Correlation energy and van der Waals interaction of coupled metal films

Abstract

We derive a general expression for the density response function of two films separated by distance $d$ in terms of the response function of the isolated films. Using the random-phase approximation and a semiclassical infinite-barrier model, we then calculate the total correlation energy of the system and hence the van der Waals interaction of the coupled films. Both of these quantities can be written in terms of the zero-point energy of the normal modes. Explicit calculations of the van der Waals interaction indicate that the dominant contribution is from the surface plasmon modes. The connection between the surface correlation energy and the work done against the van der Waals force is discussed. In the infinite-barrier model these quantities differ by a cleavage energy whose dominant contribution comes from the particle-hole modes and which forms half the surface correlation energy.