A full implementation of the response iteration scheme for density functional calculations.

We describe the implementation of the response algorithm for solving the Kohn-Sham equations and equations of similar structure that appear frequently in calculations of the structure of inhomogeneous many-body systems. The algorithm solves directly for the (spin) density. We have implemented the method for arbitrary geometries in a way that does not need the explicit calculation of unoccupied states. We apply the method to the two sample molecules C6H6 and C60, as well as to the metal clusters Mg30 and Na40. Starting from very rough guesses for the initial electron density, convergence is reached significantly faster than with previous update algorithms.

Van der Waals interactions: accuracy of pair potential approximations.

Van der Waals interactions between single atoms and solids are discussed for the regime of large separation. A commonly employed approximation is to evaluate this interaction as a sum of two-body interactions between the adatom and the constituent atoms of the solid. The resulting potentials are here compared with known results in various geometries. Analogous comparisons are made for diatomic molecules near either single atoms or semi-infinite surfaces and for triatomic molecules' interactions with single atoms.