Key points are not available for this paper at this time.
The conditions on the behavior of a wavefunction for a system of charged particles near the coalescence of any two of them are derived. The new features of the derivation are: (a) the fixed-nucleus approximation is not required; (b) the wavefunction is not spherically averaged; (c) the wavefunction can have a node at the singularity; and (d) the consequences of the two particles being identical are examined. In addition to the general treatment, the electron—nucleus cusp conditions for diatomic molecules are discussed in detail.
Pack et al. (1966) studied this question.