Effect of Hubbard U on the construction of low energy Hamiltonians for LaMnO_3 via maximally localized Wannier functions

TL;DR

This study constructs low-energy Hamiltonians for LaMnO_3 using maximally localized Wannier functions, comparing models with different orbital bases and analyzing the influence of the Hubbard U parameter on the resulting tight-binding parameters.

Contribution

It provides a detailed comparison of d-p and e_g Wannier-based models for LaMnO_3, highlighting how the Hubbard U affects the tight-binding parameters in each case.

Findings

TB parameters in the d-p model are U-independent

Effective e_g model TB parameters strongly depend on U

Jahn-Teller distortion effects are established in the d-p model

Abstract

We use maximally localized Wannier functions to construct tight-binding (TB) parameterizations for the e_g bands of LaMnO_3 based on first principles electronic structure calculations. We compare two different ways to represent the relevant bands around the Fermi level: i) a d-p model that includes atomic-like orbitals corresponding to both Mn(d) and O(p) states in the TB basis, and ii) an effective e_g model that includes only two e_g-like Wannier functions per Mn site. We first establish the effect of the Jahn-Teller distortion within the d-p model, and then compare the TB representations for both models obtained from GGA+U calculations with different values of the Hubbard parameter U. We find that in the case of the d-p model the TB parameters are rather independent on the specific value of U, if compared with the mean-field approximation of an appropriate multi-band Hubbard Hamiltonian. In contrast, the U dependence of the TB parameters for the effective e_g model cannot easily be related to a corresponding mean-field Hubbard model, and therefore these parameters depend critically on the specific value of U, and more generally on the specific exchange-correlation functional, used in the electronic structure calculation.