Correlation functions of classical fluids. II. The direct correlation functions of mixtures of Kihara molecules in the Percushyphen;Yevick theory and the integral compressibility equation of state

摘要

We have determined the direct correlation functionsCij(r) for binary mixtures from the Percushyphen;Yevick integral equation assuming the Kihara potential. The variations ofCij(r) with temperature, density, and composition are examined. The characteristics of the correlations functions are found to be complex functions of the thermodynamic state that obey no simple rules. For most part, the theoretical results are confirmed by experimental information. The resultingCij(r) are used in an ``integral'' compressibility equation of state, newly proposed by Baxter, for mixtures to produce thePhyphen;Vhyphen;Tinformation on the argonhyphen;nitrogen system. Comparison with the virial equation of state and experiments shows that the predictions from Baxter's formula are superior at low densities, while the virial pressures are better at high densities. We also investigated the direct correlation functions of some pure substances, including argon, krypton, and xenon. For the case of argon, the use of a numerical potential advanced by Dymond and Alder proves to sustain a better comparison with experimental xhyphen;ray diffraction data.