In addition, we considered a correlation of λ between shorter and longer oligomers (Figure ), since shorter oligomers are faster to optimize. We did not find such a correlation between the B3LYP-computed λ of the dimer and tetramers, or the dimers and hexamers. We did find, however, a good correlation between the tetramers and hexamers (Figure ). Thus, to develop an adequate training set, more tetramers than hexamers can be used, considerably reducing the calculation time. We therefore used a data set made up of mainly tetramers plus a small number of hexamers. We increased the training set in batches until we saw no significant improvement in the model score (Figure ) and decrease in RMSE. Our final data set consisted of 7020 tetramers and 408 hexamers with B3LYPcalculated λ between 0 and 2 eV. We chose this range as we assumed that oligomers with λ larger than 2 eV are irrelevant to our study.