Tight-binding Hamiltonian for LaOFeAs

TL;DR

This paper develops a tight-binding Hamiltonian for LaOFeAs that accurately reproduces first-principles band structures, aiding further research into the electronic properties of iron-based superconductors.

Contribution

The authors constructed a transferable tight-binding Hamiltonian from LAPW results, including relevant orbitals, with high accuracy in band structure and Fermi surface reproduction.

Findings

TB model matches LAPW band structure within 3 eV of Fermi level

Fermi surface is accurately reproduced by the TB model

The TB densities of states agree well with LAPW results

Abstract

First-principles electronic structure calculations have been very useful in understanding some of the properties of the new iron-based superconductors. Further explorations of the role of the individual atomic orbitals in explaining various aspects of research in these materials, including experimental work, would benefit from the availability of a tight-binding(TB) Hamiltonian that reproduces accurately the first-principles band structure results. In this work we have used the NRL-TB method to construct a TB Hamiltonian from Linearized Augmented Plane Wave(LAPW) results. Our TB model includes the Fe d-orbitals, and the p-orbitals from both As and O for the prototype material LaOFeAs. The resulting TB band structure agrees well with that of the LAPW calculations in from 2.7 eV below to 0.8 eV above the Fermi level, epsilon_F, and the Fermi surface matches perfectly to that of the LAPW. The TB densities of states(DOS) are also in very good agreement with those from the LAPW in the above energy range, including the per orbital decomposition. We use our results to provide insights on the existence of a pseudogap in the DOS just above the Fermi level. We have also performed a separate TB fit to a database of LAPW results as a function of volume and with variations of the As positions. This fit although less accurate regarding the band structure near epsilon_F, reproduces the LAPW total energies very well and has transferability to non-fitted energies.