First-principles molecular dynamics simulations show that water (8.25 wt%) dramatically affects the transport properties of ${\mathrm{SiO}}_2$ liquid increasing the diffusivity and decreasing the viscosity by an order of magnitude. At 3000 K, the diffusivity of Si, O, and H, and the viscosity vary anomalously with pressure. Highly mobile protons make the hydrous liquid a potential superionic conductor. The predicted dynamical changes are associated with structural depolymerization and water speciation, which changes from being dominated by hydroxyls at low pressure to extended structures at high pressure.

• Received 4 January 2010

DOI:https://doi.org/10.1103/PhysRevLett.104.215901