Nucleation of carbon clusters

The growth of carbon clusters by monomer addition, at constant temperature, is examined via Langevin molecular-dynamics simulations by using a recently developed many-body interatomic potential for carbon. The simulations are performed at temperatures below the melting point of graphite. We find for carbon clusters with fewer than ∼20 atoms that ‘‘ringlike’’ structures are the dominant species present. ‘‘Spheroidal’’ structures dominate for larger clusters of sizes above ∼30 atoms. It is found that carbon monomers form bonds at the surface of the spheroidal cluster during the process of cluster growth. No monomer is found to be captured inside the hollow of a spheroidal cluster during the simulation. A subunit of one pentagonal ring surrounded by five hexagonal rings in the cluster is found to appear frequently for clusters of sizes larger than ∼40 atoms. This structure can be thought of as a precursor for the formation of the ${\mathrm{C}}_{60}$ fullerene.