Revisiting LaMnO₃: A density functional theory study

Density functional theory has been widely applied to a variety of realistic materials but often fails to accurately describe the properties of correlated systems. The DFT + U method, which introduces a Hubbard U correction to the DFT, has been instrumental in the study of systems such as transition metal oxides. However, the methodological details of DFT + U and its specific impact on the electronic structure and magnetic properties of correlated systems remain incompletely understood. In this study, using the prototypical transition metal oxide LaMnO₃ as an example, we systematically assess the performance of two distinct DFT + U methods: spin-polarized DFT + U (SDFT + U) and spin-unpolarized charge-only DFT + U (CDFT + U). We found that, while the Coulomb U acts similarly in both approaches, the Hund's J_H plays a fundamentally different role, particularly in determining the correct magnetic phases. Our investigation demonstrates the active role of J_H in the exchange splitting, leading to distinct magnetic ground states based on the different schemes. We further investigate the associated magnetic exchange interactions and compare our results with beyond-DFT methods.