A simple way of understanding the nonadditivity of van der Waals dispersion forces

Using a semiclassical model for three interacting fluctuating dipoles we introduce a simple scenario in which the nonadditivity of the van der Waals dispersion forces arises in a very transparent way. For simplicity, we illustrate our model in the case of nonretarded dispersion forces. The argument can be straightforwardly generalized to the case of N interacting fluctuating dipoles. For pedagogical reasons, we also give a brief review of some basic points concerning van der Waals forces.