Density-functional global optimization of gold nanoclusters

The structure of gas-phase gold clusters of size similar to 20 is studied by density-functional global optimization in the full configuration space. The putative global minimum of Au-20 is confirmed to be a tetrahedron (T-d) independently of the choice of the exchange-correlation functional, whereas the structure of the low-lying excited states depends on the theoretical approach. The peculiar stability of T-d is rationalized in terms of the synergic effects of s-d hybridization and electronic shell closure. Calculations on Au-16 and Au-18 show that T-d Au-20 possibly represents a "unicum" in the sequence of gold clusters.