Although technically defined as two separate quantities in order to relate them to an EDA calculation, polarization and charge transfer are modeled by the same energy function in AmberFD, only differing by a scaling factor of (s pol-ct -1) applied to the charge transfer term. Because of this partitioning in our model, as well as the now apparent underestimate/overestimate of E pol and E ct energies, polarization and charge transfer energies might be better suited to be treated as a combined energy. While an explicit description of charge transfer could instead be used by allowing electron populations to flow from one fragment to another and simply setting s pol-ct = 1, this split creates an obvious and systematic error in each term that can instead be canceled out by considering their sum. The argument for treating E pol and E ct as a combined energy can also analyzed from the point of view of charge transfer contamination. For large basis sets, it has been shown that the polarization energy can become contaminated by charge transfer due to each fragment attempting to compensate for its own incomplete basis sets, and that fragment electric-field response functions (FERFs) have been proposed to provide a better defined basis-set limit. However, if one were to think of these two contributions as existing together in the model, then contamination of E ct is automatically accounted for when considering the sum of their contributions, rather than as separate quantities. Additionally, while we have chosen not to utilize FERFs in our DFT calculations (augmented triple-zeta are the largest basis-sets to be used without FERFs as suggested by Q-Chem), our resulting hydrogen-bonded energy profiles also do not show unreasonable contributions between E pol and E ct (see Figure ) and instead give similar contributions to the total interaction energy between the minimums of each profile. At the very least, the underestimation of E pol also self corrects for this possible contamination, albeit by a small amount. The remaining part of the parameterization involved fitting the Pauli radii and damped dispersion parameters to match the total interaction energy E int of the profiles. We summarize the wellness of the fitting procedure with some examples in Figures and, with further results provided in the supporting information. Additionally, Figure demonstrates the overall fit from all energy components. We also compare the results to AMBER99 with Chen-Garica modifications 6 to emphasize the magnitude of which traditional FF energy terms differ from those parameterized on a DFT decomposition analysis. Figure reveals that the individual energies of E Pauli are the most well-determined components. We find that our approximation for E Pauli using a single exponential function gives more than sufficient results and is less computationally demanding than calculating the actual overlap between two densities. E disp is also well represented by the damped r 6 form, although we had very little doubt that this would be the case given its success applied to DFT calculations as empirical corrections.