Extensive density-functional theory calculations, and taking into account temperature and pressure through consideration of the oxygen chemical potential, affords a comprehensive picture of the behavior and interaction of oxygen and Ag(111), and provides valuable insight into the function of silver as an oxidation catalyst. The obtained phase-diagram reveals the most stable species present in a given environment and thus identifies (and excludes) possibly active oxygen species. In particular, for the conditions of ethylene epoxidation, a thin oxide-like structure is most stable (orange region in the below phase diagram), suggesting that such atomic O species are actuating the catalysis, in contrast to hitherto proposed molecular-like species. [W.-X. Li, C. Stampfl, and M. Scheffler, Phys. Rev. Lett. in press.]

The temperature-pressure phase diagram showing the energetically most favorable structure for a give pressure and temperature: from red to blue, bulk disilver oxide, thin (4x4) surface oxide, low coverage of chemisorbed oxygen, and the clean Ag(111) surface.

The same as the above P-T phase diagram except showing more structures and only two pressures are considered, namely, those corresponding to typical ultra high vacuum (UHV) conditions and to atmospheric pressures, typical of catalysis. The colored panels indicate the regions of phase stability.