An accurate van der Waals-type equation of state for the Lennard-Jones fluid

A new equation of state (EOS) is proposed for the Helmholtz energy F of the Lennard-Jones fluid which represents the thermodynamic properties over a wide range of temperatures and densities. The EOS is written in the form of a generalized van der Waals equation, F=F-H+F-A, where F-H is a hard body contribution and F-A an attractive dispersion force contribution. The expression for F-H is closely related to the hybrid Barker-Henderson pertubation theory. The construction of F-A is accomplished with the Setzmann-Wagner optimization procedure on the basis of virial coefficients and critically assessed computer simulation data. A comparison with the EOS of Johnson et al. shows improvement in the description of the vapor-liquid coexistence properties, the p upsilon T data, and in peculiar, of the caloric properties. A comparison with the EOS of Kolafa and Nezbeda which appeared after the bulk of this work was finished shows still an improvement in the standard deviations of the pressure and internal energy by about 30%.