On-surface and sub-surface oxygen adsorption on Ag(2Â 1Â 0): Vibrational properties

In this work we investigate the vibrational properties of atomic oxygen on Ag(2 1 0) in a mixed on-surface + sub-surface adsorption configuration using density-functional perturbation theory. In particular, we consider a geometry in which oxygen decorates the steps and an additional O species is located in an octahedral sub-surface site just below an Ag step atom. This structure presents a mode at 55 meV due to the coupled vibration of on-surface and sub-surface O species, which is close to that observed in HREEL spectra.