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 x 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 C-O bond in O/HfC (1 1 0), while no C-O 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. (C) 2012 Elsevier B. V. All rights reserved.