Cavity contact correlation function of water from scaled particle theory

The ratio of the number density of solvent molecules just outside a cavity of radius Rc to that in the bulk represents the cavity contact correlation function G(Rc). Experimental determination of G(Rc) for water by means of computer simulations has led to the claim that the shape of this function is a basic manifestation of the structural features of the H-bonded network of water [H.S. Ashbaugh, L.R. Pratt, Rev. Mod. Phys. 78 (2006) 159]. In this Letter, I would like to show that classic scaled particle theory is able to reproduce in a satisfactory manner the experimental G(Rc) values by taking into account two things: (a) the size of a water molecule depends on the interactions in which it is involved, so that the effective diameter of H-bonded molecules is 2.8 إ, whereas the van der Waals diameter of a water molecule is 3.2 إ; (b) at any time, liquid water contains both H-bonded molecules and molecules interacting by means of van der Waals forces.