Density functional study of CO and NO adsorption on Ni-doped MgO(100).

The adsorption of small molecules such as NO or CO on surfaces of magnetic oxides containing transition metals is difficult to model by current density functional approximations. Two such oxides are NiO(100) and Ni-doped MgO(100). Here we compare the results of a theoretical model of the Ni-doped MgO(100) surface with experimental results on NiO(100), which introduces some uncertainty into a quantitative theory-experiment comparison. In the present work, we tested seven meta-GGA and hybrid metafunctionals, in particular, three developed by the Minnesota group (M05, M06-L, and M06), and TPSS, TPSSh, TPSSKCIS, and B1B95; six GGA functionals, including BP86, PBE, and four other functionals that are modifications of PBE (PBEsol, SOGGA, revPBE, and RPBE); five hybrid GGA functionals (B3LYP, PBE0, B97-2, B97-3, and MPWLYP1M); and one unconventional functional of the generalized gradient type with scaled correlation called MOHLYP. The Minnesota meta-GGA functionals were found in the past to be very good choices when transition metal atoms were present; the other functionals chosen are a selection from the most currently used and most promising sets of functionals for bulk solids and surfaces and for transition metals. The difficulty is due to the charge transfer between open shells in the case of NO and to the weak character of the interaction in the case of CO. It is shown that the M06 hybrid meta functional applied to NO or CO on a model of the Ni-doped MgO(100) surface is able to provide a good description of both adsorbate geometries and binding energies. The M06 vibrational frequency shifts are more accurate than for other functionals, but there is still room for improvement.