, Volume 20, Issue 6, pp 407-414

A quantum mechanical study of the perovskite structure type of MgSiO3

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Abstract

The periodic ab-initio Hartree-Fock Self Consistent Field program CRYSTAL has been used to study the electronic structure and equation of state of MgSiO3 perovskite. Three space groups were considered: Pm3m (cubic; ideal untilted SiO6 octahedra), P4/mbm (tetragonal; the octahedra are allowed to deform along and rotate about the crystallographic c cell edge) and Pbnm (orthorhombic; octahedra are allowed to deform along and rotate about the three cell edges).

The calculated orthorhombic structure is the most stable, in agreement with experiment. The relative stability of the three structures and the effect of pressure on the SiO6 octahedra is interpreted in terms of bond population data and is mainly determined by the oxygen-oxygen repulsion.