AmberFD is based up on optimizing RNA nucleobase interactions to match those from a specified set of EDA calculations. We are borrowing the "Amber" name as the remaining bonded parameters (including bond, angle, and torsional spring constants), as well as all sugar-phosphate interactions are copied over. The only interactions in this model that are replaced are those between two nucleobases. Glycosidic torsions and overall backbone flexibility has already been established in previous works, and the added complexity of parameterizing such terms is beyond the effort required to establish the feasibility of a model. As such, we maintain all sugar-base and phosphate-base interactions as originally used in AMBER99 with modifications from Chen and Garcia 6 A question that arises for all polarizable force fields is how to assign the extent to which molecules are polarized. That is, if two nucleobases each polarize each other, how do we quantify the appropriate amount of induction? A way of dealing with this problem is to utilize a decomposition scheme of quantum mechanical energies and fit our model to the polarization energy directly. In this work, we choose to use the energy decomposition analysis (EDA) for density functional theory based on Absolutely Localized Molecular Orbitals (ALMO). EDA has been discussed extensively in the literature, but for completeness and to clarify which versions of the framework are being used, we will briefly review the method. As depicted in Figure , the total interaction energy between two or more fragments E int are decomposed into three main contributions, frozen fragments energies E frz , polarization E pol , and charge transfer E ct . Frozen energies, say for two fragments A and B, are computed by subtracting the individual ground-state energies E[Ψ A ] and E[Ψ B ] of each fragment from the total energy of the combined system