Structural properties of bimetallic clusters from density functional calculations

The structural properties and energy ordering of the lowest lying isomers of bimetallic (CuAu)(n) and (PtPd)(n), n=5-22 clusters have been investigated by means of density functional theory (DFT) in the generalized gradient approximation (GGA). The initial cluster geometry optimization is performed by using a genetic algorithm with the many body Gupta potential. This technique provide a distribution of the lowest energy cluster structures, that are further reoptimized using the DFT-GGA methodology. The energy ordering of isomers obtained with the Gupta potential does not agree, in general, with the one obtained using DFT-GGA for the two bimetallic clusters investigated. However, the lowest energy strucutures of the (CuAu)(n) nanoalloy show icosahedral patterns in agreement with the results obtained with the model potential. For the (PtPd). clusters segregation effects are found, where the Pt atoms are forming the cluster core and the Pd atoms are on the cluster surface, in agreement with previous calculations using the many body Gupta potential.