We next examined the potential energy surface generated from moving both peripheral and axial methanol H-bonds away from CV + at the site of the polarized nitrogen. We computed the energies along the H-bond distance coordinate, keeping the remaining solvent fixed. The potentials were generated using (1) the original QUBEKit DDEC6 charges for CV + , (2) the new MK charges for CV + from explicit solvent polarization, which we use to generate a revised QUBEKit force field that we call revQUBEKit, (3) the same electronic structure method as was used in the QM/MM AIMD simulation, with CV + treated with CAM-B3LYP/6-31G(d) and all remaining solvent as MM, and (4) CV + and the H-bonding methanol molecule treated with CAM-B3LYP/6-31G(d) and all remaining solvent as MM, denoted as QM-QM/MM, see Figure . For the peripheral H-bond, the QM/MM, QUBEKit, and revQUBEKit methods all share a potential minima at 1.6 Å. The strength of the H-bonds fall between 10.5 and 12.2 kcal/mol at their minimum interaction distances. For the QM treatment of methanol, the depth of the poten-FIG. . Interaction energies between cresyl violet and a single methanol solvent molecule that forms a peripheral H-bond at the amine group (top) and an axial H-bond at the amine group (bottom). For the QM/MM model, CV + is treated as QM and all solvent as MM. For the QM-QM/MM model, CV + is treated as QM and the H-bonding methanol is treated as QM, with all other solvent as MM. tial well is similar, but the minimum of the well is at a larger distance of 1.9 Å. For the axial H-bond, the original DDEC6 implicit solvent QUBEKit charges produce a very weak potential, with the H-bond only yielding ∼2 kcal/mol of stabilization. In contrast, the QM-MM treatment of the chromophore-methanol interaction, the QM-QM treatment of the chromophore-methanol interaction, along with the revQUBEKit force field generated with the MK charges from explicit solvent configurations, yields 7-8 kcal/mol of stabilization upon forming the axial H-bond. The energy minima for revQUBEKit and CAM-B3LYP with MM solvent are at 1.6 and 1.7 Å distances between the nitrogen and the hydrogen, respectively, with the QM solvent having a minimum at 1.9 Å. Overall, these potentials show that the MK charges used for revQUBEKit produce potentials in good agreement with the QM/MM electronic structure method used for the QM/MM AIMD simulation, but also suggest that a QM treatment of the solvent would lead to similar energetics but larger H-bonding distances.