Understanding the Density Functional Dependence of DFT-Calculated Electronic Couplings in Organic Semiconductors.

We present an analysis of the magnitude of density functional theory (DFT)-calculated intermolecular electronic couplings (transfer integrals) in organic semiconductors to give insight into the impact that the choice of functional has on the value of this parameter, which is particularly important in the context of charge transport. The major factor determining the magnitude of the calculated transfer integrals is the amount of nonlocal Hartree-Fock (HF) exchange within a given functional, with the transfer integrals increasing by up to a factor of 2 when going from 0 to 100% HF exchange for a series of conventional functionals. We underline that these variations in the transfer integrals are in fact to be expected, with the computed transfer integrals evolving linearly with the amount of HF exchange. We also use a long-range corrected functional to tune the contributions of (semi)local and nonlocal HF exchanges and highlight their respective roles as a function of intermolecular separation.