Is 2-D Graphite an Ultimate Large Hydrocarbon? 1. Energy Spectra of Giant Polycyclic Aromatic Hydrocarbons

The energy spectra of three classes of polybenzenoid hydrocarbons with a large number N (N ≈ 103) of carbon atoms have been studied theoretically. It is shown that in the asymptotic case N → ∞ the energy gap (EG) ΔE(N→∞) is different from zero if the electron correlation is taken into account; that is, the π systems calculated should possess semiconductor properties. The results for the ΔE(N→∞) ≠ 0 of the hydrocarbons are in qualitative agreement with the results calculated for the EG of three classes of 1-D ladder polymers, which can be considered as models of quasi-1-D graphite. With increasing width (L) of the polymers, the band gap ΔE(L→∞) approaches a value different from zero. The problem of the existence of defect states of hydrocarbons with vacancies is briefly discussed.