Investigations of diamond–graphite hybrids and fullerenes with seven-membered rings

The nature of diamond–graphite hybrids has been studied by molecular mechanics, by examining the structures of species such as C₈₄H_x wherein the sp³ to sp² carbon ratio is varied progressively. The dependence of the average coordination number on the atom fraction of hydrogen has been examined in the light of the random covalent network model. The HOMO–LUMO gap has been estimated in a graphite-like C₁₁₀H_x and in a diamond-like C₁₂₀H_x as a function of the sp³/sp² carbon atom ratio. The gap increases exponentially with the fraction of sp³ carbon. Shapes of fullerene-like structures with 7-membered rings, in addition to 6- and 5-membered rings, have been investigated along with structures of bent nanotubes having similar ring systems.