Interstitial voids in silica melts and implication for argon solubility under high pressures

Molecular dynamics simulations with ab initio potential under various pressures up to 11.58 GPa have been carried out to investigate the relationship between microscopic structure and solubility of Ar in silica melts. The Voronoi diagram method is used to identify interstitial voids in the structure of silica melts. We find that (1) the radius distribution of interstitial voids generally obeys the log-normal probability function; (2) the number of available interstitial voids large enough to accommodate Ar atoms decreases with increasing pressure; (3) Ar solubility increases linearly with pressure up to about 3 GPa, where Ar solubility reaches a maximum value, and then it decreases dramatically when pressure becomes higher than 5-6 GPa. The drop of Ar solubility is a result of structural continuous change but not structural transformation. These results are in good agreement with experimental measurements.