Structures and Stabilities of Platinum-Gold Nanoclusters

A genetic algorithm, coupled with the empirical Gupta many-body potential, is used to perform global optimisations for Pt-Au bimetallic clusters, with 1:1 composition, over a broad size range (N = 2-100). By analyzing different stability criteria, such as binding energy (E-b) and second difference in energy (Delta E-2) the lowest energy structures, i.e., global minima (GM), were determined. Icosahedron-based structures predominate as GM in the small size regime (up to N = 28). For medium sized clusters, e.g., N = 38, a strong preference for FCC-type structures is found. Moreover, a previously predicted GM structure for N = 98, i.e., the Leary Tetrahedron (LT), was found as the GM for 98-atom Pt-Au clusters. Density Functional Theory (DFT) local geometry optimisations were also performed on smaller clusters (N = 2-20). Changes in cluster geometry were small, though relaxations in bond lengths were observed. At the Gupta potential level, it was found that PtcoreAushell segregation is energetically preferred, which was subsequently confirmed by our DFT calculations for selected nuclearities.