Nature of surface-phonon anomalies in noble metals

We propose a new approach to describe the many-body effects in the lattice dynamics of metals. We represent here the electron charge density in each unit cell by an expansion over the multipole moments, where the coupling of the fluctuating multipoles to ion displacements gives rise to the observed many-body effects. This model reproduces the observed surface-phonon dispersion curves and explains also their anomalous features.