Magnetic and f-electron effects in LaNiO2 and NdNiO2 nickelates with cuprate-like 3d(x2-y2) band

Recent discovery of superconductivity in the doped infinite-layer nickelates has renewed interest in understanding the nature of high-temperature superconductivity more generally. The low-energy electronic structure of the parent compound NdNiO2, the role of electronic correlations in driving superconductivity, and the possible relationship between the cuprates and the nickelates are still open questions. Here, by comparing LaNiO2 and NdNiO2 systematically within a parameter-free, all-electron first-principles density-functional theory framework, we reveal the role of Nd 4f electrons in shaping the ground state of pristine NdNiO2. Strong similarities are found between the electronic structures of LaNiO2 and NdNiO2, except for the effects of the 4f electrons. Hybridization between the Nd 4f and Ni 3d orbitals is shown to significantly modify the Fermi surfaces of various magnetic states. In contrast, the competition between the magnetically ordered phases depends mainly on the gaps in the Ni 3d(x2-y2) band. Our estimated value of the on-site Hubbard U in the nickelates is similar to that in the cuprates, but the value of the Hund's coupling J(H) is found to be sensitive to the Nd magnetic moment. In contrast with the cuprates, NdNiO2 presents 3D magnetism with competing antiferromagnetic and (interlayer) ferromagnetic exchange, which may explain why the T-c is lower in the nickelates.