Density functionals and van der Waals interactions at surfaces

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