Au20:: A tetrahedral cluster

Photoelectron spectroscopy revealed that a 20-atom gold cluster has an extremely large energy gap, which is even greater than that of C-60, and an electron affinity comparable with that of C-60. This observation suggests that the AU(20) cluster should be highly stable and chemically inert. Using relativistic density functional calculations, we found that AU(20) possesses a tetrahedral structure, which is a fragment of the face-centered cubic lattice of bulk gold with a small structural relaxation. AU(20) is thus a unique molecule with atomic packing similar to that of bulk gold but with very different properties.