For the sidechain torsional parameters (Section S3.3), the mean error in the recreation of the QM potential energy scans for the QUBE force field is 1.29 kcal/mol, compared to 1.12 kcal/mol for OPLS-AA/M. Particularly high errors occur for both the χ 1 and χ 2 glutamic acid scans, and the glutamine χ 2 scan. For glutamic acid, the error is also high for the OPLS-AA/M force field parameters, but the rotamer populations remained close to the experimental data, and this may be due to a problem with the functional form used in classical force fields. The OPLS-AA/M error in the potential energy scan for glutamine is roughly half that of the QUBE force field. However, as we will show, the accuracy of the glutamine dipeptide MD simulations is good, and so no further refinement was made to the sidechain torsional parameters in this work.