Ab initio molecular dynamics study of elasticity of akimotoite MgSiO3 at mantle conditions

摘要

The thermo-elastic properties of MgSiO3 akimotoite at mantle pressure and temperature conditions are reported based on ab initio molecular dynamic simulations. A third-order Birch-Murnaghan equation at a reference temperature of 2000 K is defined by K-0 = 158 GPa, K-0'= 3.7, G(0) = 85.7 GPa, G(0)' = 4.5, V-0(2000K)=1100.54 angstrom(3), the Gruneisen parameter is determined to be gamma(V)=gamma(0)(V/V-0(2000K))(q) with gamma(0) = 1.84 and q = 1.84, with V(2000 K) = 1048.22 angstrom(3). An implied pressure correction is -7.6GPa in these parameters due to GGA overestimates the pressure. The thermal expansion is determined to be alpha/alpha(0) = (V/V-0(2000 K))(delta T) in which alpha(0) = 3.21 x 10(-5) K-1 and delta(T) = 4.6. Akimotoite may be stable above the 660 discontinuity in relatively low temperature or low aluminium environments. The high velocity and elastic anisotropy of akimotoite provide diagnostics for its presence above the 660 km discontinuity. Published by Elsevier B.V.