PREDICTION OF THERMODYNAMIC PROPERTIES FOR FLUID NITROGEN WITH MOLECULAR-DYNAMICS SIMULATIONS

Molecular dynamics simulation results in the isochoric-isothermal ense mble are reported for a two-center Lennard-Jones model of fluid nitrog en characterized by the fixed molecular elongation L = 1/phi = 0.3292. New values of epsilon and sigma were determined by fitting the vapor pressure and the saturated liquid density of the model to experimental data at 94.67 K. The required vapor-liquid equilibrium data of the mo del were taken from a study using the NpT + test particle method. The resulting values are epsilon/k = 36.32013 K (36.673 K) and sigma = 0.3 2973 nm (0.33078 nm), with values in parentheses being those obtained previously from a Weeks Chandler-Andersen-type perturbation theory. Th en pressures and internal energies were calculated by molecular simula tions for 110 state points in the temperature range from 72 to 430 K a nd for densities up to 35 mol . L(-1). Comparison of the predictions b ased on the new parameters with the empirical equation of state of Jac obsen et al. shows good to excellent agreement except in the near-crit ical region. Moreover, for almost all state points the new parameters yield an improvement over old ones from perturbation theory.