AN AB-INITIO PERTURBED ION STUDY OF PYROPE GARNET STRUCTURE

An ab initio perturbed ion (aiPI) study has been carried out for magnesium-aluminium silicate garnet, Mg3Al2Si3O12 (pyrope). Slater type orbitals for representing atomic centres and large clusters ranging from 148 to 188 atoms have been used. Geometry optimizations have been performed with the aim of determining the lattice energy, lattice parameters and bulk modulus, as well as the force constants and vibrational frequencies of radial displacements associated with the local relaxation of this structure. Numerical results are analysed and compared with experimental data, the geometrical cell parameters obtained by computer simulation being similar to the experimental results. This comparison validates the aiPI methodology used in the theoretical characterization of the local properties of complex ionic systems.