Theoretical Determination of the Most Stable Structures of Ni_<i>m</i>Ag_<i>n</i> Bimetallic Nanoalloys

The structure of the global total-energy minimum for all bimetallic NimAgn nanoalloys with m + n = N = 2−60 atoms has been identified theoretically by combining the embedded-atom model for the total-energy evaluation with the basin-hopping algorithm for global structure optimization. All global minima structures are found to be related to icosahedra and polyicosahedra, except for some Ni- or Ag-rich clusters for N = 38. Through a careful analysis of the total energy as a function of (m,n), various particularly stable structures can be identified. The results show in most cases that Ag-rich structures are more favored and stable compared with the Ni-rich structures. By analyzing the bond-order parameter and the radial distances, we can demonstrate the existence of core−shell structures with a partial segregation of Ag to the surface of the Ni−Ag clusters.