Second-order correlation energies of Mg and Ar

Abstract

An extensive variational-perturbation study of the second-order correlation energies of Mg and Ar is made to analyse the nature of various correlation effects. The variational-perturbation symmetry-adapted pair functions are taken in the form of partial-wave expansions. The results for the partial-wave energy increments, pair energies and total correlation energies are compared with related results. Special attention is paid to the M-intrashell and KM- and LM-intershell correlation effects. For the first time ab initio total correlation energies are obtained for atoms containing M-shell electrons. The results: E₂^Mg=-0.4279 and E₂^Ar=-0.7060 au agree very well with the estimates of the total correlation energies.