  The modified Poisson-Boltzmann theory of the restricted primitive model
double layer is revisited and recast in a fresh, slightly broader perspective.
Derivation of relevant equations follow the techniques utilized in the earlier
MPB4 and MPB5 formulations and clarifies the relationship between these. The
MPB4, MPB5, and a new formulation of the theory are employed in an analysis of
the structure and charge reversal phenomenon in asymmetric 2:1/1:2 valence
electrolytes. Furthermore, polarization induced surface charge amplification is
studied in 3:1/1:3 systems. The results are compared to the corresponding Monte
Carlo simulations. The theories are seen to predict the "exact" simulation data
to varying degrees of accuracy ranging from qualitative to almost quantitative.
The results from a new version of the theory are found to be of comparable
accuracy as the MPB5 results in many situations. However, in some cases
involving low electrolyte concentrations, theoretical artifacts in the form of
un-physical "shoulders" in the singlet ionic distribution functions are
observed.
