Computing the phononic properties of the metal-insulator transition in LuNiO₃

The rare earth nickelates (RNiO₃) undergo a novel metal-insulator transition dubbed the site selective Mott transition. While the electronic picture of this phase transition has been extensively studied, the vibrational properties have not been explored due to the associated complexity. Here, we present the first step in understanding and predicting the structural disproportionation transition in the rare earth nickelates. The efficient bundled irreducible derivative approach was used to compute the phonons of LuNiO₃ in both the Pbnm and P2₁/c phases within DFT+U as a function of the Hubbard U, and comparisons with the experimental Raman spectra are provided. Additionally, we present the energy landscape of the bond disproportionation distortion as a function of U. An estimate of the transition temperature is provided based on the anharmonic phonon free energy within the independent mode approximation.