Configurational transitions in processes involving metal clusters

We define the configurational state of an atomic system, e.g. a cluster of metal atoms, in terms of the nuclear coordinates of a specific local minimum of the potential energy surface (PES). Three types of configurational transitions are reviewed: chemical reactions, phase transitions in clusters and catalytic chemical processes involving clusters as catalysts. The analysis of the first two cases shows that although vibrational degrees of freedom of nuclei and configurational degrees of freedom are separable in lowest order, thermal motion of nuclei nevertheless influences the rate of a configurational transition. Therefore the height of the barrier that separates configurational states of the transition for the PES differs from the effective activation energy for this transition. For example, ignoring the thermal motion of atoms in Lennard-Jones clusters leads to a predicted value of their melting points twice which accounts for the thermal motion of atoms. Hence, in determining parameters governing configurational transitions, evaluation of the PES parameters, say, within the framework of DFT (density functional theory) must be augmented by information from molecular dynamics or some other method that accounts for nuclear motion. sidering the configurational transitions, we are guided mostly by metal clusters and especially by gold clusters which have a variety of structures, whose optimal structures vary with cluster size. Because gold clusters exhibit small energy gaps between their ground and excited configurational states, they have catalytic properties in both free and bound states with bulk systems. We review and analyze studies of nanocatalysts composed of a metal oxide surface with small gold clusters attached. In particular, the analysis shows that DFT is able to determine the structure of a nanocatalyst, but is not suitable for analyzing the catalytic process because that process often involves multiple electronic states and nuclear motions, while the standard DFT works only within the framework of the PES of the ground electronic state at a fixed geometry.