  We develop a modified Poisson-Nernst-Planck model which includes both the
long-range Coulomb and short-range hard-sphere correlations in its free energy
functional such that the model can accurately describe the ion transport in
complex environment and under a nanoscale confinement. The Coulomb correlation
including the dielectric polarization is treated by solving a generalized
Debye-H\"uckel equation which is a Green's function equation with the
correlation energy of a test ion described by the self Green's function. The
hard-sphere correlation is modeled through the modified fundamental measure
theory. The resulting model is available for problems beyond the mean-field
theory such as problems with variable dielectric media, multivalent ions, and
strong surface charge density. We solve the generalized Debye-H\"uckel equation
by the Wentzel-Kramers-Brillouin approximation, and study the electrolytes
between two parallel dielectric surfaces. In comparison to other modified
models, the new model is shown more accurate in agreement with particle-based
simulations and capturing the physical properties of ionic structures near
interfaces.
