Nonlocal theory of surface tension in simple liquids

We consider a method for singling out the surface contribution in the form of a nonlocal functional of the transition-layer structure function from the general expression for the thermodynamic potential of the two-phase liquid–vapor system. A possibility of using the relation between the thermodynamic potentials of equilibrium volumetric and surface phases to modify the resulting expansion is indicated. We obtain an analogue of Euler's first integral in the variational problem for the surface-energy functional and give some estimates for the parameters characterizing the surface layer and its asymptotic properties.