  Electrostatic correlations and variable permittivity of electrolytes are
essential for exploring many chemical and physical properties of interfaces in
aqueous solutions. We propose a continuum electrostatic model for the treatment
of these effects in the framework of the self-consistent field theory. The
model incorporates a space-or field-dependent dielectric permittivity and an
excluded ion-size effect for the correlation energy. This results in a
self-energy modified Poisson-Nernst-Planck or Poisson-Boltzmann equation
together with state equations for the self energy and the dielectric function.
We show that the ionic size is of significant importance in predicting a finite
self energy for an ion in an inhomogeneous medium. Asymptotic approximation is
proposed for the solution of a generalized Debye-Huckel equation, which has
been shown to capture the ionic correlation and dielectric self energy. Through
simulating ionic distribution surrounding a macroion, the modified
self-consistent field model is shown to agree with particle-based Monte Carlo
simulations. Numerical results for symmetric and asymmetric electrolytes
demonstrate that the model is able to predict the charge inversion at high
correlation regime in the presence of multivalent interfacial ions which is
beyond the mean-field theory, and also show strong effect to double layer
structure due to the space- or field-dependent dielectric permittivity.
