Equation of state of fluid helium to very high pressure

Experimental speed-of-sound data up to 1 GPa and the variational perturbation theory of Ross were used to determine new parameters of the ‘‘exponential-six’’ interatomic effective pair potential of fluid helium. The potential was used in self-consistent integral equation calculations, based on a synthesis of the hypernetted chain and the mean spherical approximation, covering the fluid range of helium from 100 to 1000 K and up to the melting line (or up to 45 GPa). The calculated equation of state data in this range are in excellent agreement with all available experimental results. The calculated data from 1 GPa upward were correlated by a 16-coefficient modified Benedict–Webb–Rubin equation of state.