Intermolecular Interactions via Perturbation Theory: From Diatoms to Biomolecules

This article is devoted to the most recent, i.e. taking place within the last few years, theoretical developments in the field of intermolecular interactions. The most important advancement during this time period was the creation of a new version of symmetry-adapted perturbation theory (SAPT) which is based on the density-functional theory (DFT) description of monomers. This method, which will be described in Sect. 5.2, allows SAPT calculations to be performed for much larger molecules than before. In fact, many molecules of biological importance can now be investigated. Another important theoretical advancement was made in understanding the convergence properties of SAPT. It has been possible to investigate such properties on a realistic example of a Li atom interaction with an H atom. This is the simplest system for which the coupling of physical states to the unphysical, Pauli forbidden continuum causes the divergence of the conventional polarization expansion and of several variants of SAPT. This development will be described in some detail in Sects. 2–4, where, in addition to a review of published work, we shall present several original results on this subject. In an unrelated way, one of the most interesting recent applications of ab initio methods concerns the helium dimer and allows first-principle predictions for helium that are in many cases more accurate than experimental results. Therefore, theoretical input can be used to create new measurement standards. This broad range of systems that were the subject of theoretical investigations in recent years made us choose the title of the current review. With a few exceptions, the investigations of individual systems discussed here utilized SAPT. The calculations for helium are described in Sect. 6, recent wave-function based applications in Sect. 7, the performance of SAPT(DFT) on model systems in Sect. 8, and applications of SAPT(DFT) in Sect. 9. Section 10 summarizes work on biosystems.