Nonlocal density functional theories of the liquid–gas interface

It is shown that the nonlocal free-energy density functional of the penetrable sphere model yields, in a mean-field approximation, a density profile of finite thickness in which the pair correlation function decays slowly in the transverse directions. This result shows that simultaneous occurrence of a finite interfacial thickness and a slow decay of the transverse correlations is not linked to a local free-energy density functional of the van der Waals type.