The van der Waals (vdW) interaction is a long-range attraction between chemical species, arising from a correlation between instantaneous electronic charge fluctuations on each. It is present even when there is no chemical bond, and even when each species has no permanent multipole moment. The vdW interaction is much weaker in strength than a normal chemical bond, but it has important effects on the properties of materials. vdW interaction is ubiquitous in various kinds of materials. It is responsible for many phenomena such as sublimation of iodine, naphthalene, dry ice, and other organic molecules, high interlayer mobility of graphite, folding of long biomolecular chains such as DNA, RNA, and proteins, polymers, etc. Since computer calculations are more and more feasible, vdW has been a “hot area” in materials theory in the past decade. vdW effects can be captured by pairwise corrections, by nonlocal correlation functionals, and by approximations based on the random phase approximation (RPA). While pairwise models often deliver a satisfactory accuracy for chemistry, atom pair-potential models and the nonlocal vdW correlation energy functionals commonly miss many-body effects needed to describe fulleneres, nanotubes, metallic systems and molecular crystals. This lecture will explain: i) the background physics of vdW interaction, ii) the most common vdW approximations, and their applications.
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