Modelling the electronic structure and magnetic properties of LiFeAs and FeSe using hybrid-exchange density functional theory

Abstract

The electronic structure and magnetic properties of LiFeAs and FeSe have been studied using hybrid exchange density functional theory. The total energies for a unit cell in LiFeAs and FeSe with different spin states including non-magnetic and spin-2 are calculated. The spin-2 configuration has the lower energy for both LiFeAs and FeSe. The computed anti-ferromagnetic exchange interactions between spins on the nearest (next nearest) neighbouring Fe atoms in LiFeAs and FeSe are approximately 14 (17) meV and 6 (13) meV respectively. The total energies of the checkerboard and stripe-type anti-ferromagnetic ordering for LiFeAs and FeSe are compared, yielding that for LiFeAs the checkerboard is lower whereas for FeSe the stripe-type is lower. However, owing to the fact that the exchange interaction of the next nearest neighbour is larger than that of the nearest one, which means that the collinear ordering might be the ground state. These results are in agreement with previous theoretical calculations and experiments. Especially the calculations for LiFeAs indicate a co-existence of conducting d-bands at the Fermi surface and d-orbital magnetism far below the Fermi surface. The theoretical results presented here might be useful for the experimentalists working on the electronic structure and magnetism of ironbased superconductors.

Competing collinear magnetic structures in superconducting FeSe by first-principles quantum Monte Carlo calculations

“…It appears that hybrid DFT calculations in the PBE0 approximation obtain reasonably good magnetic energy differences in comparison to DMC; since this functional also produced the orbitals that gave the lowest FN-DMC energy, it may be capturing some of the correct physics for the magnetic properties of this material. However, the PBE0 functional predicts an insulating gap in agreement with previous work [47] for FeSe for all magnetic orderings, in contrast to DMC and experiment.…”

Electronic Structure of β-NaxV2O5 (x ≈ 0.33) Polycrystalline Films: Growth, Spectroscopy, and Theory

“…44 The performance of the hybrid-exchange functional such as PBE0, implemented in CRYSTAL code, 46 has previously been shown to provide an accurate description of the electronic structure and magnetic properties for both inorganic and organic compounds. 50,51 ■ RESULTS AND DISCUSSION I. Hard X-ray Photoelectron Spectroscopy.…”

“…The advantages of hybrid-exchange functional include a partial elimination of the self-interaction error and balancing the tendencies to delocalize and localize wave functions by mixing a quarter of Fock exchange with that from a generalized gradient approximation (GGA) exchange functional . The performance of the hybrid-exchange functional such as PBE0, implemented in CRYSTAL code, has previously been shown to provide an accurate description of the electronic structure and magnetic properties for both inorganic and organic compounds. , …”

Electronic Structure of FeSe1–xTex Studied by X-ray Spectroscopy and Density Functional Theory

“…The theoretical considerations carried out by Ma et al 5 presumed that FeTe is in a bicollinear antiferromagnetic order while FeSe is in a collinear antiferromagnetic one. Recent calculations 44 on the magnetic ordering of FeSe using hybrid-exchange DFT showed that nonmagnetic order has higher ground state energy than the magnetic one, although temperature and pressure variations as well as lattice distortions (as those taking place in FeSe 1−x Te x ) could drive the material into different magnetic regimes. Using polarized Raman-scattering techniques, very recent experiments 45,46 showed that FeSe and FeTe undergo spin fluctuations as a function of temperature; manifesting higher spin states at high temperatures and driving FeSe (FeTe) from ferromagnetic (antiferromagnetic) to paramagnetic as the temperature increases.…”