IBI models served as both a baseline comparison and as low-level models for training the ∆-models. Two IBI models, with and without pressure-correction (IBI PC and IBI PC , respectively), were parameterized for each system and CG mapping. The IBI models used tabulated potentials for bonds, angles, and non-bonded pairwise interactions and were trained using the same protocols as described in an earlier publication. In brief, all potentials were iteratively updated using a correction proportional to the logarithmic error of the corresponding distribution function. For bond and angle potentials, these were the length and angle distribution functions parsed from the atomistic trajectories; for the pair-wise potentials, these were the radial distribution functions (RDFs). The specific form of the update for each pair-wise potential was