Elastic properties of MgSiO3-perovskite under lower mantle conditions and the composition of the deep Earth

- Systematic errors from DFT can be eliminated with a generalized rescaling method.
- The shear modulus depends less strongly on temperature than previous estimations.
- Anharmonicity can be quantified through molecular dynamics trajectory.
- Pyrolite provide a good fit to the wave velocities in most of lower mantle regime.

Elastic properties of MgSiO3-perovskite are of fundamental importance for our understanding of the thermal and chemical state of the lower mantle. However, the elastic moduli and especially their derivatives with respect to temperature and pressure at lower mantle conditions are still uncertain. In this study, we have carried out extensive first principles molecular dynamics simulations to determine the equation of state, elastic constants, moduli and velocities of MgSiO3-perovskite over a wide temperature and pressure regime (from static conditions to 3500 K and from 36 GPa to 140 GPa). Systematic errors arising from approximations to the exchange-correlation functional in density functional theory have been essentially eliminated with a generalized re-scaling method. Molecular dynamics trajectories were carefully converged with respect to duration and system size and analyzed to distinguish the effects of anharmonicity. Based on the new elastic properties derived in this study, the pyrolite mineralogical model is found to predict wave velocities in close agreement with those of seismic observations in most of lower mantle regime.