The internal reorganization energy λ of a molecule undergoing hole transfer to the same species can be calculated from four energiesthe energy of the neutral molecule in the lowest energy geometry (E 0 , "Neutral"), the energy of the cation at its lowest energy geometry (E + , "Cation"), the energy of the cation at the geometry of the neutral species (E * + , "Cation@Neutral"), and the energy of the neutral molecule at the geometry of the cation (E * 0 , "Neutral@Cation") (Figure ). The λ can then be calculated from those energies according to the following formula 1: Calculating the internal λ of polythiophenes using density functional theory (DFT) calculations requires two geometry optimizations (of both the neutral and cationic species) and can be computationally expensive, as the calculation time increases with the length the polythiophene chain. Recent work on the approximate density functional GFN2 method has shown accurate geometries and excellent correlation with coupled-cluster methods for conformers . We attempted to correlate reorganization energies computed with GFN2 with those computed with the B3LYP DFT method . As discussed below, no significant correlation was found.