However, PB theory is only valid for dilute solutions. It is missing the short range correlations due to steric interactions as well as long range electrostatic correlations. These shortcomings in PB theory are the motivation behind subsequent development in more advanced approaches including statistical field theory, 69-73 classical density functional theory (cDFT), 74,75 integral equations, 76 and Landau-Ginzburg type functionals. Validation of these theories by comparison to experiment or molecular simulation continues to provide insight into the nature of the EDL.