Multiplet effects in the electronic correlation of one-dimensional magnetic transition metal oxides on metals

We use the constrained random-phase approximation (cRPA) method to calculate the Hubbard U parameter in four one-dimensional magnetic transition metal atom oxides of composition XO2 (X = Mn, Fe, Co, Ni) on Ir(100). In addition to the expected screening of the oxide, i.e., a significant reduction of the U value by the presence of the metal substrate, we find a strong dependence on the electronic configuration (multiplet) of the X(d) orbital. Each particular electronic configuration attained by atom Xis dictated by the O ligands, as well as by the charge transfer and hybridization with the Ir(100) substrate. We find that MnO2 and NiO2 chains exhibit two different screening regimes, while the case of CoO2 is somewhere in between. The electronic structure of the MnO2 chain remains almost unchanged upon adsorption. Therefore, in this regime, the additional screening is predominantly generated by the electrons of the neighboring metal surface atoms. The screening strength for NiO2/Ir(100) is found to depend on the Ni(d) configuration in the adsorbed state. The case of FeO2 shows an exceptional behavior, as it is the only insulating system in the absence of the metallic substrate and, thus, it has the largest U value. However, this value is significantly reduced by the two mentioned screening effects after adsorption.