Density functional study of structural properties of bimetallic Pt-Ni nanoparticles

A study has been made of the structures and energy ordering of the lowest-lying isomers of the bimetallic nanoparticles (PtNi$_{3})_{n}$, (Pt$_{3}$Ni)$_{n}$, and (PtNi)$_{n}$, with n=1-20. The lowest energy structures of binary Pt-Ni nanoclusters, modeled by the many-body Gupta potential, were obtained by using a genetic-symbiotic algorithm. These structures were further reoptimized within the DFT-GGA framework. The Gupta potential parameters used for the Pt-Ni interaction are the geometric average of the Pt-Pt and Ni-Ni ones. In agreement with the experimental evidence, segregation is observed in the Pt-Ni clusters, with the Ni atoms in the core and the Pt atoms on the cluster surface, even for the (PtNi$_{3})_{n}$ case. A discussion of segregation versus mixing effects will be presented.