Molecular dynamics computer simulation of amorphous silica under high pressure

TL;DR

This study uses molecular dynamics simulations to explore how amorphous silica's structure and dynamics change under high pressure, revealing a transition from tetrahedral to higher-coordination networks and a maximum in diffusion at 20 GPa.

Contribution

It demonstrates the effectiveness of the CHIK potential in reproducing experimental properties of silica under high pressure and details structural transformations and diffusion behavior.

Findings

Structural transition from tetrahedral to higher coordination with increasing pressure

Shift of diffraction peaks indicating structural changes

Maximum in self-diffusion constant around 20 GPa

Abstract

The structural and dynamic properties of silica melts under high pressure are studied using molecular dynamics (MD) computer simulation. The interactions between the ions are modeled by a pairwise-additive potential, the so-called CHIK potential, that has been recently proposed by Carre et al. The experimental equation of state is well-reproduced by the CHIK model. With increasing pressure (density), the structure changes from a tetrahedral network to a network containing a high number of five- and six-fold Si-O coordination. In the partial static structure factors, this change of the structure with increasing density is reflected by a shift of the first sharp diffraction peak towards higher wavenumbers q, eventually merging with the main peak at densities around 4.2 g/cm^3. The self-diffusion constants as a function of pressure show the experimentally-known maximum, occurring around a pressure of about 20 GPa.