Abstract
Let a many-electron Hartree-Fock radial function ΦHF(nl; r)=Πi=1N[PHF(nili; ri)] and the corresponding nonseparable variational function Φ(nl; r) be expanded in hydrogenic product functions ΦH(nl; r). The expansion coefficients Hnl|nl of Φ are O(Z1) for nn; they vanish when the sets n, n differ by more than two one-electron quantum numbers. It is shown that the expansion coefficients Hnl|HFn are O(Z2) when ν(n, n)=NΣi=1Nδ(nini)=2, i.e., when n and n differ in two places, and are O(Z1) when ν(n, n)=1. In the second case Hnl|HFnl=Hnl|nl+O(Z2); the Hartree-Fock and the nonseparable expansion coefficients coincide to first order. This result holds only if the one-electron Hartree-Fock functions PHF are not restricted by auxiliary conditions other than normalization. It does not hold, for example, if one requires the PHF to satisfy the orthogonality condition PHF(nl; r)P

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