Growth regimes of carbon clusters

The relative stabilities are calculated of carbon clusters with up to 60 atoms. Equilibrium geometries have been obtained by combining an adaptive simulated annealing method and a simple tight-binding-type Hamiltonian for total energies. Cn clusters favor one-dimensional structures for n of less than about 20. For n of greater than about 20, closed fullerene cages show a larger stability than both the one- and two-dimensional structures (such as graphite flakes and buckled fullerene 'caps'). Isomers with linear and 'fullerene' structure should coexist near the critical cluster size where n is approximately equal to 20. The C60 fullerene is determined to be the most stable structure, with a binding energy of 6.99 eV/atom. (Author)