Effect of adsorbates on surface phonon modes: H on Pd(001) and Pd(110)

Abstract
We investigate the effect of adsorbates on surface vibrations by calculating the phonon spectra of clean and hydrogen-covered (001) and (110) surfaces of Pd. The dynamical matrix of these systems is determined using a model many-body alloy Hamiltonian based on ab initio density-functional results for these systems, with no adjustable parameters for surface properties. The most pronounced effect of hydrogen is a strong softening of the Rayleigh wave on Pd(001) and a hardening of surface modes on Pd(001) and Pd(110) with vibration amplitudes confined to the surface layer.