RELIABLE SEMIEMPIRICAL APPROACH FOR EVALUATING THE ISOTROPIC INTER-MOLECULAR FORCES BETWEEN CLOSED-SHELL SYSTEMS - APPLICATION TO THE HE-HE, NE-NE, AR-AR, KR-KR AND H2-H2 INTERACTIONS

A relatively simple tractable scheme for the evaluation of the isotropic intermolecular potential between two closed-shell systems, which contains one adjustable parameter, is proposed and tested using the He-He, Ne-Ne, Ar-Ar, Kr-Kr, and H2-H2 interactions as models. The approach is based on expressing the potential as a sum of exchange (Ex) and coulomb (Ec) contributions. A semi-empirical approximation, which is a simple function of the first order coulomb energy (Ec(1)). is used to represent Ex. The representation for Ec is based on Ec(1) and a suitably universally damped asymptotic expansion of the second-order coulomb energy through O(R-10). The adjustable parameter formally occurs in the representation for Ex and influences the balance between Ex and Ec in the representation of the potential. The results obtained for the model systems are in excellent agreement with reliable literature potentials, many of which contain several adjustable parameters, and suggest that the scheme proposed here is capable of yielding reliable potentials for 0.3≤R/Rm< <x> where Rm is the interatomic or intermolecular distance corresponding to the van der Waals minimum. © Taylor & Francis Group, LLC.