Is 2D graphite an ultimate large hydrocarbon?: III.: Structure and energy spectra of large polybenzenoid hydrocarbons with different edge structures

The structure and energy spectra of very large polybenzenoid alternant hydrocarbons (with up to N similar to 10(3) C-atoms) with different edge structures and defects were investigated theoretically. In all the cases, the calculated values of the energy gap width tend monotonically to a value different from zero when the electron correlation is taken into account. Typical surface (Tamm) states. namely non-bonding MOs, appear in the cases of non-Kekule, open-shell hydrocarbons featuring point defects with a definite topology. The electrons occupying the non-bonding MOs are ferromagnetically coupled. These hydrocarbons are in fact polyradicals with a substantial value of the specific pi-electron energy, which determines their relative stability. (C) 2003 Published by Elsevier Science B.V.