Dispersion (Van Der Waals) Forces and TDDFT

Abstract

Abstract By “dispersion forces” [Mahanty 1976] we mean the part of the attractive van der Waals (vdW) interaction that cannot be attributed to any permanent electric multipoles. These ubiquitous forces are typically weaker than ionic and covalent bonding forces, but are of longer range than the latter, typically decaying algebraically rather than exponentially with separation. They are important in soft condensed matter and in rare-gas chemistry, for example. We will work in the electromagnetically non-retarded (non-Casimir [Milton 2001]) limit, which means in practice that we can treat interacting systems at separations from about a micron down to full overlap of electronic clouds. We do not aim for a complete review of vdW phenomena and theories, but will rather concentrate on adiabatic connection / fluctuation-dissipation (ACFD) approaches. These work with dynamic electron density-density response functions, which in turn can be calculated by TDDFT methods. An interesting alternative is suggested in Chap. 3.