  The density functional theory (DFT) is used in a study of point defects on
both UN (001) surface and sub-surface layers. We compare results for slabs of
different thicknesses (both perfect and containing nitrogen or uranium
vacancies) with a full geometry, electronic and spin density optimization. The
electronic charge density re-distribution, density of states, magnetic moments
of atoms as well as local atomic displacements around defects are carefully
analyzed. It is predicted that the vacancies are formed easier on the surface
whereas the sub-surface layer does not differ signifincantly from the central
one in the slab.
