Abstract
The derivation of the first nonadiabatic correction in a model potential for one or more electrons outside a spherically symmetric core is considered. Previous derivations of this term employed an additional appeal to perturbation theory. It is shown that this is not an essential restriction. Earlier conclusions that no three-body (two electrons plus core) term of this type exists are confirmed. An alternative derivation of this term, with the same conclusion, is sketched. The question of the appropriate normalization of the eigenfunctions of the model Schrödinger equation is also addressed.

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