Generalizing segregation and chemical ordering in bimetallic nanoclusters through atomistic view points

We predict general trends for surface segregation in binary metal clusters based on the difference between the atomic properties of the constituent elements. The energetically most favorable site for a guest atom on a pure metal cluster is determined considering the attractive and repulsive contributions of the cohesive energy of an atom in the cluster. It is predicted that for adjacent elements in a period of the periodic table, the bimetallic system would be more stable if the component with smallest valence electron density is placed on the surface. On the other hand, in bimetallic clusters built with elements of only one group, the trend to be in the volume (of the atomic component with smaller core density) will be higher for that cluster with atomic components most separated in the group. Such chemical ordering trends in the lowest energy configurations of Pt-Au, Pt-Pd, and Pt-Ni binary alloy clusters are verified for their 561 atom systems through a simulated annealing process. Some of our atomistic predictions are verified through quantum mechanical calculations.