Structure and structural evolution of Agn (n=3–22n=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 Agn clusters in a size range of n=3–22n=3–22 were studied. The Agn (n=9–16n=9–16) clusters prefer compact structures of flat shape, while the Agn(n=19,21,22) clusters adopt amorphous packing based on a 13-atom icosahedral core. For Ag16, 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 Ag17 and Ag18: hollow-cage structures versus icosahedron-based compact structures. The lowest-energy structure of Ag20 is a highly symmetric tetrahedron with TdTd 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 Agn (n=3–22n=3–22) clusters were computed and compared with experimental values.