The First Principles Study of Strongly Correlated Electronic Structure in Rare-Earth Nickelates

Rare earth nickelates attract numerous interests of research due to their rich physical properties and phase transitions. Here we report the electronic structures of LaNiO3 with oxygen vacancies using first principles. We find that LaNiO2.5 exhibits a ``site-selective" paramagnetic Mott insulating state at T~=290K as obtained using density functional theory plus dynamical mean field theory (DFT+DMFT). The Ni octahedron site develops a Mott insulating state with strong correlations as the Ni eg orbital is half-filled while the Ni square-planar site with apical oxygen vacancies becomes a band insulator. Moreover, we investigate the effects of the surface termination and the oxygen vacancy position on the electronic properties and vacancy energetics of LaNiO3 ultra-thin films under the compressive strain on the LaAlO3 substrate using DFT+U. The existence and positions of oxygen vacancies are found to be very sensitive to the termination of the film. In rare earth nickelates family, the LaNiO2, PrNiO2 and NdNiO2(ReNiO2) were found to be superconductive under hole doping. Their crystal structures have similarities with CaCuO2, which is also a superconductor under field-effect doping with high critical temperature. We also investigate the electronic structures of LaNiO2 and PrNiO2 with hole doping. We calculated the Hubbard U values of Ni 3d and Pr 4f orbitals using constrained DFT method. We found that the hole ions in LaNiO2 do not change the electronic structures and can be approximated by virtual crystal approximation. Doped holes in ReNiO2 partly distribute in Ni 3d orbitals, mainly in dx2-y2 orbitals. The effect of Pr 4f electrons on Ni 3d electrons is negligible, however it has weak effect on Pr 5d electrons at Fermi level.