Structure and thermodynamics of Fe55, Co55, and Ni55 clusters supported on a surface

We study the structure and thermodynamics of Fe-55, Co-55, and Ni-55 clusters supported on a surface. The metallic bonding is described by a Gupta potential, and the surface is modeled by an idealized smooth plane coupled to the cluster by a Lennard-Jones interaction, with a variable parameter to describe the strength of the cluster-surface interaction. Optimum (lowest-energy) structures are determined by regular quenches, and the caloric curve of the clusters is extracted via a microcanonical multihistogram fit as a function of the cluster-surface interaction strength. The optimum structures are icosahedral for the free clusters and go through a series of transformations as the cluster-surface interaction strengthens, becoming successively flatter. The melting temperatures of the cluster correspondingly go through a series of steps with each change in optimum structure, but with an average trend toward higher melting temperatures as the cluster-surface interaction increases.