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Diffusivity calculation on noble gas silica systems using first-principles molecular simulations

First-principles molecular dynamics simulations are carried out to investigate the diffusivity of noble gases dissolved in silica melts. The simulations are performed for a range of molar volumes, corresponding to pressures ranging from ambient pressure to ∼50 GPa at temperatures above the SiO2 melting point. The Chi-square merit function, weighted by the statistical certainty of the data, was used to regress the mean-square displacement against time relationship and to calculate self-diffusion coefficients for noble gases, Si, and O atoms. The results are in good agreement with the available literature data. We found that the higher the temperature and smaller the noble gas atom, the higher the diffusivity; noble gas diffusivity decreased almost linearly with the square of the atomic radius. With molar volume decreasing, the self-diffusion coefficient of small noble gases decreased, while Si and O showed an abnormal dependence on molar volume. In the temperature range simulated, the diffusivity for He, Si and O could be described by an Arrhenius equation with activation energies consistent with available experimental data within simulation accuracy.