The dielectric constant of the liquid-vapour surface of a polar liquid

A microscopic drop of a polar liquid in equilibrium with its vapour has been simulated. The Stockmayer potential, Lennard-Jones plus point dipole, gives the simplest realistic polar liquid. The static dielectric constant as a function of radius, epsilon (R),, is evaluated and corresponds quite well to a tanh, or Fermi, function of the radius with a mean position, R epsilon , and a width, D epsilon , similar to the values, R h , and D, for the density profile but displaced by a fraction of a molecular diameter towards the liquid. there appears to be no satisfactory theory for this dielectric profile (which must be the same for a plane surface) at present available.