Density-functional study of Au n ( n = 2 – 2 0 ) clusters: Lowest-energy structures and electronic properties

We have investigated the lowest-energy structures and electronic properties of the ${\mathrm{Au}}_{n}(n=2--20)$ clusters based on density-functional theory with local density approximation. The small ${\mathrm{Au}}_{n}$ clusters adopt planar structures up to $n=6.$ Flat cage structures are preferred in the range of $n=10--14$ and a structural transition from flat-cage-like structure to compact near-spherical structure is found around $n=15.$ The most stable configurations obtained for ${\mathrm{Au}}_{13}$ and ${\mathrm{Au}}_{19}$ clusters are amorphous instead of icosahedral or fcc like, while the electronic density of states sensitively depends on the cluster geometry. Dramatic odd-even alternative behaviors are obtained in the relative stability, highest occupied and lowest unoccupied molecular orbit gaps, and ionization potentials of gold clusters. The size evolution of the electronic properties is discussed and the theoretical ionization potentials of ${\mathrm{Au}}_{n}$ clusters compare well with experiments.