Hubbard-U-corrected electron-phonon interactions in strongly correlated materials via the finite-displacement method

Summary

This paper combines density functional theory with the Hubbard U correction (DFT+U) and the finite displacement method to achieve a full Hubbard-corrected calculation of phonon spectra and electron-phonon matrices in strongly correlated materials. The authors apply this method to two representative systems: infinite-layer nickelate LaNiO₂ and ruthenium dioxide RuO₂. The results show that in 20% hole-doped LaNiO₂, the Hubbard U correction weakly enhances the electron-phonon interaction, but the total coupling strength remains small and insufficient to explain the experimentally observed superconducting transition temperature of approximately 10–30 K; this contradicts recent predictions from the GW correction, with the discrepancy arising from differences in the Fermi surface topology obtained by DFT+U and GW methods. In RuO₂, the Hubbard U correction eliminates imaginary phonon modes under TiO₂ substrate strain and significantly reduces the electron-phonon coupling, alleviating the contradiction between the theoretically overestimated electron-phonon coupling and the experimentally observed low superconducting transition temperature. This work provides a computational scheme that fully incorporates the Hubbard U correction for electron-phonon properties and highlights the critical influence of Fermi surface shape and correlation effects on phonon spectra and electron-phonon matrices.

Materials

• LaNiO₂
• RuO₂

Methods

• DFT+U
• finite-displacement method
• electron-phonon coupling calculations

Keywords

• electron phonon coupling
• hubbard u correction
• phonon hardening
• fermi surface topology

Highlights

• Implements a fully self-consistent Hubbard-U correction to electron-phonon calculations using the finite-displacement method.
• Shows that partially corrected approaches (corrections only to electronic structure) can be qualitatively incorrect.
• Highlights the importance of Fermi surface shape and correlation effects on phonon spectra and electron-phonon matrices.

Conclusions

• For 20% hole-doped LaNiO₂, Hubbard U corrections weakly increase electron-phonon coupling, but the total coupling remains too small to explain the observed T_c of 10-30 K.
• The discrepancy between DFT+U and GW methods is attributed to differences in Fermi surface topology.
• For TiO₂-strained RuO₂, Hubbard U corrections eliminate imaginary phonon modes and substantially reduce electron-phonon coupling, alleviating the discrepancy between theory and experiment.
• Correlation effects modify electron-phonon coupling through both electronic (Fermi surface) and phonon (hardening) channels.

Main claims

• Hubbard U corrections weakly increase electron-phonon coupling in LaNiO₂ but remain insufficient to explain observed T_c
  • Evidence: From abstract: 'the Hubbard U corrections weakly increase the electron-phonon interaction of 20% hole-doped LaNiO₂, its total electron-phonon coupling remains small and is insufficient to account for the observed superconducting transition temperature of about 10-30 K'
• In RuO₂, Hubbard U corrections eliminate imaginary phonon modes and substantially reduce electron-phonon coupling, resolving discrepancy with experimental T_c
  • Evidence: From abstract: 'The inclusion of Hubbard U corrections eliminates the imaginary phonon modes of RuO₂ under strain on the TiO₂ substrate and substantially reduces the electron-phonon coupling. Our results alleviate the discrepancy between the reported large theoretical electron-phonon coupling and the low superconducting transition temperature observed experimentally'

Workflow

• algorithm_implementation — Full Hubbard-U corrections implemented in electron-phonon calculations
  • Materials: DFT+U framework; finite-displacement method
  • Methods: integration of DFT+U with finite-displacement for phonons and e-ph matrices
  • Observations: phonon spectra; electron-phonon coupling
• application_to_LaNiO2 — Hubbard corrections weakly increase e-ph coupling but remain insufficient for observed T_c
  • Materials: 20% hole-doped LaNiO₂
  • Methods: DFT+U with finite-displacement
  • Observations: band structure; Fermi surface; electron-phonon coupling
• application_to_RuO2 — Hubbard corrections eliminate imaginary phonon modes and reduce e-ph coupling
  • Materials: TiO₂-strained RuO₂
  • Methods: DFT+U with finite-displacement
  • Observations: phonon stability; electron-phonon coupling