Density functionals and van der Waals interactions at surfaces

Recent progress in the construction of a density functional for van der Waals interactions is described, towards the background of successes of local and semi-local exchange-correlation density functional for dense matter. The functional should apply for atoms, molecules, surfaces, and other objects. The only input needed consists of the electron densities of the interacting fragments or surfaces, and their static polarizabilities or static image planes, respectively, which can be easily evaluated in a ground-state density-functional calculation. Results for well separated atoms, molecules, and atoms/molecules outside surfaces are in agreement with those of other, more elaborate, calculations. A description of the asymptotic van der Waals interaction between two parallel surfaces is also given.