Structure and properties ofC60dimers by generalized tight-binding molecular dynamics

Recent Raman-scattering investigations of visible- or ultraviolet-irradiated solid ${\mathrm{C}}_{60}$ film have revealed that the film consists of photopolymerized fullerene molecules with covalent intermolecular bonding in contrast to the weak van der Waals type bonding found in the crystal. In this report various ${\mathrm{C}}_{60}$ dimer geometries are studied to determine the most stable dimer configuration, using a recently developed generalized tight-binding molecular-dynamics technique. Comparison of calculated properties with experimental results strongly suggests that the linkage between ${\mathrm{C}}_{60}$ monomer units is across parallel double bonds reforming into a four-sided ring, giving a ‘‘dumbbell’’ structure.