Influence of nickel(II) oxide surface magnetism on molecule adsorption: A first-principles study

The influence of the magnetism of transition metal oxide, nickel(II) oxide (NiO), on its surface reactivity and the dependence of surface reactivity on surface orientation and reactant magnetism were studied by density functional theory plus U calculations. We considered five different antiferro-magnetically ordered structures and one ferromagnetically ordered structure, NiO(001) and Ni(011) surfaces, paramagnetic molecule NO, and nonparamagnetic molecule CO. The calculations showed that the dependence of surface energies on magnetism was modest, ranging from 49 to 54 meV/angstrom(2) for NiO(001) and from 162 to 172 meV/angstrom(2) for NiO(011). On NiO(001), both molecules preferred the top site of the Ni cation exclusively for all NiO magnetic structures considered, and calculated adsorption energies ranged from -0.33 to -0.37 eV for CO and from -0.42 to -0.46 eV for NO. On NiO(011), both molecules preferred the bridge site of two Ni cations irrespective of the NiO magnetism. It was found that rather than the long-range magnetism of bulk NiO, the local magnetic order of two coordinated Ni cations binding to the adsorbed molecule had a pronounced influence on adsorption. The calculated NO adsorption energy at the (up down arrow.) bridge sites ranged from -0.99 to -1.05 eV, and become stronger at the (up arrow up arrow) bridge sites with values of -1.21 to -1.30 eV. For CO, although the calculated adsorption energies at the (up down arrow) bridge sites (-0.73 to -0.75 eV) were very close to those at the (up arrow up arrow) bridge sites (-0.71 to -0.72 eV), their electron hybridizations were very different. The present work highlights the importance of the local magnetic order of transition metal oxides on molecular adsorption at multi-fold sites. (C) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved