Before proceeding with details of training and testing, we examine the validity of the assumption that the MM3 force field provides a realistic dataset of configurations to obtain DFT energies and gradients. This is addressed in Figure , where correlation plots of MM3 energies against B3LYP ones are given for data collected at 500 K, 1000 K and 2500 K. As seen, there is qualitative correlation with the B3LYP energies, which span a large range from roughly 20,000 cm -1 to nearly 180,000 cm -1 . This is a good indicator that the MM3 calculations do provide a diverse dataset of configurations, which was the goal. Clearly though, there are large differences in the MM3 energies relative to the B3LYP ones, differences that provide strong motivation for going beyond the MM3 force field with the ML PESs we report here. Additional results showing DFT and MM3 energy histograms from the three temperatures and histograms correlated with the C1-C14 distance are given in the Supporting Information (SI).