The φ/ψ distributions for each individual dipeptide are shown in Section S4.2 of the Supporting Information. Generally, similar areas of the φ/ψ distribution are occupied by all the dipeptides. The serine and threonine dipeptides do not sample identical regions to the other dipeptides, which is not unexpected given that they have a separate set of backbone torsional parameters. There are several dipeptides which show populations of left-handed α-helical conformation. High left-handed helical populations have previously caused problems for other force fields. However, since the occupancy of PPII and β regions always remain higher than the the populations of the left-handed α-helical region, reducing the left-handed helical population was not considered a priority in this work. The right-handed α-helical populations are small for all the dipeptides. This is in agreement with experimental results. Figure : a) The φ/ψ distribution extracted from the dipeptide MD simulations, plotted in the form -log(p ψ,φ ) (where p ψ,φ is the probability of a region being occupied). The lighter regions correspond to low probability areas including conformations that are not sampled during the simulation. b) The major conformations observed in protein structures. The right-handed α-helical region is labelled as δ and the left-handed α-helical region as δ .