; EN   R function. The significant contribution to the theory on the role of atoms in chemical reactivity has been elaborated by with the goal to: "understand the subtle interplay between the geometrical and/or electronic degrees of freedom of both isolated molecules and the reactive systems". The coupling has been described in the atomic discretization at the CSA level, originally proposed by Nalewajski. This sophisticated approach has been founded on the electron preceding perspective ("chemical thinking") and had of-necessity combined the basic parameters from two non-equivalent sources: the exact positions of nuclei and exact forces thereon have been used parallelly to the populations of the point-atoms, reasonably calculated (albeit arbitrarily defined) from the equalization of the chemical potential in the system. The lasting value of this analysis was in formulating the geometrical minimum energy coordinate (MEC) concept for tracing the changes in electronic structure of a reacting system.