Moller-Plesset Perturbation Theory for Van der Waals Complexes Bound by Electron Correlation Effects: Ground States of the Ar and Mg Dimers

摘要

We demonstrate that MPPT through fourth order is suitable for studying van der Waals correlation-bound complexes provided that (a) accurate calculations are carried at the SCF level; (b) efficient basis sets for intersystem correlation effects (i.e., dispersion) are used; and (C) the full counterpoise (CP) method is applied to correct for basis set superposition error (BSSE). Interaction potentials are obtained for Argon and Magnesium with extended basis sets that contained up through the f-symmetry functions. For Ar2 the potential is characterized by Re approx. 7.3 ao and De approx. 0.34 mhartree and for Mg2 by Re approx. 7.4ao and De approx. 2.1 mhartree. The discrepancies between our potentials and the most accurate semiempirical and experimental results (Ar2:Re approx. 7.1ao, De approx. 0.45 mhartree; Mg2:Re approx. 7.35ao, De approx.1.93 mhartree, are analyzed in detail and attributed to the lack of higher than f-symmetry functions, as well as, in the Mg2 case, to the approximate nature of the MP4 approach. Reprints. (MJM)