A reliable semi-empirical approach for evaluating the isotropic intermolecular forces between closed-shell systems.

Abstract

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 (E _x) and coulomb (E _c) contributions. A semi-empirical approximation, which is a simple function of the first order coulomb energy (E _c ⁽¹⁾), is used to represent E _x. The representation for E _c is based on E _c ⁽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 E _x and influences the balance between E _x and E _c 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/R _m < ∞ where R _m is the interatomic or intermolecular distance corresponding to the van der Waals minimum.

Additional information

Notes on contributors

William J. Meath

Members of the Centre for Interdisciplinary Studies in Chemical Physics.

A.R. Allnatt

Members of the Centre for Interdisciplinary Studies in Chemical Physics.