Low-temperature crystal structure of CaSiO3 perovskite : An ab initio total energy study

• The stability of cubic CaSiO3 perovskite with respect to octahedral rotations is investigated by ab initio total-energy calculations. The proposed theoretical ground-state crystal structure has the orthorhombic Pbnm symmetry. Pressure gradually reduces the average tilting of the SiO6 octahedra relative to the cubic axis, from 7degrees at zero pressure to 4degrees at about 150 GPa. The energy difference between the orthorhombic and cubic phases at 0 GPa is 63 meV per f.u. and shows weak pressure dependence. A possible stabilization of the cubic phase at finite temperatures by entropy effects is discussed.

Nyckelord

earths lower mantle

tin orbitals theory

lattice-dynamics

first-principles

elastic properties

mgsio3 perovskite

stability

state

equation

phase

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