  The adsorption of atomic oxygen and its inclusion into subsurface sites on
Ag(210) and Ag(410) surfaces have been investigated using density functional
theory. We find that--in the absence of adatoms on the first metal
layer--subsurface adsorption results in strong lattice distortion which makes
it energetically unfavoured. However subsurface sites are significantly
stabilised when a sufficient amount of O adatoms is present on the surface. At
high enough O coverage on the Ag(210) surface the mixed on-surface + subsurface
O adsorption is energetically favoured with respect to the on-surface only
adsorption. Instead, on the Ag(410) surface, at the coverage we have considered
(3/8 ML), the existence of stable terrace sites makes the subsurface O
incorporation less favourable. These findings are compatible with the results
of recent HREEL experiments which have actually motivated this work.
