Density-functional calculations have been performed to determine optimized geometries and energies of ${\mathrm{C}}_{240}$ using the divide-and-conquer method. Six initial geometries were considered, resulting in convergence to two optimized configurations. The formation energies of the optimized structures are separated by approximately 0.07 eV/carbon atom. The lower-energy structure is highly spherical in agreement with preliminary studies and experimental observations. The higher-energy structure is polyhedrally faceted. The results support the conclusion that the most stable form of large carbon clusters is that of dense spherical caged structures.

• Received 26 January 1994

DOI:https://doi.org/10.1103/PhysRevB.49.8526