We present an ab initio study of the thermoelastic properties of MgO over a wide range of pressure and temperature. Phonon dispersions for equilibrium and strained configurations are obtained from density-functional perturbation theory. They are used to calculate thermodynamical potentials within the quasiharmonic approximation and several derived quantities of physical interest without further approximations. These include the temperature dependence of individual elastic constants at high pressures. Extensive and successful comparisons with experimental data demonstrate that the quasiharmonic approximation combined with ab initio phonon calculations provides an important theoretical approach for exploring thermodynamical properties of materials over a considerable pressure-temperature regime.

• Received 14 October 1999

DOI:https://doi.org/10.1103/PhysRevB.61.8793