We divide the QM9 molecules into a subset used for model training and a second segment used for model evaluation. Following our previous work, we removed 10% of the full dataset (a total of the 13026 molecules) for use as a test set. These molecules were neither used to train the parameters of any of the architectures nor to determine early-stopping criteria employed in the neural network training. Accordingly, we use them as a test dataset that represents data drawn from the same population as the training examples (i.e., molecules of smaller than nine heavy atoms).