Computer simulation of diffusion in silica liquid under temperature and pressure
Department of Computational Physics, Hanoi University of Science and Technology, 1 Dai Co Viet, Hanoi, Viet Nam
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Accepted: 21 May 2013
Published online: 20 June 2013
We have studied the diffusion mechanism in silica liquid following a new approach where the diffusion rate is estimated via the rate of SiO x SiO x±1 and the mean square displacement of Si particles per SiO x SiO x±1 . Molecular dynamics simulation has been conducted for a model consisting of 1998 particles over a wide range of temperatures (3000-4500K) and pressure (from 0 to 25.75GPa). Our results show that the rate of SiO x SiO x±1 increases either with increasing the temperature or pressure. Further, we find that SiO x SiO x±1 is heterogeneously distributed through the network structure of the liquid. In particular, it is concentrated on a small section of Si particles in a low-temperature regime and at ambient pressure. The spatial localisation of SiO x SiO x±1 originates from the fact that the stable unit in low- and high-pressure regime is SiO4 and SiO6 , respectively. The major change in the diffusion mechanism under pressure or temperature concerns the change in the distribution of SiO x SiO x±1 through the network structure. It is finally shown that the spatial localisation of SiO x SiO x±1 is responsible for the dynamics heterogeneity and the diffusion anomaly for silica liquid. This finding supports the concept that as the temperature approaches the glass transition point, SiO x SiO x±1 spatially localises such that the diffusivity drops and the dynamics are anomalously slow.
Key words: Flowing Matter: Liquids and Complex Fluids
© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg, 2013