Comparative ab initio study of lattice dynamics and thermodynamics of Fe2SiO4- and Mg2SiO4-spinels

Lattice dynamics and thermodynamic properties of antiferromagnetic Fe2SiO4-spinel have been studied using density functional theory. Phonon dispersions are obtained for several hydrostatic pressures up to 20 GPa. They are used to calculate thermodynamic properties within the quasiharmonic approximation. Comparison with ab initio results obtained for Mg2SiO4-spinel is made in order to study the effect of the cation exchange on the dynamic and thermodynamic properties of (Mg, Fe)2SiO4-spinel. The obtained results have been compared with the available experimental data.