Structural, electronic, and magnetic properties of the CrN (0 0 1) surface: First-principles studies

Spin-polarized, first-principles total energy calculations have been performed to investigate the structural, electronic and magnetic properties of the chromium nitride (0 0 1) surface. Different approximations were used to treat the non-classical exchange correlation energy: LDA, GGA, LDA + U (3 eV ≤ U ≤ 5 eV) and GGA + U (1 eV ≤ U ≤ 4 eV). It was found that LDA + U with U = 4 eV describes correctly the structural, electronic and magnetic properties of bulk CrN. The CrN (0 0 1) surface has been investigated, employing the surface formation energy (SFE) formalism. For the surface in the cubic phase, three different structures were found to be stable: an ideally terminated surface, one with no nitrogen atoms in the second layer, and one with half of the nitrogen atoms missing in the second layer. In the case of the orthorhombic surface, only the ideal surface is stable in all the range of the chemical potential. Density of States (DOS) calculations show a metallic behavior for all the stable surface structures, with the main contribution around the Fermi level coming from Cr-d orbitals. The effect of nitrogen vacancies is clearly observed with an increase in the metallic behavior in the structures having less nitrogen atoms.