GROUP-IV COVALENT CLUSTERS - SI-45 AND C-44 VERSUS SI-44 AND C-45

Kaxiras has recently proposed a physically appealing structure for the relatively inert Si45 cluster observed by Elkind, Alford, Weiss, Laakonen, and Smalley. Using empirical potentials and all-electron local-density-functional calculations, we have found that removing the central atom from this structure forms a 44-atom fullerenelike silicon cluster with a nearly identical atomization energy per atom, but removing the central atom from the corresponding 45-atom carbon structure forms a 44-atom carbon fullerene with a significantly higher atomization energy. This key difference between these large silicon and carbon clusters is consistent with experimentally observed cluster distributions and is explained based on the greater tendency for pi-bonding and higher strain energy in carbon.