[Paper Review] Lattice normal modes and electronic properties of the correlated metal LaNiO$_3$

Gaoyang Gou, Ilya Grinberg+2 more|arXiv (Cornell University)|May 1, 2011

Magnetic and transport properties of perovskites and related materials3 citations

TL;DR

This study uses density functional theory (DFT) to investigate lattice vibrations and electronic structure in the correlated metal LaNiO₃. It demonstrates that strong Ni 3d–O 2p hybridization enhances electronic screening, reducing electron correlations and stabilizing the metallic state; conventional LSDA provides the best agreement with experiment for both electronic and lattice dynamics, while the A₁g Raman mode serves as a sensitive probe of octahedral rotations in the rhombohedral phase.

ABSTRACT

We use density functional theory (DFT) calculations to study the lattice vibrations and electronic properties of the correlated metal LaNiO$_3$. To characterize the rhombohedral to cubic structural phase transition of perovskite LaNiO$_3$, we examine the evolution of the Raman-active phonon modes with temperature. We find that the $A_{1g}$ Raman mode, whose frequency is sensitive to the electronic band structure, is a useful signature to characterize the octahedral rotations in rhombohedral LaNiO$_3$. We also study the importance of electron--electron correlation effects on the atomic structure with two approaches which go beyond the conventional band theory (local spin density approximation): the local spin density+Hubbard $U$ method (LSDA$+U$) and hybrid exchange-correlation density functionals which include portions of exact Fock-exchange. We find the conventional LSDA accurately reproduces the delocalized nature of the valence states in LaNiO$_3$ and gives the best structural and vibrational agreement to the available experimental data. Based on our calculations, we show that the electronic screening effect from the delocalized Ni 3$d$ and O-2$p$ states mitigate the electronic correlations of the $d^7$ Ni cations, making LaNiO$_3$ a weakly correlated metal.

Motivation & Objective

• To understand the interplay between lattice dynamics and electronic correlations in the correlated metal LaNiO₃.
• To determine the role of Ni 3d–O 2p hybridization in mitigating electron–electron correlations and stabilizing the metallic state.
• To evaluate the performance of various DFT functionals—LSDA, LSDA+U, PBE0, and HSE—in describing the electronic and vibrational properties of LaNiO₃.
• To identify a spectroscopic signature (the A₁g Raman mode) for quantifying octahedral rotations in rhombohedral perovskites.
• To assess the limitations of standard DFT functionals in capturing dynamical correlation effects in the Ni e_g states.

Proposed method

• Employed density functional theory (DFT) with the local spin density approximation (LSDA) to compute electronic structure and lattice dynamics of LaNiO₃.
• Applied the LSDA+U method with an orbital-dependent Hubbard U value of 5.74 eV to assess the impact of electron–electron correlations on the Ni 3d states.
• Used hybrid exchange-correlation functionals (PBE0 and HSE) to improve the description of electronic band structure and core-level binding energies.
• Performed linear response calculations to determine the temperature-dependent evolution of Raman-active phonon modes, particularly the A₁g mode.
• Used Landau theory of phase transitions to model the rhombohedral-to-cubic structural transition in LaNiO₃.
• Compared calculated spectroscopic properties (core-level binding energies, valence band structure) with experimental data to validate functional performance.

Experimental results

Research questions

• RQ1 How do lattice vibrations, particularly the A₁g Raman mode, reflect the degree of octahedral rotation in rhombohedral LaNiO₃?
• RQ2 To what extent does Ni 3d–O 2p hybridization reduce effective electron–electron correlations in LaNiO₃?
• RQ3 Which DFT functional—LSDA, LSDA+U, PBE0, or HSE—best reproduces the experimental electronic structure and lattice dynamics of LaNiO₃?
• RQ4 Why does the Ni e_g orbital exhibit enhanced spectral weight at the Fermi level upon cooling, and can this be captured by standard DFT functionals?
• RQ5 What is the role of electronic screening in stabilizing the metallic state in LaNiO₃ despite the presence of d⁷ Ni³⁺ cations?

Key findings

• The A₁g Raman mode, which corresponds to the rotation of adjacent NiO₆ octahedra, serves as a sensitive structural probe for quantifying octahedral rotations in rhombohedral perovskites.
• Conventional LSDA accurately reproduces the delocalized nature of the valence states and shows the best agreement with experimental lattice dynamics and electronic structure in LaNiO₃.
• Strong Ni 3d–O 2p hybridization enhances electronic screening, reducing the effective Coulomb interaction on Ni 3d orbitals and mitigating electron correlation effects.
• The LSDA+U method fails to capture the correct electronic screening and underestimates the delocalization of Ni 3d and O 2p states, leading to poor agreement with experiment.
• Hybrid functionals (PBE0 and HSE) perform best for core-level binding energies but fail to reproduce the correct valence band dispersion and lattice dynamics.
• The dynamical correlation effects in the Ni e_g states, observed experimentally as enhanced spectral weight at the Fermi level, are not captured by LSDA, LSDA+U, or hybrid functionals, indicating a need for dynamical mean-field theory (DMFT) treatments.