Role of electron correlation in determining the binding limit for two-electron atoms

Abstract

Using two trial wave functions for a nonlinear variational study, the ground state of the two-electron isoelectronic sequence has been investigated for a continuously variable electron-electron coupling constant $\lambda$. These calculations extend the analogous study of the preceding paper by including explicit angular correlation on the one hand, and extra orbital flexibility on the other hand. The results confirm the earlier conclusion that for sufficiently large positive $\lambda$ (corresponding to nuclear charge $Z<\mathrm{}1\mathrm{}$) the ground-state energy penetrates into the continuum as a localized "bound" state, before terminating at a branch-point singularity.