Perturbation theory for the thermodynamic properties of liquid nitrogen using model potentials

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Abstract
A statistical mechanical perturbation theory due to Fischer has been used to calculate thermodynamic properties of liquid nitrogen for model intermolecular potentials due to Cheung and Powles (CP), Raich and Gillis (RG), and Berns and van der Avoird (BV). Refinements in the numerical implementation of the Fischer theory are described. Results for the CP potential agree well with both simulation and experimental data except at high density and high temperature. Differences between theory and experiment are usually comparable to the differences between two sets of experimental data for the CP potential but are generally larger for the other two potentials. For both BV and RG potentials the excess Helmholtz energies and excess internal energies are up to 15 and 10 per cent higher, respectively, than experimental values whereas the predicted pressures are low by 100–200 bar for RG and 50–100 bar for BV. The BV potential is slightly more satisfactory than the RG potential overall. Results for spherical harmonic components of the radial correlation function for the CP potential calculated using zeroth and first order approximations in the Fischer theory and also in the RAM theory are also compared with results from molecular dynamics simulations.