Recursive calculation of dimensional expansions for two-electron atoms

Abstract
An efficient procedure is developed for calculating perturbation expansions in δ=1/D, the reciprocal of the Cartesian dimensionality of space, for the ground-state energy of two-electron atoms. The method uses recursion relations between moments of the coordinate operators. Results through tenth order are presented for the helium atom. The perturbation series is divergent but Padé summation gives accurate results.