AbstractThe frequency of the dipolar surface of small particles is calculated using the sum rule techniques due to Lushnikov et al. The effect of surface diffuseness of electron density is included. The screening of the electrons is described within the Thomas‐Fermi approximation. The lattice structure and the lattice relaxation through the introduction of pseudopotentials are taken into account. The ground state charge density is obtained from a variational estimate of the total energy of the clusters based on the local density functional formalism. The surface plasmon frequency is red‐shifted from its classical va