Elastic Properties of CaSiO3 Perovskite from ab initio Molecular Dynamics

Abstract

Ab initio molecular dynamics simulations were performed to investigate the elasticity of cubic CaSiO 3 perovskite at high pressure and temperature. All three independent elastic constants for cubic CaSiO 3 perovskite, C 11 , C 12 , and C 44 , were calculated from the computation of stress generated by small strains. The elastic constants were used to estimate the moduli and seismic wave velocities at the high pressure and high temperature characteristic of the Earth's interior. The dependence of temperature for sound wave velocities decreased as the pressure increased. There was little difference between the estimated compressional sound wave velocity (V P ) in cubic CaSiO 3 perovskite and that in the Earth's mantle, determined by seismological data. By contrast, a significant difference between the estimated shear sound wave velocity (V S ) and that in the Earth's mantle was confirmed. The elastic properties of cubic CaSiO 3 perovskite cannot explain the properties of the Earth's lower mantle, indicating that the cubic CaSiO 3 perovskite phase is a minor mineral in the Earth's lower mantle.

Elastic Characterization of S- and P-Wave Velocities in Marinelike Silica: The Role of Nonequilibrium Molecular Dynamics

“…For isotropic systems, such velocities are directly related to the bulk and shear modulus. Examples can be found in the literature where ab initio molecular dynamics simulations were performed in order to calculate the shear and bulk modulus of a given material and then simply compute the isotropically averaged sound velocities. , For nonisotropic systems as α-quartz, the relationship between the elastic properties of the material and the seismic wave velocities becomes more complicated: the Christoffel equation allows the calculation of wave velocities in different directions from the elastic stiffness tensor components. Several examples of the application of this equation can be found in the literature, where equilibrium MD techniques were employed. − …”