Parametrization of perovskite structures:: an ab initio study

An overview of the pressure, temperature and chemical composition dependence of the lattice distortion in orthorhombic ABO perovskite structures is presented. Within the framework of the so-called global parametrization method (GPM) [Thomas (1998). Acta Cryst. B54, 585-599] an improved description for the position of the A cation in terms of the AO(12) and BO6 polyhedral volume ratio is proposed. The relationship is derived from an extensive ab initio study based on the density functional theory. The applicability of the improved GPM in combination with ab initio total energy calculations in the prediction of changes in the structural distortion under increasing hydrostatic pressure is investigated. Test calculations are performed for the geophysically important magnesium silicate perovskite and the results are compared with the available theoretical and experimental data.