Whilst developing QUBE, manual adjustments to some torsional parameters were required. This was also required in the development of OPLS-AA/M, and we can infer from this that automatically fitting backbone and sidechain torsional parameters using dihedral energy scans is still challenging. The most obvious failure of dihedral energy scan fitting was that for a number of sidechains it was more accurate to set the torsional parameters to zero than to use the originally derived terms. This is in part due to the functional form used, with potential improvements to this discussed below, but is also due to the poor sampling of relevant structures by scanning one or two dihedral angles at a time. This problem is reduced by the iterative fitting methods used in AMBER ff14ipq and ff15ipq, 2,38 which sample the structures used for torsional parameter fitting by performing MD simulations with the current iteration of the force field. This approach will be considered in future versions of the force field.