Time-dependent density-functional-theory calculation of the van der Waals coefficientC6of alkali-metal atoms Li, Na, K; alkali-metal dimersLi2,Na2,K2; sodium clustersNan; and fullereneC60

Abstract

We have employed time-dependent density-functional theory (TDDFT) to calculate the long-range dipole-dipole dispersion coefficient (van der Waals coefficient) ${C}_{6}$ of alkali-metal atoms Li, Na, K; alkali-metal atom dimers ${\mathrm{Li}}_{2}$, ${\mathrm{Na}}_{2}$, ${\mathrm{K}}_{2}$; sodium clusters containing even number of atoms ranging from 2 to 20 atoms; and fullerene ${\text{C}}_{60}$. The dispersion coefficient is obtained via Casimir-Polder expression which relates it to the frequency dependent linear polarizability at imaginary frequencies. The frequency-dependent polarizabilities are calculated by employing TDDFT-based complete sum-over-states expressions for the atoms, and direct TDDFT linear response theory for the closed shell dimers and clusters.