We choose s pol-ct to be a greater than 1 so that the charge transfer correction continues to lower the interaction energy. In the next section, we will describe in detail the fitting procedure used to determine s pol-ct and other parameters in the model. For now, we will simply state that using such a scaling factor also allows for future improvements of the AmberFD model in which the actual transfer of electron populations between nucleobases could be allowed via newly introduced energy terms and instead set s pol-ct = 1.