Density functional theory study of H, C and O chemisorption on UN (001) and (111) surfaces

We performed density functional theory calculations of H, C, and O chemisorption on the UN (001) and (111) surfaces using the generalized gradient approximation (GGA) and the Hubbard U parameter and revised Perdew-Burke-Ernzerhof (RPBE) exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. distance of molecules from UN (001) and UN (111) surfaces have been optimized for four symmetrical chemisorption sites, respectively. The results show that the Hollow, N-top, and Hollow adsorption sites are the most stable sites for H, C, and O atoms with chemisorption energies of 13.06, 25.50 and 27.34 kJ/mol for UN (001) surface, respectively. From the point of adsorbent (UN (001) and UN (111) surfaces in this paper), interaction of O with the chemisorbed surface is of the maximum magnitude, then C and H, which are in agreement with electronegativities of individual atoms. For the UN (001) surface, U-N bond lengths change relatively little (< 9%) as a result of H chemisorption, however C and O chemisorptions result in remarkable changes for U-N bond lengths in interlayer (> 10%). Electronic structure calculations indicate that Bridge position is equivalent with Hollow position, and the most stable chemisorption position for H, C, and O atoms are all Bridge (or Hollow) position for the UN (111) surface. Calculated electronic density of states (DOSs) demonstrate electronic charge transfer between s, p orbitals in chemisorbed atoms and U 6d, 5f orbitals. (authors)