Calculation of model Hamiltonian parameters forLaMnO3using maximally localized Wannier functions

Abstract

Maximally localized Wannier functions (MLWFs) based on Kohn-Sham band-structures provide a systematic way to construct realistic, materials specific tight-binding models for further theoretical analysis. Here, we construct MLWFs for the Mn eg bands in LaMnO3, and we monitor changes in the MLWF matrix elements induced by different magnetic configurations and structural distortions. From this we obtain values for the local Jahn-Teller and Hund's rule coupling strength, the hopping amplitudes between all nearest and further neighbors, and the corresponding reduction due to the GdFeO3-type distortion. By comparing our results with commonly used model Hamiltonians for manganites, where electrons can hop between two "eg-like" orbitals located on each Mn site, we find that the most crucial limitation of such models stems from neglecting changes in the underlying Mn(d)-O(p) hybridization.

Maximally localized Wannier functions in LaMnO3within PBE +U, hybrid functionals and partially self-consistent GW: an efficient route to constructab initiotight-binding parameters for egperovskites

“…The hopping amplitude t ↑↓ between A-AFM ordered planes is then calculated as average of t ↑↑ and t ↓↓ . As also shown in [31], the JT distortion induces a strong splitting between the nondiagonal elements of the nearest-neighbor hopping matrix within the xy plane (see the differences between h figure 8(a,b)), which is parameterized via a non-local JT coupling strength λ (see (1.5) in Appendix).…”

“…[9] have been used. The JT coupling parameters differ slightly more from [31], due to the revised definition of λ s used in Figure 8. Hamiltonian matrix elements in the basis of MLWFs for the experimental P bnm structure: nearest-neighbor terms corresponding to local majority (a) and minority (b) spin projection, diagonal (c) and off-diagonal (d) on-site terms.…”

“…Another important change arises from the use of 3 separate GFO reduction factors η ↑ t , η ↓ t , and η λ , instead of using one averaged value as it was done in [31]), which provides a more accurate TB description of the MLWF bands. It can be also seen from table 3 that at the PBE level, there is essentially no difference between the hopping amplitudes calculated using PWscf and VASP.…”

“…often achieved by downfolding the relevant bands and constructing a localized Wannier basis [29,13,30,31,32].…”

“…Some of the authors have recently shown that maximally localized Wannier functions (MLWFs) can be used to extract an effective TB description of the e g subspace in LaMnO 3 [31,32]. The calculated TB parameters can then be used to construct a simplified TB Hamiltonian in the form that is very often used for the description of manganites,Ĥ TB =Ĥ kin +Ĥ Hund +Ĥ JT +Ĥ e−e , which then provides a very accurate representation of the underlying Kohn-Sham band structure.…”