Time-Dependent Density Functional Theory Calculation of van der Waals Coefficient of Potassium Clusters

We employ all-electron ab initio time-dependent density functional theory (DFT)-based method to calculate the long range dipole-dipole dispersion coefficient (van der Waals coefficient) C-6 of potassium atom clusters (K-n) containing even number of atoms, n ranging from 2 to 20. The dispersion coefficients are obtained via Casimir-Polder relation. The calculations are carried out with the asymptotically correct statistical average of orbital potential and compared with the results obtained using Vosko-Wilk-Nusair representation of exchange-correlation potential within local density approximation. We report the dispersion coefficients between clusters of sodium and potassium atoms as well. The present results have been compared with the available jellium-based model and other DFT results in the literature. We also study the relationship between volume of the cluster and the C-6 for K clusters. It is observed that the C-6 scales as square of the volume. (c) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109:1376-1384, 2009