THE DEVELOPMENT OF METALLIC BEHAVIOR IN CLUSTERS

A review is presented of theoretical models for describing and rationa lizing the development of metallic properties in clusters, as a functi on of cluster size. Clusters, which span a wide size range, can be app roached from the bulk solid (infinite cluster) limit-via quasi-continu um models derived from condensed matter physics-and from the small mol ecule limit-via discrete quantum mechanical models. Smooth and oscilla tory cluster size effects are described and their origins rationalized . The competition between electronic and geometric shell stability eff ects, and the importance of the cluster temperature and its physical s tate, are discussed. The archetypical metal to non-metal transition ob served in mercury clusters, as a function of size, is considered and t he possibility of forming metallic clusters from non-metallic elements is investigated.