Where A is the surface area, σ is the surface charge density, and U is the potential. To obtain these capacitance curves from our discrete data we interpolate and employ numerical derivatives. Interpolations are done using Piecewise Cubic Hermite Interpolating Polynomials (PCHIP) to avoid any 'overshoot' issues that can occur with classical cubic splines and to ensure the preservation of monotonicity. Results are shown for the three models in Figure . For RISM models, we report Fermi energy fluctuations which can be close to 0.05 eV. Such small fluctuations do not change the conclusion for singular values, but derivatives will not be easily calculated without smoothing. For this reason, both Figures and have been fitted using a smoothing spline to allow observable trends. However, on a larger potential scale with larger steps, these fluctuations will be less impactful. Both RISM models give higher capacitances than the CANDLE model at the PZC, with 36 µF/cm 2 for the RISM (TIP5P) and 25 µF/cm 2 for the RISM (SPC) model. At high electrolyte concentration (1.0 M), higher capacitances are expected and are in good agreement with experimental studies.