Density functional study of vibrational and thermodynamic properties of ringwoodite

Phonon dispersions and vibrational density of states (VDoS) of Mg₂SiO₄ ringwoodite have been calculated by first principles as a function of pressure up to 30 GPa using density functional perturbation theory. The predicted zone center frequencies are in close correspondence with existing Raman and infrared experimental data. The pressure dependence of phonon frequencies is linear and agrees well with experiments. The calculated VDoS has then been used in conjunction with the quasi-harmonic approximation to compute the Helmholtz free energy and thermodynamic properties, most of which agree very well with experiments.