CARBON CLUSTER STRUCTURES AND STABILITIES PREDICTED FROM SOLID-STATE POTENTIALS

An empirical potential-energy function comprising two- and three-body terms, whose parameters have been determined from the properties of di amond and graphite, is used to study the structures and energies of ca rbon microclusters. The binding energy per atom of smaller linear clus ters increases monotonically with the number of atoms, whereas cyclic clusters display an optimal energy per atom for six-membered rings. Th e energies of fullerenes' are sensitive to nuclearity and shape, with icosahedral C-60 and D-5h C-70 being the most stable clusters. The pot ential predicts the binding energy of C-60 to be 7.25 eV per atom, in good agreement with experimental measurements. For larger clusters, sp herical fragments of cubic bulk structures have been investigated; dia mond fragments become relatively more stable than other cubic fragment s for more than approximately 100 atoms. Open nanotubes are found to b e most stable for circumferences containing five hexagons. Vibrational frequencies were calculated and correlated with experimental results for some clusters.