Density functional theory of nonuniform colloidal suspensions:: 3D density distributions and depletion forces

We present a density functional approach for inhomogeneous charge-stabilized colloidal suspensions which is based on the hybrid weighted-density approximation. Making use of an analytic expression recently proposed for the free energy of the homogeneous system, a free energy functional for the inhomogeneous fluid can be found that is particularly easy to evaluate numerically because of the explicit nature of its input functions. Due to this numerical efficiency our calculation can be extended to relatively large three dimensional systems. After performing various explicit tests of our model we consider the case of two large hard spheres immersed in the suspension and calculate from the 3D density distribution of the fluid the effective pair potential between the spheres. (C) 1999 American Institute of Physics. [S0021-9606(99)50611-9].