First-Principles Study of Orthorhombic Perovskites MgSiO₃ up to 120GPa and Its Geophysical Implications

High-pressure behaviour of orthorhombic MgSiO₃ perovskite crystal is simulated by using the density functional theory and plane-wave pseudopotentials approach up to 120GPa pressure at zero temperature. The lattice constants and mass density of the MgSiO₃ crystal as functions of pressure are computed, and the corresponding bulk modulus and bulk velocity are evaluated. Our theoretical results agree well with the high-pressure experimental data. A thermodynamic method is introduced to correct the temperature effect on the 0-K first-principles results of bulk wave velocity, bulk modulus and mass density in lower mantle P/T range. Taking into account the temperature corrections, the corrected mass density, bulk modulus and bulk wave velocity of MgSiO₃-perovskite are estimated from the first-principles results to be 2%, 4%, and 1% lower than the preliminary reference Earth model (PREM) profile, respectively, supporting the possibility of a pure perovskite lower mantle model.