An analytical expression for the equation of state and thermo-physical quantities of exponential-6 ( exp- 6) fluid are derived based on the Ross variational perturbation theory. The developed formalism is applied to N 2 fluid. Comparisons of theory and simulations for exp- 6 potential fluid are presented. The agreement of numerical results of pressure and internal energy with Monte Carlo (MC) simulations show that the theoretical model is satisfactory except where a few points from metastable ones appeared in literature. The expression has been applied to fluid nitrogen and the fitting to experimental data of fluid N 2 is surprisingly good. The predictions of pressure in the range of high temperature and high density are satisfactory. It has also been found that the analytic equation of state for exp- 6 potential fluid based on RDF proposed by Sun et al. is better in a wide range of pressures and temperatures than that derived from PY expression. Comparisons show that a potential dependence on temperature and density (or volume) may be necessary for the understanding of interaction between N 2 molecules. The equation of state can also be extended to application of important real gases such as H 2, O 2, CH 4, CO and CO 2.
Large-D expansion from variational perturbation theory
