From oligomers to polymer: Convergence in the HOMO-LUMO gaps of conjugated oligomers

Extrapolation of HOMO-LUMO gaps for pi-conjugated oligomers at the B3LYP/6-31G(d) level of theory predict accurately (within 0.1-0.2 eV) the band gaps of conjugated polymers only when long (at least 20-mer) pi-conjugated oligomers are used for the extrapolation.