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In classical density functional theory (DFT) the part of the Helmholtz freeenergy functional arising from attractive inter-particle interactions is oftentreated in a mean-field or van der Waals approximation. On the face of it, thisis a somewhat crude treatment as the resulting functional generates the simplerandom phase approximation (RPA) for the bulk fluid pair direct correlationfunction. We explain why using standard mean-field DFT to describeinhomogeneous fluid structure and thermodynamics is more accurate than onemight expect based on this observation. By considering the pair correlationfunction $g(x)$ and structure factor $S(k)$ of a one-dimensional model fluid,for which exact results are available, we show that the mean-field DFT,employed within the test-particle procedure, yields results much superior tothose from the RPA closure of the bulk Ornstein-Zernike equation. We argue thatone should not judge the quality of a DFT based solely on the approximation itgenerates for the bulk pair direct correlation function.

The standard mean-field treatment of inter-particle attraction in classical DFT is better than one might expect