BKS Potential Research Articles

Model of silica glass from combined classical and ab initio molecular-dynamics simulations

A Car-Parrinello (CP) molecular dynamics simulation of vitreous silica, combined with classical molecular dynamics, is presented. The equilibration of the liquid, quench and relaxation of the glass are performed classically using the van Beest, Kramer and van Santen (BKS) potential [12] and the resulting configuration (coordinates and velocities) is used as input for the CP simulation. A remarkable stability of the CP dynamics is observed justifying this procedure and validating the BKS potential. Several structural and electronic properties are calculated and compared with experiments.

Specific Heat of Amorphous Silica within the Harmonic Approximation

We investigate to what extent the specific heat of amorphous silica can be calculated within the harmonic approximation. For this we use molecular dynamics computer simulations to calculate, for a simple silica model (the BKS potential), the velocity autocorrelation function and hence an effective density of states g(ν). We find that the harmonic approximation is valid for temperatures below 300 K but starts to break down at higher temperatures. We show that, to obtain a reliable description of the low-frequency part of g(ν), i.e., where the boson peak is observed, it is essential to use large systems for the simulations and small cooling rates to quench the samples. We find that the calculated specific heat is, at low temperatures (below 50 K), about a factor of 2 smaller than the experimental one. In the temperature range 200 K ≤ T ≤ Tg, where Tg = 1450 K is the glass transition temperature, we find a very good agreement between the theoretical specific heat and the experimental one.