Structure and structural evolution of Agn (n=3-22) clusters using a genetic algorithm and density functional theory method

Using a genetic algorithm followed by local optimization with density functional theory, the lowest-energy structures of Ag-n clusters in a size range of n = 3-22 were studied. The Ag-n (n = 9-16) clusters prefer compact structures of flat shape, while the Ag-n (n = 19, 21, 22) clusters adopt amorphous packing based on a 13-atom icosahedral core. For Ag-16, two competitive candidates for the lowest-energy structures, namely a hollow-cage structure and close-packed structures of flat shape, were found. Two competing candidates were found for Ag-17 and Ag-18: hollow-cage structures versus icosahedron -based compact structures. The lowest-energy structure of Ag-20 is a highly symmetric tetrahedron with Td symmetry. These results are significantly different from those predicted in earlier works using empirical methods. The ionization potentials and electron affinities for the lowest-energy structures of Ag-n (n = 3-22) clusters were computed and compared with experimental values. (C) 2007 Elsevier Ltd. All rights reserved.