Perturbation theory for the Lennard-Jones diatomic fluid. I. Site-centered spherical harmonic coefficients

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Abstract
The RAM perturbation theory is tested via calculations of spherical harmonic coefficients Gklm of the site–site pair correlation function G(12) for Lennard-Jones diatomic fluids at a range of elongations and state conditions. The accuracy ranges from good to excellent, depending upon the particular form of implementation of the theory. Although not a necessary prerequisite, the accuracy of the theory may be improved when exact values of the average site–site pair correlation function are used as input quantities in the calculations. This permits comparison with a set of alternative theories which require such input information, and which are based on the site-superposition approximation (SSA). In addition to the intrinsic advantage of possessing the ability of compute the full G(12), the accuracy of the RAM results appears always to be equal to or better than that of the SSA theories.