Equations of state for wide ranges in pressure and temperature

It has been shown recently (Holzapfel et al 2001 J. Phys. Chem. Ref Data 30 515-29) that equations of state (EOS) data for simple metals like Cu, Ag and Au can be described most accurately on the base of a modified Mie-Gruneisen model including intrinsic anharmonicities. In contrast to commonly applied parametric EOS forms, which use only temperature dependent parameters, V (T), K (T) and K' (T), in the same parametric form, the present approach describes the thermal pressure more accurately and allows therefore to extrapolate more safely into wider ranges of pressure and temperature. Starting from the phonon density of state and a separate modelling of zero temperature and thermal contributions including quasiharmonic and intrinsically anharmonic contributions, the low energy part of the phonon density of states is represented by a modified pseudo-Debye model, which needs only one additional Einstein frequency for the high energy part. This optimised model is successfully applied to describe not only the EOS of Cu, Ag and Au, but also of other simple solids like NaCl and MgO, which are of special interest for pressure measurements in wide ranges of pressure and temperature.