(394a) Surface Oxides: Thermodynamics and Energetic Correlations for Surface Oxides of Transition Metal Surfaces

Adsorption energy correlations for simple adsorbates over a variety of transition metal surfaces have been previously demonstrated. These correlations exist due to the shared d-band bonding mechanism simple atomic adsorbates such as O, N, and C demonstrate on transition metal surfaces. Additionally O adsorption on a wide variety of metal surfaces has been studied in depth, including phase behavior studies which allow comparison to experimental results.

Rather than observing high coverage oxygen chemisorbed species, experimental studies of oxygen adsorption on transition metal surfaces frequently observe thin-layer oxide film, or surface oxide formation, consisting of an oxygen and metal overlayer that does not extend into the bulk material, in the region between stable oxygen chemisorptions phases and oxidation of the metal bulk. On some surfaces, such as Ag and Au, these surface oxides are dominant phases for a wide range of experimental conditions. Without direct consideration of these surface oxide configurations the computational study of phase behavior for the oxygen adsorption system remains incomplete.

Utilizing Density Functional Theory (DFT) we calculate surface energies for a variety of surface oxide configurations on the Ag, Au, Pd, and Pt (111) surfaces. We demonstrate that the surface energies for these systems can be correlated between similar configurations in a manner similar to adsorption energies of simple atomic adsorbates on the same systems. The nature of these correlations may be approached by considering it a combination of two correlations, the first a correlation for the ?roughening? of the metal surface through the addition of metal atoms from the bulk reservoir, and another correlation for the ?adsorption? of oxygen on the roughened surfaces. Additionally the surface oxide configurations are added to the previous study of phase behavior that included only chemisorbed configurations, to allow for a more complete comparison to experimental results.