  Fabrication, handling and disposal of nuclear fuel materials require
comprehensive knowledge of their surface morphology and reactivity. Due to
unavoidable contact with air components (even at low partial pressures), UN
samples contain considerable amount of oxygen impurities affecting fuel
properties. The basic properties of O atoms adsorbed on the UN(001) surface are
simulated here combining the two first principles calculation methods based on
the plane wave basis set and that of the localized atomic orbitals.
