The Liquid Surface

Abstract

It will occasion no surprise that, when we come to apply molecular distribution function theory to surfaces, we must generalise some of the concepts. Most obviously, instead of the homogeneity of the one-body density in the bulk liquid, if we have a planar surface perpendicular to the z axis, then one of the basic quantities characterising the liquid surface is the density ρ(z). This, of course, is a particular case of a general local density ρ(r), giving the number of molecules per unit volume at position r. Similarly, we define a two-body function ρ⁽²⁾(r₁, r₂) as the average density of pairs of molecules such that one molecule is situated in the element of volume dr₁ and the other in dr₂.