Stability and transformation of 20-atom carbon clusters

We report results of ab initio calculations on structural properties of 20-atom carbon clusters including the ring, the corrannulene and the dodecahedron. The corrannulene and the ring are energetically less stable than the dodecahedron for both the neutral and the singly-charged states. The clusters have well-defined ionization potentials and electron affinities. The structural transformation of these clusters can occur through a series of "concerted exchange" and bondbreaking (or bond formation). The barrier heights for the transformation and the structures at the saddle points are investigated at the initial stage of transformation from the corrannulene to the other isomers. The barrier heights even at the initial stage are found to be substantial. The results explain the abundance of the ring structure in experiments.