Structure, stability and electronic property of the gold-doped germanium clusters: AuGen (n=2-13)

The structure, stability and electronic property of the AuGen (n = 2-13) clusters with different spin configurations are systematically investigated with density-functional theory approach at UB3LYP/LanL2DZ level. In examining the lowest energy structures, it is found that the growth behaviors for the small-sized AuGen (n = 2-9) clusters and relatively large-sized AuGen (n = 10-13) clusters are different. As the number of Ge atom increases, the Au atom would gradually move from convex to surface and to interior sites. For the most stable structures of AuGen (n = 10-13) clusters, the Au atom would be completely surrounded by the Ge atoms to form Au-encapsulated Ge-n cages. Natural population analysis shows that the charges always transfer from the Au atom to the Ge-n framework except for the AuGe2 cluster. This indicates that the Au atom acts as electron donor even the 5d orbitals of the Au atom are not significantly involved in chemical bonding. The analyses of the average atomic binding energies as well as the dissociation energies and the second-order differences of total energy show that the AuGen clusters with n = 5, 9 and 12 are more stable than their neighboring ones, in which the bicapped pentagonal prism AuGe12 in D-2d symmetry is most stable. The highest occupied molecular orbital-lowest unoccupied molecular orbital gaps are explored to be in the region of semiconductors and the more stable clusters have slightly smaller gaps. It could be expected that the stable clusters might be considered as the novel building blocks in practical applications, e. g., the cluster-assembled semiconductors or optoelectronic material.