  We present and discuss the results of ab initio DFT plane-wave supercell
calculations of the atomic and molecular oxygen adsorption and diffusion on the
LaMnO3 (001) surface which serves as a model material for a cathode of solid
oxide fuel cells. The dissociative adsorption of O2 molecules from the gas
phase is energetically favorable on surface Mn ions even on a defect-free
surface. The surface migration energy for adsorbed O ions is found to be quite
high, 1.6 eV. We predict that the adsorbed O atoms could penetrate into
electrode first plane when much more mobile surface oxygen vacancies (migration
energy of 0.69 eV) approach the O ions strongly bound to the surface Mn ions.
Ab initio thermodynamics predicts that at typical SOFC operation temperatures
(~1200 K) the MnO2 (001) surface with adsorbed O atoms is the most stable in a
very wide range of oxygen gas pressures (above 10^2 atm).
