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

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 K0 = 158 GPa, K′0=3.7K′0=3.7, G0 = 85.7 GPa, G′0=4.5G′0=4.5, V0(2000 K) = 1100.54 Å3, the Grűneisen parameter is determined to be γ(V) = γ0(V/V0(2000 K))q with γ0 = 1.84 and q = 1.84, with V(2000 K) = 1048.22 Å3. An implied pressure correction is −7.6 GPa in these parameters due to GGA overestimates the pressure. The thermal expansion is determined to be α/α0=(V/V0(2000 K))δTα/α0=(V/V0(2000 K))δT in which α0 = 3.21 × 10−5 K−1 and δT = 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.