Comment on "Martini force field for protonated polyethyleneimine".

We comment on the recently published Martini forcefield for linear polyethylenimine (Beu et al., J. Comput. Chem., 2020, 41, 349). With supporting evidence, we demonstrate that the new coarse-graining methodology presented in that work is inconsistent with the Martini methodology and lacks important validation steps which is usually required by Martini forcefields.