Starting from an effective two-dimensional two-band model for infinite-layered nickelates, consisting of bands obtained from d- and s-like orbitals, we investigate to which extent it can be mapped onto a single-band Hubbard model. We identify screening of the more itinerant s-like band as an important driver. In the absence of screening one strongly correlated band gives an antiferromagnetic ground state. For weak screening, the strong correlations push electrons out of the s band so that the undoped nickelate remains a Mott insulator with half-filled d orbitals. This regime markedly differs from the observations in high-Tc cuprates and pairing with s-wave symmetry would rather be expected in the superconducting state. In contrast, for strong screening, the s and dx2-y2 bands are both partly filled and couple only weakly, so that one approximately finds a self-doped d band as well as tendencies toward d-wave pairing. Particularly in the regime of strong screening mapping to a one-band model gives interesting spectral weight transfers when a second s band is also partly filled. We thus find that both one-band physics and a Kondo-lattice-like regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the size of the s-band pocket.
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