Density-functional global optimization of gold nanoclusters

The structure of gas-phase gold clusters of size ~20 is studied by density-functional global optimization in the full configuration space. The putative global minimum of Au₂₀ is confirmed to be a tetrahedron (Td) 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 Td is rationalized in terms of the synergic effects of s-d hybridization and electronic shell closure. Calculations on Au₁₆ and Au₁₈ show that Td Au₂₀ possibly represents a ``unicum'' in the sequence of gold clusters.