Understanding the role of Hubbard corrections in the rhombohedral phase of BaTiO3

We present a first-principles study of the low-temperature rhombohedral phase of BaTiO3 using Hubbard-corrected density-functional theory. By employing density-functional perturbation theory, we compute the onsite Hubbard 𝑈 for Ti⁡(3⁢𝑑) states and the intersite Hubbard 𝑉 between Ti⁡(3⁢𝑑) and O⁡(2⁢𝑝) states. We show that applying the onsite Hubbard 𝑈 correction alone to Ti⁡(3⁢𝑑) states proves detrimental, as it suppresses the Ti⁡(3⁢𝑑)–O⁡(2⁢𝑝) hybridization and drives the system towards a cubic phase. Conversely, when both onsite 𝑈 and intersite 𝑉 are considered, the localized character of the Ti⁡(3⁢𝑑) states is maintained, while also preserving the Ti⁡(3⁢𝑑)–O⁡(2⁢𝑝) hybridization, restoring the rhombohedral phase of BaTiO3. The generalized PBEsol+𝑈 +𝑉 functional yields good agreement with experimental results for the band gap and dielectric constant, while the optimized geometry is slightly less accurate compared to PBEsol. Zone-center phonon frequencies and Raman spectra are found to be significantly influenced by the underlying geometry. PBEsol and PBEsol+𝑈 +𝑉 provide satisfactory agreement with the experimental Raman spectrum when the PBEsol geometry is used, while PBEsol+𝑈 Raman spectrum diverges strongly from experimental data highlighting the adverse impact of the 𝑈 correction alone in BaTiO3. Our findings underscore the promise of the extended Hubbard PBEsol+𝑈 +𝑉 functional with first-principles 𝑈 and 𝑉 for the investigation of other ferroelectric perovskites with mixed ionic-covalent interactions.

Recommended citation: G. Gebreyesus, L. Bastonero, M. Kotiuga, N. Marzari, and I. Timrov, Understanding the role of Hubbard corrections in the rhombohedral phase of BaTiO3, Phys. Rev. B 108, 235171 (2023)
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