A floating one centre perturbation treatment for H-like molecules

Closed form one centre partial wave perturbation results are obtained through second order in the energy for H-like molecules with arbitrary nuclear charges. The expansion centre for the method is taken at an arbitrary point along the internuclear axis and the zeroth-order wave function is a screened “1s” function centred at the expansion point. Various fixed one centre calculations of other workers for the lsσ states of H and HeH⁺⁺ and for the 2pσ state of HeH⁺⁺ are generated as limiting cases of this more general treatment. The floating one centre perturbation results for the 1sσ states of H₂⁺ and HeH⁺⁺ are used as models for discussing the usefulness of allowing the expansion centre in the one centre method to be a function of nuclear configuration.