Molecular-dynamics simulations are increasingly used to study dynamic
properties of biological systems. With this development, the ability of force
fields to successfully predict relaxation timescales and the associated
conformational exchange processes moves into focus. We assess to what extent
the dynamic properties of model peptides (Ac-A-NHMe, Ac-V-NHMe, AVAVA, A10)
differ when simulated with different force fields (AMBER ff99SB-ILDN, AMBER
ff03, OPLS-AA/L, CHARMM27, and GROMOS43a1). The dynamic properties are
extracted using Markov state models. For single-residue models (Ac-A-NHMe,
Ac-V-NHMe), the slow conformational exchange processes are similar in all
force fields, but the associated relaxation timescales differ by up to an
order of magnitude. For the peptide systems, not only the relaxation
timescales, but also the conformational exchange processes differ considerably
across force fields. This finding calls the significance of dynamic
interpretations of molecular-dynamics simulations into question
