To help provide insight into the
remarkable catalytic behavior of the oxygen/silver system for heterogeneous
oxidation reactions, purely sub-surface oxygen, and structures involving
both on-surface and sub-surface oxygen, as well as oxide-like structures
at the Ag(111) surface have been studied for a wide range of coverages
and adsorption sites using density-functional theory. Adsorption on the
surface in fcc sites is energetically favorable for low coverages, while
for higher coverage a thin surface-oxide structure is energetically favorable.
This structure has been proposed to correspond to the experimentally observed
(4x4) phase. With increasing O concentrations, thicker oxide-like structures
resembling compressed Ag2O(111) surfaces are energetically favored.
The present studies, provide a comprehensive picture of the behavior and
chemical nature of the interaction of oxygen and Ag(111), as well as of
the initial stages of oxide formation. [W.-X. Li, C. Stampfl, and M. Scheffler,
Phys. Rev. B 67, 064108 (2003)]