Modeling Physical Adsorption on Porous and Nonporous Solids Using Density Functional Theory

The formalism of (nonlocal) density functional theory provides an attractive way to describe the physical adsorption process at the fluid-solid interface. It provides numerical results of analytic precision in a small fraction of the time required by a simulation technique. In particular, the ability to model adsorption in a pore space of slit-like or cylindrical geometry has led to useful methods for extracting pore size distribution information from experimental adsorption isotherms. However, critical comparisons of experimental isotherms with the isotherms predicted by density functional theory have shown important differences when using the usual prescription for the nonlocal free energy density functional. It is clear that these differences would affect the accuracy of such pore size information. We show in this paper how a small modification to the mean field computation of the intermolecular attractive potential results in excellent agreement with experiment for the systems studied.