One-Dimensional Model for Exchange Forces

Abstract
Four different types of perturbation theories for the exchange forces between two atoms are applied to the lowest gerade and ungerade state of a simple one‐dimensional model. It is shown that the second‐order energy in one of the expansions (the Eisenschitz–London, van der Avoird, or Hirschfelder HAV expansion) exhibits undesirable behavior in the limit corresponding to large internuclear distances.