EQUATION OF STATE, ELASTIC PROPERTIES, AND STABILITY OF CASIO3 PEROVSKITE - 1ST PRINCIPLES (PERIODIC HARTREE-FOCK) RESULTS

The cubic CaSiO3 perovskite phase is possibly the third most abundant mineral in the lower mantle. In addition to its geochemical significan ce, CaSiO3 Perovskite provides a useful system with which to test the application of quantum chemistry to mantle silicates. Here, the electr onic structure, equation of state, and elastic properties of cubic CaS iO3 perovskite are calculated using the periodic Hartree-Fock formalis m. Cubic CaSiO3 is found to be stable relative to an orthorhombic stru cture to at least 106 GPa. Calculations using a moderately extended ba sis set give an equation of state for CaSiO3 in close agreement with e xperiment (V0 = 44.96 angstrom3, K0 = 300 GPa, and K0' = 4). The aggre gate shear modulus of CaSiO3 perovskite is found to be 209 GPa which i s comparable to that of MgSiO3 perovskite. The high seismic velocities of CaSiO3 perovskite means it will act as a seismic complement to mag nesiowustite in the lower mantle. The free energy, as a function of pr essure, of stishovite and B2-CaO have also been calculated at the same level of theory. From those results, it is found that cubic CaSiO3 pe rovskite is stable relative to the free oxides at pressures up to 130 GPa (the core-mantle boundary).