A perturbation treatment of the extended Hartree-Fock equations for 2s21S and 2p21S weakly quantized states of helium- like ions

Abstract

The first-order extended Hartree-Fock (EHF) equations for the 2s2 1S and 2p2 1S states of two-electron atomic systems are solved exactly. The solutions are used to evaluate the second-order EHF energies exactly and the third-order EHF energies with great accuracy. The EHF equations of these states correctly take into account the zero-order mixing of the wave functions and are comparable in accuracy to the conventional HF equations for non-degenerate states. The results of this paper are compared with those of experiment and of other calculations.