Structures and energetics of H2O adsorption on the Fe3O4 (111) surface

Water adsorption on the Fetet1-terminated and Feoct2-terminated surfaces of Fe3O4(111) has been calculated at the level of density functional theory (GGA/PBE). On the Fetet1-terminated surface at 1/5 monolayer (ML), the molecular adsorption mode with a hydrogen bond and the heterolytically dissociative mode show the highest stability, whereas the hydronium-ion-like structure OH3+-OH becomes possible at 2/5 ML, followed by the hydrogen-bonded water aggregate. These results agree well with the available experimental observations. For Feoct2-terminated surface, the molecular water prefers to adsorb on the surface Feoct2 atom at 1/6 ML, whereas other adsorption modes become possible and may coexist at 1/3 ML. The Fetet1-terminated surface is more favorable than the Feoct2-terminated surface for water adsorption. The adsorption mechanism has been analyzed on the basis of the calculated local density of state.