Interactions of platinum clusters with a graphite substrate.

Density functional theory calculations are used to elucidate the interactions of platinum clusters with graphite; the results are analyzed in terms of geometry, and energetic and electronic properties. Adsorption of platinum clusters from 1 to 38 atoms is evaluated on a 3-layer graphite model structure. The approach includes van der Waals interactions, which have proved to be essential to describe relatively weak interactions. The results show that when interacting with graphite, the clusters tend to slightly wetting the surface. Although the effect is more pronounced in the larger clusters investigated, the energy difference among total, partial, and non-wetting structures in small clusters is very low and may be easily overcome by thermal effects. The van der Waals energy contributes to enhance the graphite-cluster strength and is proportional to the number of interacting atoms at the interface. Small charge transfer takes place from the metallic cluster to the graphite surface and the cluster becomes polarized, with positive values at the interface, and negative values in the top. The interaction with graphite enhances the metallic character of the cluster as shown by density of states analyses. New states resulting from the interaction between graphite and the metal cluster may modify its catalytic behavior.