Structure and energetics of CuN clusters with (2≤N≤150):: An embedded-atom-method study

We use the embedded-atom method (EAM) in the version of Daw, Baskes, and Foiles (DBF) to determine the three most stable isomers of Cu-N clusters with N from 2 to 150. Randomly generated initial configurations are optimized with the variable metric/quasi-Newton method combined with our own Aufbau/Abbau algorithm for searching the global minima. A detailed comparison is made for clusters with up to 60 atoms obtained with the DBF and the Voter-Chen (VC) versions of the EAM, the many-body Gupta, and the Sutton-Chen 9-6 potentials. Although the two EAM potentials have completely different parametrizations, they yield clusters that are structurally and energetically almost identical. On the other hand, the Sutton-Chen potential strongly overestimates the binding energy of the dimer and the small copper clusters with up to 15 atoms, and therefore, yields clusters with shorter bond lengths. For DBF clusters with up to 150 atoms we analyze many structural and energetic properties such as the overall shape, the construction of atomic shells, the similarity of the clusters with fragments of the fcc crystal or of a large icosahedral cluster, and whether the N-atom cluster resembles the (N-1)-atom one with an extra atom added. The most stable clusters have high symmetry, such as the magic-sized Cu-55 and Cu-147 that are the second and third Mackay icosahedra, where the latter was obtained for the first time in a completely unbiased structure optimization. The cluster growth is predominantly icosahedral, with islands of fcc, tetrahedral, and decahedral growth.