A Solid State Density Functional Study of Crystalline Thiophene-Based Oligomers and Polymers

We present the results of a molecular modeling study of several thiophene-based oligomers and polymers by solid state density functional theory (DFT) calculations. In particular, we consider two polymers for which limit-ordered crystal structures have been reported by our group, on the basis of powder X-ray data analysis: poly(3-(S)-2-methylbutylthiophene) (P3MBT) and forms I’ and II of poly(3-butylthiophene) (P3BT). The calculations employing the functional by Perdew and Wang (PWC) in conjunction with the double-zeta polarised numerical basis set (DNP) demonstrate that a standard quantum mechanical (QM) approach for solid phases can provide a balanced description of the overall structure and energetics of thiophene-based oligomers and polymers maintaining a moderate computational cost. In addition, the results compare well with those provided by specific force field parameterization developed by our group. In many cases PWC/DNP models show even closer agreement with experimental crystal structures, making it the method of choice for computationally accessible problems. Finally, solid state DFT minimizations confirm that the reported crystal structures of P3MBT and P3BT correspond to well-defined energy minima.