Lattice normal modes and electronic properties of the correlated metal LaNiO 3

We use density functional theory calculations to study the lattice vibrations and electronic properties of the correlated metal LaNiO3. To characterize the rhombohedral-to-cubic structural phase transition of perovskite LaNiO3, we examine the evolution of the Raman-active phonon modes with temperature. We find that the A1g Raman mode, whose frequency is sensitive to the electronic band structure, is a useful signature to characterize the octahedral rotations in rhombohedral LaNiO3. We also study the importance of electron-electron correlation effects on the electronic structure with two approaches that go beyond the conventional band theory [local spin density approximation (LSDA)]: the local spin density+HubbardU method (LSDA+U) and hybrid exchange-correlation density functionals that include portions of exact Fock exchange. We find that the conventional LSDA accurately reproduces the delocalized nature of the valence states in LaNiO3 and gives the best agreement with the available experimental data on the electronic structure of LaNiO3. Based on our calculations, we show that the electronic screening effect from the delocalized Ni 3d and O-2p states mitigates the electronic correlations of the d7 Ni cations, making LaNiO3 a weakly correlated metal.