A method is introduced that drastically simplifies modified configuration interaction (MCI) calculations involving several electrons. All the radial matrix elements in MCI or correlated calculations are formulated as products of simple, independent one-dimensional integrals: one from 0 to $\infty$, all the others from 0 to 1. The method is easily applicable to CI and to direct correlated calculations for more than two-electrons. Extremely high levels of numerical accuracy are obtained for the radial limit of the ground state of helium, far exceeding the best results in the literature.

• Received 1 October 1996

DOI:https://doi.org/10.1103/PhysRevLett.78.2325