A hard-core Exp-6 intermolecular potential function for determining virial coefficients of pure nonpolar and slightly-polar molecules

In this work, we have applied the hard-core term to the Exp-6 intermolecular potential function, in order to obtain a more realistic model for determining the values of second virial coefficients of nonpolar and slightly-polar gases. The second virial coefficients of 24 nonpolar and slightly-polar gases of quite differing natures, including hydrocarbons from the alkane, alkene, and aromatic families, as well as non-hydrocarbons such as carbon dioxide, were calculated using the proposed hard-core Exp-6 intermolecular potential function. The results showed that this integrated approach significantly improves the Exp-6 model, bringing it closer to reality. The average errors in calculated second virial coefficients, over the 564 data points considered, is just 1.5%. In addition, the third virial coefficients of non-polar or slightly-polar gases can be accurately predicted using this proposed potential function. For example, the AAD% of the predicted third virial coefficients of 327 data points corresponding to 11 gases by the proposed model is 50.5%, which is much smaller than the AAD% of the original Exp-6 (80.6%), Lennard-Jones (94.3%) and Kihara (73.5%) models.