Structures of Au/Pt bimetallic clusters: homogeneous or segregated?

The question whether Au can alloy with Pt at the nano-scale size is still controversial. By performing density functional theory calculations for several small Au/Pt bimetallic clusters Au(m)Pt(n) (m + n = 4-6, 13), we find that, in all the most stable geometries, Pt atoms prefer to assemble together to form the core while Au atoms like to surround the Pt atoms to form the shell, and that evenly mixed clusters are structurally unstable. The unique geometric characteristics can be explained by analyzing the different electronic properties of Pt-Pt, Au-Pt and Au-Au bonds, and is expected also to apply to larger Au/Pt bimetallic clusters.