The current MB approach has one great advantage over the fragmented-basis one, already noted; namely obvious transferability to larger "linear" alkanes. The transferability of the F-PES is not obvious; however, it does appear that the fragmented basis can be built up for larger hydrocarbons. However, it is not clear that the optimized coefficients for C 14 H 30 can be re-used for larger hydrocarbons. We intend to investigate this important aspect of these PIPs approaches in the future Finally, we note that the current study demonstrates some of the strengths and weaknesses of the widely-known MM3 force field. There is a substantial discrepancy between the MM3 energies and the DFT/B3LYP energies, as shown in Figure . In addition, we see from Table that the energies of the stationary points LM, TS1, TS2 and the Methyl torsion TS are considerably low compared to those on either F-PES or MB-PES and, more importantly, compared to the DFT benchmarks. Finally, Figure shows that the results from MM3 are not in good agreement with calculations of the C1-C14 distance distributions and of the dihedral angle distributions using F-PES or MB-PES. Clearly, the present machine-learned potentials can be used to assess and perhaps improve this and more recent 76 classical force-fields for hydrocarbons. This is a fruitful area for future research.