Density-Functional Study of Au$_{n}$$^{-}$ ($n=16-24$): Atomic and Electronic Structures and Interaction with O$_{2}$

Anionic gold clusters with 16 to 24 atoms are studied using the Born-Oppenheimer local-spin-density molecular dynamics method. The structures of the ground-state clusters and energetically lowest-lying isomers are 3-dimensional, while the ground-state structures of smaller Au$_{n}$$^{-}$ with up to 14 atoms were reported to be planar (H\"akkinen, et al., J. Chem. Phys. 117, 6982 (2002)). The calculated vertical electron detachment energies ($vDE$) are in good agreement with the experimental results (Taylor, et al., J. Chem. Phys. 98, 3319 (1992)); $vDE$'s are smaller for even $n$'s and larger for odd $n$'s, with the exception of $n=16$. Compared to the other even-numbered clusters, Au$_{16}$$^{-}$ exhibits relatively large $vDE$, $vDE$(Au$_{16}$$^{-}$)=4.03 eV. The smallest $vDE$ is measured for $n=20$, $vDE$(Au$_{20}$$^{-} $)=2.71 eV, The adsorption of O$_{2}$ to Au$_{n}$$^{-}$ is also sensitive to the cluster size; the O$_{2}$ adsorption is relatively strong for the even-numbered clusters with the exeption of Au$_{16}$$^{-}$. The O$_{2}$ binding energy, the intramolecular bond-length of O$_{2}$, and the excess charge on O$_2$ correlate strongly with the vertical electron detachment energy of Au$_{n}$$^{-}$.