AN AB-INITIO PERTURBED ION STUDY OF PYROPE GARNET STRUCTURE

An ab initio perturbed ion (aiPI) study has been carried out for magne sium-aluminium silicate garnet, Mg3Al2Si3O12 (pyrope). Slater type orb itals for representing atomic centres and large clusters ranging from 148 to 188 atoms have been used. Geometry optimizations have been perf ormed with the aim of determining the lattice energy, lattice paramete rs and bulk modulus, as well as the force constants and vibrational fr equencies of radial displacements associated with the local relaxation of this structure. Numerical results are analysed and compared with e xperimental 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 characterizati on of the local properties of complex ionic systems.