Theory of intermolecular forces. I. On the inadequacy of the usual Rayleigh‐Schrödinger perturbation method for the treatment of intermolecular forces

The problem of intermolecular interaction is examined by using spatial wave functions and the theory of permutation groups. In the special case of interacting 2‐electron systems it is proven that the Rayleigh–Schrödinger perturbation method, when starting from the ground state of the unperturbed system, could only give the physically inadmissible mathematical ground state of the complex (totally symmetric spatial eigenfunction). Then this property is considered in the case of arbitrary interacting systems and a general proof is proposed. From these results a general explanation of the inadequacy of the Rayleigh–Schrödinger expansion for the treatment of short range intermolecular interaction is proposed.