Equation of state, elastic properties, and stability of CaSiO3 perovskite: First principles (periodic Hartree‐Fock) results

Abstract

The cubic CaSiO3 perovskite phase is possibly the third most abundant mineral in the lower mantle. In addition to its geochemical significance, CaSiO3 perovskite provides a useful system with which to test the application of quantum chemistry to mantle silicates. Here, the electronic structure, equation of state, and elastic properties of cubic CaSiO3 perovskite are calculated using the periodic Hartree‐Fock formalism. Cubic CaSiO3 is found to be stable relative to an orthorhombic structure to at least 106 GPa. Calculations using a moderately extended basis set give an equation of state for CaSiO3 in close agreement with experiment (V0 = 44.96 Å3, K0 = 300 GPa, and K0′ = 4). The aggregate shear modulus of CaSiO3 perovskite is found to be 209 GPa which is comparable to that of MgSiO3 perovskite. The high seismic velocities of CaSiO3 perovskite means it will act as a seismic complement to magnesiowustite in the lower mantle. The free energy, as a function of pressure, of stishovite and B2‐CaO have also been calculated at the same level of theory. From those results, it is found that cubic CaSiO3 perovskite is stable relative to the free oxides at pressures up to 130 GPa (the core‐mantle boundary).