Adsorption of atomic oxygen on HfC and TaC (1 1 0) surface from first principles

We investigated the initial adsorption of oxygen atom on the HfC (1 1 0) and TaC (1 1 0) surface using first principles. Both the carbides have the same crystal structure, a sodium–chloride structure. The (1 1 0) surfaces of the carbides were modeled with (2 × 1) supercells. Every supercell is composed of five atomic planes. Our results demonstrate that the preferred site for oxygen atom is the C–Hf bridge site and the Ta–Ta bridge site on the HfC (1 1 0) and TaC (1 1 0) surface, respectively. The adsorption sites are different from the one on the (1 0 0) surfaces of the carbides. For the carbides, the adsorption energies of oxygen on the (1 1 0) surfaces are larger than that on the (1 0 0) surfaces. There exists the Csingle bondO bond in O/HfC (1 1 0), while no Csingle bondO bond is found in O/TaC (1 1 0), indicating that the adsorption mechanism of atomic oxygen on the TaC (1 1 0) surface is different from that on the HfC (1 1 0) surface at initial adsorption stage.