Weak Interactions

Non-covalent interactions dominate soft matter, and have been particularly difficult to model theoretically. Given their importance in supramolecular chemistrySupramolecular chemistry, be it in biomolecular problems or in crystal engineering, much effort has been devoted to visualize them in real space. In this Chapter, we will review several scalar fieldsFieldscalar devised to bridge this gap, paying particular attention to the Non-Covalent Interactions index (NCI). More specifically, we will review the relationship of NCINon covalent interaction index (NCI) to the bosonic kinetic energy density, its ability to recover electron localization as well as weak interactionsWeak interactions (even beyond QTAIMQuantum Theory of Atoms In Molecules (QTAIM) features). We will show some examples where the use of NCI is specially advised and we will introduce the tools for a more detailed NCINon covalent interaction index (NCI) analysis (integrals, bifurcation points, etc.). We will finish the chapter with some other existing tools for weak interactionsWeak interactions and their mutual relationship.