4 Parameterization Results charges in Adenine and Guanine, which are opposite in sign to those in AMBER99. We attribute this effect to be from the N7 site having a more dipole-like distribution with its lone pair and the C9 methyl carbon being slightly negative. This is not a concern, as these sites will not be participating in hydrogen bonding as much as the more polar parts of the molecule and end up having some of the largest Pauli radii (greater than 3.3 Å) that also contribute to less probable H-bonding. Dipole moments before and after correcting for E elec are shown in Table . While the DRESP method provides us with nearly identical dipole moments as those from DFT calculations, optimizing the scaling factors s frz and τ frz to improve the agreement with E elec lead to approximately a 13% increase in the magnitude of the charges and less than a 5% decrease in the density exponents (which increases it's diffusivity). It is a bit disappointing that the dipole moments are not maintained through this process, yet the use of spherical, atom centered densities, regardless of the inclusion of lone-pair sites, is still an approximation that should not be expected to completely model the full electrostatic interaction Scaling of the charges and exponents had a rather significant improvement to the electrostatic energy for hydrogen-bonded geometries, as seen in Figure . Especially for profiles that change along the direction of the hydrogen bonds (x), the comparison to the QM energy Refinement" refers to the energy profiles obtained using only the DRESP determined charges and exponents, while "With Refinement" curves are obtained after scaling these parameters.