First-principles determination of elastic properties of CaSiO3 perovskite at lower mantle pressures

Abstract

We investigate the equation of state and elasticity of cubic CaSiO3 perovskite up to 140 GPa using the plane wave pseudopotential method within the local density approximation. The calculated equation of state parameters of the cubic phase are in excellent agreement with those from recent quasi-hydrostatic compression data and from all-electron linearized augmented plane wave calculations. We determine the elastic constant tensor of the mineral from the calculated stress-strain relations. The bulk modulus of CaSiO3 perovskite is similar to that of MgSiO3 perovskite, however, its shear modulus is much higher at pressures corresponding to the lower mantle. This suggests that CaSiO3 perovskite can no longer be considered as an invisible component in modelling the composition of the lower mantle, and even small amounts of the mineral may affect significantly the seismic properties, particularly shear wave velocity, of the generally accepted Mg-rich silicate perovskite dominated composition of this region. Moreover, CaSiO3 perovskite exhibits strong anisotropy (about 30 % shear-wave polarization anisotropy) at pressures corresponding to the transition zone and the top of the lower mantle.