Effects of intrinsic anharmonicity in the Mie–Grüneisen equation of state and higher order corrections

The usual quasiharmonic Mie–Grüneisen (MG) equation of state is modified by the inclusion of ‘intrinsic anharmonicities’, which have been considered up to now primarily in the high temperature limit. A comparison with experimental data for the rare gas solids, Ar, Kr and Xe and for MgO reveals that the anharmonic contributions cannot be represented perfectly within the MG approximation. A small but significant modification of the MG approach is presented to estimate intrinsic anharmonic contributions within a mean-field approximation for the thermal part of the internal energy. This estimate results in reasonable interpolations to low temperatures, where quantum effects are dominant. The present approach is also compared with more restricted recent theoretical results.