Double-layer effects. Cation adsorption/desorption on metallic or oxide surfaces induces a relatively large dipole moment at the interface , which interacts with the interfacial electric field caused by the electrode potential. Since the electrode potential is not explicitly accounted for in periodic DFT calculations, the Gibbs free energy needs to be corrected for this effect. Following the approach presented by Mills et al. for cation adsorption on fcc(111) electrode surfaces , Eq. 4 can be rewritten as,