The persistence of the underpredicted region even on the training set demonstrated that the model was unable to predict the energies of data that it was explicitly trained on, which is indicative of an underlying issue with the DFT data. We later found that these poorly predicted structures were primarily the iron-group metals, namely Fe, Ru, and Os, which we will discuss more later. This pattern motivated the creation of tmQM wB97MV, as we hypothesized that adding diffuse basis functions and employing the consistently highperforming ωB97M-V functional would yield more reliable DFT data, which would avoid the observed region of underprediction.