Band-gap calculations for squarelene-based polymers

The electronic structures and band-gaps, modeled as the energy difference between ground singlet state and excited triplet state, for a series of oligomers of a polymer based on squarelene and fused thiophenes were investigated. AM1 and PM3 semi-empirical, Extended Hiickel Theory (ETH), Hartree-Fock (HF) and second-order Mِller-Plesset perturbation (MP2) ab initio, numerical atomic orbital basis set density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations are employed. The results indicate that a narrow gap less than 0.5 eV could be reached in a long polymer .