Surface lattice dynamics and inelastic He scattering in Cu(111)

Abstract

We present a calculation of the Cu(111) surface dynamics in the framework of the multipole model. The electronic degrees of freedom include dipole and quadrupole deformabilities of the conduction electron density, the multipole expansion points being located at the midpoints between nearest-neighbour ions. The model accounts for the anomalous longitudinal resonance by an increase of dipolar deformability at the surface. Moreover the model explains in a straight-forward way the intense He scattering from the longitudinal resonance via the dipolar and quadrupolar modulations of the surface electron density. The surface dipolar contribution also explains the intense electron scattering from the optical surface resonance localized on the second layer.