In this exclusive chapter, we present a brief overview of the quantum theory
of atoms in molecule (QTAIM) proposed by R. F. W. Bader. This theory is based on
the topological analysis of the electron density and related parameters. One of the
strengths of this theory is the accurate prediction, characterization, and quantification
of various interactions, including H-bond and van der Waals interactions. Herein, we
discuss the important aspects of QTAIM regarding the intra- and intermolecular
interactions in biologically active molecules discussed in the preceding chapters.
Within the framework of the QTAIM, I mention the criteria of H-bonds and
characterize the various H-bonds on the basis of topological parameters, and continue
to quantify the strength of the H-bond. I will also describe a very user-friendly software
AIMAll to perform the QTAIM analysis and explain the obtained results. In order to
provide the contents digestive, I will include examples of molecules from Chapters 3,
4, and 5. I believe that this chapter will guide the readers interested in various kinds of
interactions in biologically active molecules.
Keywords: AIM, AIMAll, BCP, Bond strength, BSSE, Characterization,
Complex, Counterpoise, Dimer, Electron density, H-bond, Intermolecular
interaction, Intramolecular interaction, Laplacian, Molecular graph, QTAIM,
RCP, Reactivity, Stabilization, Supermolecular approach, Topology.