The structure of gas-phase gold clusters of size $\sim 20$ is studied by density-functional global optimization in the full configuration space. The putative global minimum of ${\mathrm{Au}}_{20}$ is confirmed to be a tetrahedron $\left(T_d\right)$ 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 $s\text{−}d$ hybridization and electronic shell closure. Calculations on ${\mathrm{Au}}_{16}$ and ${\mathrm{Au}}_{18}$ show that $T_d$ ${\mathrm{Au}}_{20}$ possibly represents a “unicum” in the sequence of gold clusters.

• Received 27 January 2006

DOI:https://doi.org/10.1103/PhysRevB.73.205414