Investigating the metallic behavior of Na clusters using site-specific polarizabilities

A site-specific analysis scheme based on density functional theory is used to investigate the static polarizability response of NaN clusters for N up to 80. The cluster structures used in the study stem from extensive searches for the respective global minima. The analysis involves partitioning the total cluster polarizability exactly into site (or atomic) contributions; it also results in the decomposition of the polarizability into local (or dipole) and charge transfer contributions. The computed total polarizabilities are found to be in excellent agreement with recent experimental measurements up to a small overall shift. The site analysis provides clear evidence that interior atoms in sodium clusters are strongly screened from an applied external field by the charge induced at the cluster surface. In addition, cluster size trends in the local and charge transfer contributions are shown to be reproduced very well by a simple metal sphere model. The overall picture is that of clusters exhibiting metallic behavior down to the smallest sizes.