Adsorption of nitrogen atom on the (001) surface of HfC and TaC: A first-principles study

First-principles calculations are performed to investigate the adsorption of nitrogen atom on the HfC and TaC (0 0 1) surface. The (√2 × √2) R45° supercell slabs are employed to calculate the adsorption at 0.5 monolayer coverage. In our calculations, the exchange-correlation potential is treated with the revised version of the Perdew-Burke-Ernzerhof (RPBE) functional. Our results show that the adsorption of N atom is a large exothermic process, indicating the interactions between N atom and the (0 0 1) surfaces are strong. The preferred adsorption site of N atom is MMC (M = Hf or Ta) site on the (0 0 1) surfaces. The results from Mulliken charges, bond population and density of states (DOS) demonstrate that N–C bonds in N/HfC (0 0 1) has more covalent characters than that in N/TaC(001). Meanwhile, N–Ta bond exhibits more covalent characters than N–Hf bond. Compared with the interactions of O atom and the (0 0 1) surfaces, the covalent interaction of N atom and the HfC (0 0 1) surface is weak, while the interaction between N atom and the TaC (0 0 1) surface is strong. Our results may provide basic information intended as a reference for the further development of HfC and TaC thermal protection materials.