The simulations of the PEG system with the ML model exhibited unphysical dynamics; it is for this reason that its results are denoted by a hatched bar in Figure and that the discussion of these results was deferred. As the simulation progresses, bonded neighbors drift apart to be replaced by intermolecular beads in the first coordination shell (Fig. ). After the exchange, forces typical of intramolecular interactions occur between these beads, effectively creating a new bond. This does not show up during training, because the loss function is only based on reproducing the forces for configurations sampled from the atomistic ensemble. Of course, this behavior is entirely inconsistent with the atomstic dynamics, but it nevertheless still results in the correct force distribution and comparable property errors to the other models. This illustrates the peril of using ML models that can minimize loss functions while violating elementary physical constraints.