3) F(0)tot contribution (eqn. 2) through a simultaneous HD-SHG/HD-SFG experiment has not yet been achieved, the non-resonant c values reported here are obtained directly through eqn. 4 and comparison to atomistic simulations is possible: the first approach calculating c values for a charged interface (oxide:salt solution) was pioneered in 2019 by Chen and Singer, 75 focusing on the polarization of the water molecules. This method was recently expanded by us and the Miller group to include surface hydroxyl groups, the second-most abundant interfacial species besides water at oxide:water interfaces. While that approach distinguished contact ion pairs from solventseparated ion pairs and showed the presence of the former recapitulated the experimentally observed trends in c , ion specific effects were not pursued in that study.