Valence electronic force and core electronic force. Significance of core electrons on chemical binding

Abstract

The roles of core electrons and valence electrons are analyzed in terms of force for the first row diatomic molecules Li 2–F 2. We employed a basis set for which the Hellmann–Feynman theorem effectively holds. In order to take nuclear repulsion into account, net core and valence forces as well as net orbital forces are defined and used for the analysis. At smaller internuclear distances, core electrons exert an attractive net force for all the molecules investigated. This is due to the outer polarization of core electrons. At larger internuclear distances, the net core force becomes more attractive as the number of valence electrons increases. The net valence force, on the other hand, becomes more repulsive although the trend is less clear than for the core force. These results, which are contrary to a chemical intuition, are interpreted by repulsion among the valence electrons and the subsequent core electron polarization.