The errors for these molecules from the Pedley test set are substantially greater than those observed for the QM9-based test set. For example, the MAE for solvation energy in ACN for the Pedley test set is 3.46 kcal/mol-over 10× larger than the MAE of 0.32 kcal/mol for the QM9 test set. The errors tend to increase with molecule size. As shown in Figure , the MAE for molecules in the Pedley test set generally increases as a function of molecular size and reaches over 10 kcal/mol for molecules with 14 heavy atoms. The increase in error with molecule size is not monotonic, with molecules of size 11 having errors around 2× smaller than errors for molecules with 14 nonhydrogen atoms, but is strong enough that we speculate that the poor performance of our models on the Pedley test set has to do with the issues with capturing the effect of molecular size more than the presence of structural motifs absent from the training set.