In contrast to the AMBER simulations, the CHARMM36 simulations yield a twofold too large CCR rate of 2.22 s -1 for VAL70-C γ,2 , and also substantially overestimate the order parameter (S 2 axis = 0.61) compared to NMR. Figure shows that the dynamics of this side chain is underestimated with this force field, with much lower frequency of χ 1 transitions (suggesting a higher energy barrier). In the CHARMM36 simulations, the χ 1 jump dynamics are shifted to time scales beyond τ c . In addition, instead of gauche(-), the trans conformer is the major state with 92% population. The latter observation is not due to the side chain being fully trapped in the trans conformer, which is present in the X-ray structure and hence also at the beginning of the MD simulations, because transitions to other rotamers do occur (albeit infrequently), see Figure .