Theoretical Approaches

Abstract

Different theoretical methods are presented in this chapter, starting from the description of ab initio methods, through their various approximations, to the description of other theoretical approaches that are often applied to characterize inter- and intramolecular interactions, especially hydrogen bonds. One can mention the Quantum Theory of Atoms in Molecules (QTAIM), various schemes of the decomposition of the energy of interaction, the Natural Bond Orbital (NBO) approach, the Electron Localization Function (ELF) method, the non-covalent interactions (NCI) approach and others. Parameters resulting from these methods are described, such as energetic and geometric ones; for example, binding energy, deformation energy, interaction energy or lengths of interatomic contacts. Other properties are defined and analysed: atomic charges, occupation of orbitals, orbital–orbital interactions, etc. Comparisons between properties of the hydrogen bond and other interactions described in the previous chapter are performed here.