Intrinsic anharmonicity in equations of state and thermodynamics of solids

Using thermodynamic perturbation theory, we derive a simple formalism for treating intrinsic anharmonic effects in solids. In this formalism, the central quantity is the intrinsic anharmonicity parameter a , which can be derived from vibrational spectroscopy or computer simulation. Advantages of our approach include (1) correct low- and high-temperature behaviour, (2) analyticity of all the thermodynamic functions and (3) the possibility of systematic incorporation of higher-order anharmonic effects. This approach can be used in studying equations of state and thermodynamics of solids in a wide temperature range. A detailed comparison with other approaches is given.