The Dynamics of Non-Crystalline Silica: Insight from Molecular Dynamics Computer Simulations

TL;DR

This study uses molecular dynamics simulations to explore the temperature-dependent dynamics of supercooled silica, revealing a crossover from Arrhenius to power-law behavior and confirming mode-coupling theory predictions.

Contribution

It provides detailed simulation evidence of the dynamic crossover and the applicability of mode-coupling theory to supercooled silica.

Findings

Crossover from Arrhenius to power-law diffusion with temperature

Hopping dominates low-temperature ion dynamics

Beta-relaxation obeys factorization property at low temperatures

Abstract

Using a large scale molecular dynamics computer simulation we investigate the dynamics of a supercooled melt of SiO_2. We find that with increasing temperature the temperature dependence of the diffusion constants crosses over from an Arrhenius-law, with activation energies close to the experimental values, to a power-law dependence. We show that this crossover is related to the fact that at low temperatures the dynamics of the ions is dominated by hopping processes, whereas at high temperatures it shows the continuous flow-like motion proposed by the ideal version of mode-coupling theory (MCT). Finally we show that at low temperatures the dynamics of the system in the beta-relaxation regime obeys the factorization property, in agreement with MCT.