Ab initio calculations for structure and temperature effects on the polarizabilities of Nan (n≤20) clusters

We present a rigorous, nb initio theoretical calculation of the dependence of Na cluster polarizability on cluster size, up to 20 atoms, obtained by combining ab initio pseudopotentials with a gradient-corrected density functional. Using molecular dynamics, we find that for clusters as small as nine atoms, a multitude of degenerate isomers exists even at T=0. By calculating the polarizability of these isomers, we reproduce the generally decreasing nature of the measured polarizability curve, as well as its dips at "magic" numbers corresponding to closed electronic shells. Moreover, we find that the effect of a finite temperature on the cluster structure suffices to account for most of the quantitative discrepancy between theory and experiment.