Mg2SiO4 liquid under high pressure from molecular dynamics

We use a flexible potential model to perform large-scale molecular dynamics simulations of Mg2SiO4 melt up to pressures of 24GPa and at temperatures between 2390K and 3200K. We find that thermal pressure and the Gruneisen parameter gamma increase linearly with density, independent on temperature. gamma increases from 0.5 at ambient pressure to 0.75 at 24CPa. While Si stays overwhelmingly in tetrahedral coordination, the coordination of Mg increases significantly under compression, from an average 5-fold coordination at room pressure to 7-fold Coordination at 24GPa. Medium range order in Mg2SiO4 as expressed by X-ray and neutron structure factors change considerably with pressure, with features at low wave-vectors q sharpening considerably and shifting to higher q. Diffusivity of the atomic species in Mg2SiO4 decrease uniformly with pressure and are well described by an Arrhenius law. For viscosity eta we find good agreement with experiments at room pressure, and predict a rapid increase with pressure. (c) 2008 Elsevier B.V. All rights reserved.