Ab initio molecular dynamics study of dissolved SiO2 in supercritical water

Ab initio molecular dynamics simulations of SiO2 in supercritical water at temperatures of 900 K and 1200 K and a pressure of 1.5 GPa at concentrations of 5wt% and 16 wt% have been carried out. The different polymeric forms SiO4H4, Si2O7H6, and Si3O10H8 are found to be energetically similar within the statistical error, suggesting that all three polymeric forms play an important role in solutions at the above conditions. However, neither spontaneous polymerization nor depolymerization has been observed during the 10-ps time span of the simulations. The dynamic and structural properties of the supercritical solutions have been analyzed in terms of diffusion coeffcients, vibrational spectra, and radial pair distribution functions.