Disordered global-minima structures for Zn and Cd nanoclusters

The most stable isomers of zinc and cadmium nanoclusters of the normally geometrically closed shell, ``magic'' sizes of 13, 38, 55, 75, and 147 atoms, are found to be of very low symmetry or disordered. The normally global minimum, highly symmetric, ordered icosahedral structures at 13, 55, and 147 atoms, and the Marks decahedral at 75 atoms, are found to be unstable. The 38-atom fcc truncated octahedron is stable for Zn, but unstable for Cd. The lowest energy configurations were obtained using an n-body Gupta potential and employing a global, evolutive search algorithm. All structures were relaxed with density-functional theory calculations at both the LDA and GGA levels which confirmed the greater stability of the disordered isomers. Structure factors are given for anticipated comparison with experiment.