Dispersion coefficients for van der Waals complexes, including C-60-C-60

A previously proposed and tested [Phys. Rev. Lett. 76, 102 (1996), Phys. Re v Lett. 77 2029 (1996)] van der Waals density functional is applied to van der Waals complexes. Dynamic polarizabilities, alpha(iu), and dispersion co efficients, C-6, are obtained with a useful accuracy and at a low computati onal cost using ground-state electron densities as input. We compare result s for C-6 for small and medium-sized molecules with existing results obtain ed using more cumbersome methods. The computational simplicity of the funct ional opens up the possibility to treat large systems of real interest with in different fields of physics, chemistry and biology. This is illustrated by the application to C-60 We present results for the static polarizability alpha(0) and the dispersion coefficient C-6 for two such molecules.