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 la rge number N (N approximate to 10(3)) of carbon atoms have been studied the oretically. It is shown that in the asymptotic case N --> infinity the ener gy gap (EG) Delta E(N --> infinity) is different from zero if the electron correlation is taken into account; that is, the pi systems calculated shoul d possess semiconductor properties. The results for the Delta E(N --> infin ity) not equal 0 of the hydrocarbons are in qualitative agreement with the results calculated for the EG of three classes of 1-D ladder polymers, whic h can be considered as models of quasi-1-D graphite. With increasing width (L) of the polymers, the band gap Delta E(L --> infinity) approaches a valu e different from zero. The problem of the existence of defect states of hyd rocarbons with vacancies is briefly discussed.