Effect of Off-Diagonal Elements in Wannier Hamiltonian on DFT+DMFT for low symmetry material Li₂MnO₃

We investigate the impact of the Wannier Hamiltonian's off-diagonal elements on the electronic structure of Li₂MnO₃ (C2/m) employing dynamical mean field theory (DMFT) and continuous-time Quantum Monte Carlo. These elements significantly narrow the energy gap, more so with global-coordinate-based Wannier projection; this remains true even with local coordinate projection. The energy gap widens upon diagonalizing the Mn d block in the p-d Hamiltonian via a unitary rotation matrix. Importantly, incorporating minimal double counting energy is crucial to achieving the experimental gap by diminishing p-d hybridization. Our study demonstrates that a d-only low-energy model efficiently probes the electronic structure of Li₂MnO₃, with the Wannier basis signifying a hybridized state of Mn d and O p orbitals. These insights offer a refined methodology for exploring low-symmetry materials using DFT+DMFT. Furthermore, our magnetic stability investigation through DFT+U uncovers the Γ_2u antiferromagnetic ground state at U ≤ 2 eV, in contrast to the more stable Γ_3g state at the prevalent U = 5 eV. These observations necessitate a reevaluation of interaction parameters in analogous materials.