Configuration-interaction approach for high-lying singly and doubly excited states of two-electron systems - art. no. 040502

We introduce a configuration-interaction expansion in terms of Sturmian fun ctions, which provides very accurate nonrelativistic energies for the high- lying singly and doubly excited states of a two-electron system. The approa ch, which requires a substantially smaller basis size by contrast to the st andard configuration interaction methods, provides accurate results even fo r large total angular momenta. Key features are the use of different number s of Sturmian functions for each electron, the inclusion of many different pairs of nonlinear parameters in the expansion, as well as complex scaling. The accuracy and convergence of the method, applied to helium, increases w ith the degree of excitation of one of the two electrons.