Simulation of Supported Metal Clusters

A metal cluster is an aggregate composed of metallic elements, ranging in size between a few and few thousand atoms, while larger entities are usually referred to as "particles." A metal cluster can exist in different forms: free, coated by a protective shell of ligands, or deposited on a support, in which the last case the expression "supported metal cluster" is employed. In these structures, nanoscale confinement effects appreciably modify the response properties of the metallic nanosystem. For example, the high surface/volume ratio assures that a great part of metal atoms lie at the surface in low-coordinated sites, which are therefore available for chemical sensing and catalysis. As another example, the collective oscillation of conduction band electrons which gives rise to plasmonic phenomena in bulk metals is modulated by the presence of metal/environment interfaces, thus producing the so-called surface plasmon resonances.Magnetic properties are also exalted by the reduction of the electronic density of states in such confined systems, hence producing enhanced magnetic moments and anisotropy, etc. All these properties are very sensitive not only to size, shape, and external fields but also - in the case of supported metal clusters - to the interaction of the cluster with the support. From the possibility of modifying the cluster properties by tuning cluster/substrate interactions, a great freedom in the physical and chemical behavior of these materials results and therefore their interest in science and technology. This interest has been translated into an intense theoretical effort aimed at the prediction and understanding of the structure and properties of metal clusters via simulations, which is the topic of the present entry.