In the simulations carried out in this work, as well as the work of Amber ff15ipq and OPLS-AA/M, the low β backbone populations present result in a high 2 J(N, C α ) error for the second and third set of Karplus parameters. The pentapeptide conformation with the largest population is PPII with 62 ± 2 % of the simulation spent in this conformation (Table ). This is similar to the conformational propensity observed for OPLS-AA/M (53.5 ± 0.2 %). Both force fields also result in a low α-helical population, which is consistent with experimental data. 6: The ψ and φ distribution for the glycine tetrapeptide (all residues are included) using a) the QUBE force field and b) OPLS-AA/M, 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.