Electron pair correlation energies for ZN2+

Pair energies contributing to the correlation energies of the outer‐shell electrons (n = 3) as well as for the 1s2 and 2s2 pairs are computed for the Zn2+ closed‐shell ion by means of the variational‐perturbation method starting with the sum of one‐electron Hartree–Fock operators as the zeroth‐order Hamiltonian. The results allow an understanding of the electron correlation for pairs of electrons of the p and d type. For 3p3d pairs it has been found that the correlation energy for the singlet pair of 1D symmetry is lower than for the triplet pair 3D. The 3l‐3l′ correlation energies are compared with the MBPT results of Kelly and Ron for Fe. The total correlation energy of the outer shell is −1.032 a. u.