Electronic structure of nickelate superconductor NdNiO2Hx (x=0, 0.25, 0.5) under different strains

The discovery of superconductivity in infinite-layer nickelates has drawn considerable attention and boosted numerous theoretical and experimental studies. Here, combining density functional theory and Wannier function calculations, we study the electronic structure of nickelate $\mathrm{NdNi}{\mathrm{O}}_{2}{\mathrm{H}}_{x}$ ($x=0$, 0.25, 0.5) (NNOH) under five different in-plane strains. We unveil that, with H introduced, the orbital occupation of Ni $3{d}_{{x}^{2}\text{\ensuremath{-}}{y}^{2}}$ increases, accompanied by the shift of band structure toward lower energy under constant strain. Meanwhile, the H $1s$ orbital hybridizes and forms a bonding-antibonding state with the Ni $3{d}_{{z}^{2}}$ orbital, reducing the occupation of the Ni $3{d}_{{z}^{2}}$ orbital, which results in the decreased filling of Ni $3d$ orbital. By contrast, the strain has negligible influences on the filling of Ni $3d$ and Ni ${e}_{g}$ orbital polarization. As the H concentration increases, the contribution of the itinerant interstitial $s$ (IIS) orbital to the band structure near the Fermi level gradually decreases and disappears at $x=0.5$ due to the doped H obliterating the IIS band. In addition, with compressive strain applied, the bandwidth of the Ni $3{d}_{{x}^{2}\text{\ensuremath{-}}{y}^{2}}$ orbital increases, consistent with the calculated stronger effective Ni $3{d}_{{x}^{2}\text{\ensuremath{-}}{y}^{2}}$ nearest-neighboring hopping. In addition, we find that the impact of H concentration and strain on the projected orbitals and calculated density of states is slight. Also, the influences of the Sr concentration (0--20%) and Hubbard $U$ parameter on the electronic properties of NNO without strain are explored and found not to change the main conclusions.