Structure of pure metallic nanoclusters: Monte Carlo simulation and ab initio study

The structural stability and energetics for small copper and gold clusters Cu (n) and Au (n) (n = 21-56) were investigated using an effective Monte Carlo simulated annealing method, which employs the aggregate-volume-bias Monte Carlo (AVBMC) algorithm. Incorporated in the Monte Carlo method, is an efficient embedded atom method (EAM) potential developed by the authors. In general agreement with previous empirical studies, the lowest-energy copper structures adapt a single icosahedral structural motif, with pentagonal bipyramid geometry as the building block. However, contrary to studies that describe gold as less symmetric, this work demonstrates that gold clusters adapt both an icosahedral and icositetrahedral structural motifs with many clusters having symmetric geometries. To demonstrate the validity of the results, first-principles calculations utilizing the density functional theory (DFT) were performed on Cu(38), Au(38), and Au(56) clusters for which controversial results had been reported.