DFT+U study of the surface structure and stability of Co₃O₄(110): Dependence on U

The (110) surface of tricobalt tetraoxide, Co₃O₄(110), has attracted considerable interest because of its high catalytic activity, especially for CO oxidation. However, understanding of its surface structure and reactivity under relevant experimental conditions remains limited. Here, we use density functional theory with the on-site Coulomb U term to study the structure and stability of the two possible truncations of Co₃O₄(110) in the presence of oxygen gas and water vapor. We examine the effects of U on the stability diagram by considering three representative U values often used in previous studies, notably U = 0, 3.0, and 5.9 eV. For all U values, the hydrated B surface, exposing only octahedral Co ions, is predicted to be the thermodynamically stable termination under ambient conditions and at low temperatures. In other situations, the predicted stability generally depends on U with smaller (larger) U values favoring the B (A) termination. By combining our results with those of previous studies, we conclude that U = 3.0 eV provides a better overall description of the electronic structure and surface reactivity, whereas U = 5.9 eV is better suited for description of the magnetic properties.