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Equation of state, elastic properties, and stability of CaSiO 3 perovskite: First principles (periodic Hartree‐Fock) results

1993; American Geophysical Union; Volume: 98; Issue: B11 Linguagem: Inglês

10.1029/93jb02175

2156-2202

David Μ. Sherman,

X-ray Diffraction in Crystallography

The cubic CaSiO 3 perovskite phase is possibly the third most abundant mineral in the lower mantle. In addition to its geochemical significance, CaSiO 3 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 CaSiO 3 perovskite are calculated using the periodic Hartree‐Fock formalism. Cubic CaSiO 3 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 CaSiO 3 in close agreement with experiment ( V 0 = 44.96 Å 3 , K 0 = 300 GPa, and K 0 ′ = 4). The aggregate shear modulus of CaSiO 3 perovskite is found to be 209 GPa which is comparable to that of MgSiO 3 perovskite. The high seismic velocities of CaSiO 3 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 CaSiO 3 perovskite is stable relative to the free oxides at pressures up to 130 GPa (the core‐mantle boundary).