Combination rules for intermolecular potential parameters. I. Rules based on approximations for the long‐range dispersion energy

Combination rules for intermolecular potential parameters based on different approximations for the long‐range dispersion energy are derived and applied to the Lennard‐Jones (12–6) and Kihara potential functions. The resulting group of rules is given by the expressions σ12 = <σ≳j, and e12 = <eσ6γ≳i/‖<σ≳6j<γ≳k ‖, where the i,j, and k subscripts may adopt the values a, g, or h indicating the type of mean (arithmetic, geometric, or harmonic, respectively) to be taken for the magnitude within the brackets. Expressions for γ depend on the approximation chosen for the van der Waals coefficient c6. This group of rules includes most of those previously proposed and others which are new. Experimental values of the interaction virial coefficient and unlike‐pair potential parameters obtained from viscosity data are used to test the validity of the rules. Six related rules are shown to be satisfactory for both potential functions and for accurate correlation of virial and viscosity data as well.

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