Structural Evolution and Stability Trend of Small-Sized Gold Clusters Au ( = 20-30).

Structural evolution and stability pattern of pure neutral gold clusters Au in the small size range of = 20-30 are examined using density functional theory (DFT) calculations. The equilibrium geometries are either confirmed or determined, and some new ground state structures are identified. The most stable configurations of Au-Au sizes are formed by adding extra gold atoms to the highly stable pyramidal structure of Au, while flat-cage shapes are the best candidates for the global minima of both Au and Au. For larger sizes of = 26-30, pyramidal motifs tend to dominate the lower-lying population rather than tubular conformations as previously reported. The energy gaps, excitation energies, and exciton binding energies are also computed to test out the performance of the computational methods employed. Accordingly, a density functional with long-range exchange effects is highly recommended to quantitatively investigate both the ground and excited states of pure gold clusters.