Melting curves of MgSiO3 and CaSiO3 perovskites with cubic structure at extreme conditions

Abstract

In this work, we derive the analytical expression of Helmholtz free energy, mean nearest neighbor distance between two atoms, lattice constant, and molar volume using statistical moment method (SMM). Then, we present how to determine the melting temperature of cubic perovskite at high pressures by combining SMM and work-heat equivalence principle. The results of the melting theory of cubic perovskite are applied to two perovskites MgSiO3 and CaSiO3 under extreme conditions of the Earth’s lower mantle. Our obtained melting curves of MgSiO3 up to 1400 GPa and CaSiO3 up to 136 GPa were compared with available experiment and other calculations and were in good agreement. The present study provides an effective theoretical tool for finding the melting curves of strongly anharmonic materials under extreme conditions. Our theoretical calculations would be helpful to clarify geological formation process at the Earth’s lower mantle.