  We have carried out density functional theory based calculations of the size
dependent formation energy and geometry of Pt islands on Ru(0001), to model
Pt-Ru nanocatalysts which have been recently proposed as fuel cell anode. The
Pt islands are found to prefer two-dimensional structures. Furthermore, a
monotonic decrease in the formation energy per Pt atom suggests a propensity of
Pt atoms to wet the Ru(0001) surface. Calculated energy barriers for the
diffusion of Pt monomers and dimers on the facets and through the edges of a
superstructure modeling a Ru nanoparticle indicate that these edges help reduce
considerably the diffusion rates across them such that the Pt atoms prefer to
remain in the facet on which they were adsorbed originally and form 2D islands.
