Competition between supercluster and stuffed cage structures in medium-sized Ge(n) (n=30-39) clusters.

We have performed an unbiased global search for the geometries of low-lying Ge(n) clusters in the size range of 30</=n</=39 using genetic algorithm incorporated with a tight-binding model. Density functional theory calculations were carried out to further optimize the isomer structures. Ge(n) (n=30-39) clusters prefer the motif of supercluster structures stacked by several stable subunits such as Ge(10) and Ge(6), connecting via a few bridging atoms. Size-dependent cluster properties such as binding energy, HOMO-LUMO gaps, and ionization potentials were discussed and compared with experiments.