where µ M e is an intrinsic material property and independent of the electrode potential. ∆ M S ϕ = ϕ M -ϕ S stands for the inner potential difference, i.e. the electrostatic potential difference between the bulk of electrode (M ) and solution (S) as shown in Figure . K is a constant and depends on the chosen scale, which in DFT simulations is typically chosen as the electrostatic potential in vacuum or the inner potential of the implicit solvent, in which case U M vac (abs) = -μ M e = -E DF T f . The CIP method uses a different reference electrode scale, a "free" electron in solution in which case K = μR,M e for the reference electrode R made of the same material as M .