Ab initiocalculations for structure and temperature effects on the polarizabilities ofNan(n<~20)clusters

Abstract

We present a rigorous, ab 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.