ABSTRACT
So far our studies have followed the development of the wave function, certainly the most influential idea in quantum chemistry’s first half century. It seems safe to say that its importance will continue. However, an increasingly prominent position is being taken by methods that focus on the density. To effect a transition in this direction, we pause to consider an unusual way to represent the properties of an electron distribution, beginning with an emphasis on the interelectronic interaction rather than adding electron correlation as an afterthought. The central concept here is the ‘‘hole’’ surrounding each electron which can arise from the fundamental statistics of fermions or their mutual repulsion according to Coulomb’s law. If we define a spatial form for an electron in a field of one nucleus, such
as that given by the exact solution for He cation, we have a very clear idea of the probability of an electron to be located in the neighborhood of any point. When a second electron is added to the system, we are faced with the complications of electron correlation. We will introduce the pair probability distribution or correlation function as a means for discussion of this problem.
