Second-order electron correlation energies for some 3d1 and 3d14s2 ions

Second-order correlation energies for the ground states of Cu−, Ge2+, Kr6+ (3d104s2 configuration) and Cu+ and Kr8+ (3d10 configuration) are calculated within the framework of the variational-perturbation formulation of the Rayleigh–Schrödinger Hartree–Fock perturbation theory. The method is based on the application of symmetry-adapted pair functions taken in the form of partial-wave (PW) expansions. M- and N-intrashell as well as LM- and MN-intershell correlation effects were considered. Special attention is paid to the determination of the Z-dependence of both the PW increments to the pair energies and the second-order pair energies, which represent (for the M and LM shells) very close approximations to the ‘‘all external’’ pair correlation energies. It is found that the PW increments change in a highly regular way according to the rules previously found for the K- and L-shell electrons of the Ne-isoelectronic sequence. All pair energies calculated in this work disclose a monotone Z dependence, which is not the case for the Ne-like systems. Some attention is paid to the impact of the 4s2 electrons on the correlation energies for the M shell, which turned out to be very small.