Effect of off-diagonal elements in the Wannier Hamiltonian on DFT plus DMFT for low-symmetry materials: Study of Li2MnO3

We study the effect of the off-diagonal elements of the Wannier Hamiltonian on the electronic structure of the low-symmetry material Li2MnO3 (C2/m), using dynamical mean field theory calculations with a continuous-time quantum Monte Carlo impurity solver. The presence of significant off-diagonal elements leads to a pronounced suppression of the energy gap. The off-diagonal elements are largest when the Wannier projection is used based on the global coordinate, and they remain substantial even with the projection using the local coordinate close to the direction of Mn-O bonds. We show that the energy gap is enhanced by the diagonalization of the Mn d block in the full p -d Hamiltonian with the application of a unitary rotation matrix. Additionally, the inclusion of small double counting energy is crucial for achieving the experimental gap by reducing p -d hybridization. Furthermore, we establish the efficiency of a low-energy (d-only basis) model for studying the electronic structure of Li2MnO3, as the Wannier basis represents a hybridized state of Mn d and O p orbitals. These findings suggest an appropriate approach for investigating low-symmetry materials using the density functional theory plus dynamical mean field theory (DFT + DMFT) method. We also find that the antiferromagnetic ground state I'2u is stable with U 2 eV within density functional theory+U calculations, which is much smaller than the widely used U = 5 eV.

Automated summary

This study investigates the impact of the off-diagonal elements of the Wannier Hamiltonian on the electronic structure of Li2MnO3 using dynamical mean field theory calculations. The presence of these elements significantly reduces the energy gap, even when using local coordinates. By diagonalizing the Mn d block and applying a rotation matrix, the energy gap can be enhanced. Additionally, considering the small double counting energy is crucial for reducing p-d hybridization to achieve the experimental energy gap. This study also suggests the effectiveness of using the density functional theory plus dynamical mean field theory method to investigate low-symmetry materials.