Van Vleck Perturbation Theory Research Articles

Extended average energy perturbation calculation of the 2s 2 and 2p 21S resonance state energies of two-electron atoms

An extended average energy (EAE) calculation of the 2s 2 and 2p 2 1S resonance state energies of two-electron atoms is carried out. We take the bare-nucleus hamiltonian as the initial approximation and treat the zeroth-order degeneracy by van Vleck perturbation theory, For both H − and He the lower state energies agree quite well with experiment while the upper state is about 1–2 eV too high. Our remits for He are comparable in accuracy to those obtained by the 1/ Z Hartree—Fock perturbation method. A brief concluding discussion of ways to improve the simple EAE technique is presented.

Interchange Theorems in Degenerate Perturbation Theory

We derive the equivalent of Dalgarno's interchange theorems for the case of exact or near degeneracy using Van Vleck perturbation theory. The application to excited states and to calculations based on our “distinguishable electron” method is discussed.