This unphysical behavior stems from the similar lengthscales of the intramolecular bonds and the first shell intermolecular neighbors. If the distance between bead and its intermolecular neighbor is less than its bonded neighbor, the NN mistakenly applies the constraining force to the intermolecular neighbor instead of the bonded neighbor, and in the absence of these forces, the real bonded-neighbor drifts away. A representative snapshot of two PEG M1 molecules is shown as an example (Fig. )), where the distance between blue and orange beads in different molecules (3.67 Å) is less than between their actual bonded neighbors (3.8 and 4.16 Å). This behavior was also observed for the R4 mapping of butanol, but not for R2 and R3 mappings within the timescale of these simulations (Fig. )).