Theoretical study of the intermolecular potential energy and second virial coefficient in the mixtures of CH4 and Kr gases: a comparison with experimental data

Abstract

The intermolecular potential energy surface (IPS) in the mixtures of CH4–Kr gases from ab initio calculations has been explored. The ab initio calculation was performed at the second-order Møller–Plesset perturbation theory (MP2), with the 6-311+G(2df,2pd) basis set, for three relative orientations of two CH4–Kr molecules as a function of CH4–Kr separation distance. In this work, the IPS, U(r), of the CH4–Kr complex has been investigated, where the vertex (V), edge (E) and face (F) of CH4 approaches to Kr have been considered. Then, adjustable parameters of the Lennard-Jones and Buckingham potential energy function are fitted to the ab initio MP2/6-311+G(2df,2pd) interaction energies for three different orientations. Assuming a given set of parameters, we theoretically obtained second virial coefficients for the CH4–Kr system, and compared with the experimental data at different temperatures. Trivial differences can be observed between the experimental and computational results.