Density functional theory of simple polymers in a slit pore. II. The role of compressibility and field type

Simple tangent, hard site chains near a hard wall are modeled with a densit y functional (DF) theory that uses the direct correlation function, c(r), a s its "input." Two aspects of this DF theory are focused upon: (1) the cons equences of variations in c(r)'s detailed form; and (2) the correct way to introduce c(r) into the DF formalism. The most important aspect of c(r) is found to be its integrated value, c(0). Indeed, it appears that, for fixed c(0), all reasonable guesses of the detailed shape of c(r) result in surpri singly similar density distributions, rho(r). Of course, the more accurate the c(r), the better the rho(r). As long as the length scale introduced by c(r) is roughly the hard site diameter and as long as the solution remains liquid-like, the rho(r) is found to be in good agreement with simulation re sults. The c(r) is used in DF theory to calculate the medium-induced potent ial, U-M(r), from the density distribution, rho(r). The form of U-M(r) can be chosen to be one of a number of different forms. It is found that the fo rms for U-M(r)which yield the most accurate results for the wall problem ar e also those which were suggested as accurate in previous, related studies. (C) 2000 American Institute of Physics. [S0021-9606(00)53005-0].