Researchers from the École Polytechnique Fédérale de Lausanne (EPFL), including Yihan Wu, Mario Caserta, Tommaso Chiarotti, and Nicola Marzari, have made significant strides in understanding the electronic structure and dynamical correlations in antiferromagnetic BiFeO3, a material known for its multiferroic properties at room temperature. Their work, published in the journal Physical Review Letters, offers insights that could have practical applications in the energy sector, particularly in the development of advanced materials for energy storage and conversion devices.
The team focused on the electronic structure of BiFeO3, a material that exhibits both magnetic and electric ordering. Using a variety of static and dynamical first-principles methods, they addressed a long-standing issue in the field: the incorrect prediction of a deep-valence Fe 3d peak around -7 eV in antiferromagnetic BiFeO3 by conventional static Hubbard corrections (DFT+U, DFT+U+V). This discrepancy with experimental data from hard-X-ray photoemission spectroscopy (HAXPES) has been a challenge for researchers.
To resolve this issue, the researchers employed a more advanced approach called DFT+U(ω), which includes a frequency-dependent screening. This method, along with a dynamical Hubbard functional (dynH), provided a more accurate description of the material’s electronic structure. The screened Coulomb interaction U(ω), computed with spin-polarized Random Phase Approximation (RPA) and projected onto maximally localized Fe 3d Wannier orbitals, was expressed as a sum-over-poles, yielding a self-energy that augments the Kohn-Sham Hamiltonian.
The DFT+U(ω) approach predicted a fundamental band gap of 1.53 eV, consistent with experimental observations, and eliminated the unphysical deep-valence peak. The resulting simulated HAXPES spectrum closely matched the experimental lineshape, demonstrating the accuracy and efficiency of the DFT+U(ω) method.
For the energy industry, this research highlights the importance of understanding and accurately modeling the electronic structure of complex oxides. These materials have potential applications in energy storage, conversion, and other advanced technologies. The DFT+U(ω) method offers a computationally efficient way to predict the properties of correlated materials, which could accelerate the development of new materials for energy-related applications.
The research was published in Physical Review Letters, a prestigious journal in the field of physics. This work not only resolves a long-standing issue in the study of BiFeO3 but also establishes DFT+U(ω) as a powerful tool for future research in correlated materials.
This article is based on research available at arXiv.