First-principles molecular dynamics simulations were made of the liquid for mantle conditions. Liquid-state thermodynamics and diffusion were evaluated at 3000 to 6000K and pressures of 0 to 144GPa. Consistent with previous first-principles studies of polymerized liquids, it was found that a fourth-order finite-strain expansion was required in order to account for the pressure-volume equation of state. Thermodynamic properties for NaAlSi2O6 liquid, derived from the results using a self-consistent thermodynamic relationship, agreed well with experimental measurements. The computed species self-diffusivities generally decreased with pressure, except for Si and O, which increased with pressure below 16GPa at 3000K. While the self-diffusivities for Na at low pressures were almost an order of magnitude higher than for other species, this contrast in mobility disappeared at above 20GPa.

Thermodynamics, Diffusion and Structure of NaAlSi2O6 Liquid at Mantle Conditions: a First-Principles Molecular Dynamics Investigation. Ni, H., De Koker, N.: Journal of Geophysical Research B, 2011, 116[9], 09202