Comparison of DFT functionals for prediction of band gap of conjugated polymers and effect of HF exchange term percentage and basis set on the performance

Abstract

The band gap of conjugated polymers is a decisive parameter for their usage in various applications. That is why, the accurate prediction of band gap values is critical in theoretical design of conjugated polymers. In this study, the best hybrid functional with proper basis set and percentage of HF exchange term has been evaluated, and from this, comparing their agreement with the experimental band gap values of 25 flat conjugated polymer compounds. In this way, the optimization of the method as a function of DFT functional, basis set and percentage of HF exchange term have been done through steps considering one of these three parameters, successively. Interestingly, B3PW91 (followed by B3LYP and X3LYP with little bit higher error) with original HF exchange coefficient is found to be the best method to obtain accurate band gap values. However, changing the basis sets (with the exception of SDD) does not affect the performance of this functional remarkably.