Quantum electrodynamics near an interface: Polarizability of a pair of adsorbed molecules

The expression for the polarizability of a pair of centrosymmetric systems adsorbed on a dielectric or a metallic surface is given for the first time to our knowledge. Of course, if no surface is present our results can also be applied to the case of interactions between colliding molecules in vacuum. The use of the multipolar Hamiltonian leads to a complete expression of the hyperpolarizability which contains at the same time dispersive and inductive effects. This makes it possible to write down calculations in a very compact and simple form.