Oxygen and vacancies in silver: A density-functional study in the local density and generalized gradient approximations

The insertion of oxygen atoms in silver and their interaction with vacancies are studied with density-functional theory calculations using a plane wave basis set. Oxygen atoms are found to be preferentially inserted in octahedral interstitial sites and to have strong interactions with monovacancies as well as with divacancies. An original configuration is evidenced for the oxygen-divacancy complex where the oxygen atom is located halfway between the two nearest-neighbor vacancies, whereas the oxygen-vacancy pair reduces in fact to an oxygen atom in the available substitution site. Quantitative estimates of the formation energies of silver mono- and divacancies, solution energies of oxygen in various sites, and binding energies of oxygen with one or two vacancies are calculated either with local density or generalized gradient approximations. Both functionals lead to the same qualitative results but the calculated energies differ significantly. It is not possible to conclude, from comparison with available experiments, which functional is the most accurate.