First-principles electronic structure calculations for peanut-shaped C120 molecules

Using the first-principles real-space finite-difference method, we have theoretically examined optimized structures and electronic energy levels of three peanut-shaped C₁₂₀ molecules (C₆₀ dimers), namely, P55-, P56-, and P66-C₁₂₀ molecules. Our calculations show that as the number of eight-membered rings included in each C₁₂₀ molecule increases, the total energy becomes large and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap becomes small. For the P56-C₁₂₀ molecule, the LUMO is found to be localized at one C₆₀ component, while for the other molecules, the LUMOs are extended over the entire molecule. This fact is understood from the symmetry/asymmetry in the atomic configuration of the three C₁₂₀ molecules.