Nucleation of carbon clusters via an accretion model

The growth of carbon clusters by monomer addition, at a constant temperature, is examined via Langevin molecular dynamics simulations. For temperatures comparable to experimental growth conditions, we find for carbon clusters with fewer than ∼20 atoms that ‘‘ringlike’’ structures are the dominant species present. For larger clusters, we find ‘‘spheroidal’’ structures dominate. We find that carbon monomers form bonds only at the surface of the clusters during the growth process. No atom is found to be captured inside the hollow of the cluster during our simulations. A subunit of one pentagon surrounded by five hexagons is found to occur frequently for clusters larger than ∼40 atoms. This structure can be thought of as a precursor for the formation of the ${\mathrm{C}}_{60}$ fullerene.