PSEUDOPOTENTIAL PERIODIC HARTREE-FOCK STUDY OF MG2SIO4 POLYMORPHS - OLIVINE, MODIFIED SPINEL AND SPINEL

Pseudopotential periodic Hartree-Fock calculations have been performed on the three polymorphs of Mg2SiO4 with a polarized split valence bas is set. The energy differences between polymorphs at their experimenta l geometries are correctly predicted. The olivine to modified spinel a nd olivine to spinel phase transition pressures have been estimated an d agree within a few GPa with their experimental values. The bonding i n Mg2SiO4 is discussed from the point of view of the, band structures, projected density of states, electron density and electron localizati on function (ELF) curves. It is concluded that both Mg-O and Si-O bond s are highly ionic.