The equilibrium structures of giant fullerenes: faceted or spherical shape? An ab initio Hartree-Fock study of icosahedral C240 and C540

Ab initio self-consistent field (SCF) Hartree-Fock (HF) geometry optimizations employing minimal basis indicate the existence of a single, faceted polyhedral equilibrium structure in the potential energy surface of C240 and C540. These results are in contrast with recent divide-and-conquer density functional predictions for C240 which found a lowest energy isomer of spherical nature. The present theoretical predictions are compared with available experimental information on these giant fullerenes. The C540 calculation in this work involves 2700 basis functions and is the largest Hartree-Fock calculation reported to date.