density domain. We show that simulated liquid silica has an opposite behavior; close to T{g}, n{loc} is negative for moderate densities and exhibits a significant variation with rho and T, reaching positive values for higher temperature and/or densities. Moreover, those variations linearly correlate to a measure of the bonding properties of the liquid.