MICROSCOPIC CALCULATION OF THE VANDERWAALS INTERACTION BETWEEN SMALL METAL-CLUSTERS

The nonretarded van der Waals coefficicnts C6 and C-8 are determined for all pairs of neutral sodium microclusters with 1, 2, 8, 20, and 40 atoms. These small systems are described self-consistently within the jellium model and their multipole dynamical polarizabilities calculated making use of the time-dependent local density approximation. It is found that quantum size effects, in particular Landau fragmentation, play a crucial role in thc determination of the coefficients. Furthermore, it is found that the coefficients are very insensitive to the internal temperature of thc clusters, in the range of temperatures reachable experimentally. A discussion on the accuracy of the predicted values is given.