Physical Basis of Intermolecular Interactions

Many studies in chemistry and physics require accurate but easily computed descriptions of the energies of noncovalent interactions between molecules or parts of the same molecule. Examples include the simulation of gases and condensed phases of molecular materials, the prediction of their structures and properties, and the investigation of paths in configuration space (paths through the energy landscape), for example, in the study of protein folding. Such descriptions are best constructed with a sound understanding of the physical nature of the noncovalent interactions, and perturbation theory, in particular symmetry-adapted perturbation theory, provides a framework both for that understanding and for the construction of accurate analytical potential functions. The main terms that arise in that approach are the electrostatic and exchange-repulsion terms from first order in perturbation theory, and the induction and dispersion terms from second order. They will be discussed in turn in this review and illustrated with a few examples.