Configuration-interaction Hartree-Fock calculations for two-electron atoms using a pseudopotential

We have developed an approach to study doubly excited Rydberg states of atoms or ions with two optically active electrons outside an ionic closed-shell core. The interaction between the core and one valence electron is modeled by an accurate semiempirical pseudopotential. For any given parity and total angular momentum, single configuration Hartree-Fock calculations are performed to build a basis set of numerical two-electron wave functions. Configuration-interaction calculations then provide the energy positions of the correlated states and their compositions in terms of the single configuration basis set. Atomic properties, such as autoionization linewidths, can be derived. Results concerning neutral barium are reported to illustrate the approach. They are compared with available experimental and theoretical data, and discussed. Energy positions of the bound and autoionizing $J=0$ even-parity and $J=1$ odd-parity states of barium below the 5d²D5/2 threshold are predicted as well as associated autoionization linewidths. The symmetrical ns² (n=7-11), 7p², and 6d² configurations are also studied. The overall agreement is satisfactory and especially good for high-lying doubly excited Rydberg states.