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First principle calculation of elastic and thermodynamic properties of stishovite

Using ab initio plane-wave pseudo-potential density functional theory method, the elastic constants and band structures of stishovite were calculated. The calculated elastic constants under ambient conditions agree well with previous experimental and theoretical data. C13, C33, C44, and C66 increase nearly linearly with pressure while C11 and C12 show irregularly changes with pressure over 20 GPa. The shear modulus (C11-C12)/2 was observed to decrease drastically between 40 GPa and 50 GPa, indicating acoustic mode softening in consistency with the phase transition to CaCl2-type structure around 50 GPa. The calculated band structures show no obvious difference at 0 and 80 GPa, being consistent with the high incompressibility of stishovite. With a quasi-harmonic Debye model, thermodynamic properties of stishovite were also calculated and the results are in good agreement with available experimental data.