APPLICATION OF INTEGRAL-EQUATION THEORIES TO THE NITROGEN MOLECULE

The Percus-Yevick (PY) and the hypernetted chain (HNC) integral equati ons have been applied to realistic, non-spherical, intermolecular pote ntials for nitrogen. Non-additive contributions, in the form of the Ax ilrod-Teller three-body interaction, have been considered. The integra l equations were solved after expansion in spherical harmonics and the solution procedure is described in detail. Thermodynamic properties o f the gas calculated through the compressibility and the virial routes are in surprisingly good agreement with experimental data. Typical de viations are within +/-0.2 per cent for both p rho T and sound-speed d ata at sub-critical densities. Some improvement may be achieved by fit ting the three-body dispersion coefficient. We conclude that a simple integral-equation theory and a reasonably sophisticated anisotropic pa ir potential, coupled with the Axilrod-Teller three-body term, can off er a good description of the thermodynamic surface at sub-critical den sities. A closure more accurate than either PY or HNC will be required if good results are to be obtained at densities above the critical. ( C) 1996 American Institute of Physics.