The relationship between the molecular structure and the chemical properties: what about the topological analysis of the electron density distribution? An application to hydrogen bonds

Abstract

Molecular structure is determined by nuclei positions. From the Hellmann-Feynman theorem we know that the exact ground state electron density distribution ρ(r) depends on the nuclei positions only. Furthermore, the Hohenberg-Kohn theorem states that the total energy of a system can be written in terms of its ρ(r) distribution. In this context, the relationship between the structure of a molecular system and its physical and chemical properties should be reflected by the electron distribution. As far as the molecular structure is the straightforward consequence of interatomic interactions, a correspondence between these interactions and the observed ρ(r) applies. Accordingly, the interatomic interactions described in terms of ρ(r) can be considered as a fundamental subject of study to get insight on the structure-properties relationship, as the former is a conceptual bridge between the latter. The topological analysis of ρ(r) developed by Bader and co-workers [1] is a useful tool for characterizing atomic interactions in internuclear regions. It permits to obtain the molecular space partition into atomic basins that are separated by zero-flux surfaces S(r )o f the electron distribution and behave as quantum objects. Along the bond path directions ρ(r) is minimum at the surfaces S(r), where topological bond critical points rBCP appear and ρ(r) exhibits saddle distributions. Analysis of topological and energetic magnitudes of ρ(r )a trBCP permits a deep characterization of interactions. Following this description we have analyzed experimental and theoretically calculated energetic properties of hydrogen bonded systems in terms of the ρ(r) distribution at their rBCP’s [2-7].