Accurate method for obtaining band gaps in conducting polymers using a DFT/hybrid approach

DFT calculations on a series of oligomers have been used to estimate band gaps, ionization potentials, electron affinities, and bandwidths for polyacetylene, polythiophene, polypyrrole, polythiazole, and a thiophenethiazole copolymer. Using a slightly modified hybrid functional, we obtain band gaps within 0.1 eV of experimental solid-state values. Calculated bond lengths and bond angles for the central ring of sexithiophene differ by less than 0.026 Angstrom and 0.7 degrees from those of the sexithiophene crystal structure. IPs and EAs are overestimated by up to 0.77 eV compared to experimental bulk values. Extrapolated bandwidths agree reasonably well. with bandwidths from band structure calculations.