AB INITIO MOLECULAR DYNAMICS STUDY OF DISSOLVED SiO 2 IN SUPERCRITICAL WATER

Ab initio molecular dynamics simulations of SiO 2 in supercritical water at temperatures of 900 K and 1200 K and a pressure of 1.5 GPa at concentrations of 5 wt% and 16 wt% have been carried out. The different polymeric forms SiO 4 H 4, Si 2 O 7 H 6, and Si 3 O 10 H 8 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 coefficients, vibrational spectra, and radial pair distribution functions.