STRUCTURE OF INHOMOGENEOUS DIPOLAR FLUIDS - A DENSITY-FUNCTIONAL APPROACH

A density functional approach is developed for inhomogeneous dipolar f luids consisting of dipolar hard spheres in presence of external elect ric fields. The theory is applied to two systems, viz. a confined flui d between two planar charged walls where the field is uniform, and als o a fluid where the dipoles are subjected to a radial field due to a u niformly charged hard sphere ion at the centre. A nonperturbative weig hted density approximation is employed to incorporate the effect of sh ort range hard sphere-like correlations while the long-range effects a re obtained perturbatively. The nonuniform density is expanded in term s of spherical harmonics and the correlation function used as input co rresponds to the mean spherical approximation. In the case of planar g eometry, the calculated density and polarization profiles are quite co mparable with the available simulation and other results. In the prese nce of the radial field, the polarization exhibits oscillations showin g a clear variation of the effective dielectric constant within the in terface. This theory also gives an approximate estimate of the static solvation energy of an ion in a dipolar solvent. (C) 1997 American Ins titute of Physics.