Structural, Magnetic, and Electronic Properties of Fe: A Screened Hybrid Functional Study

Abstract

We performed total energy and electronic structure calculations for the basic ground state properties of Fe using the conventional generalized gradient approximation (GGA) and screened hybrid functionals as the form of the exchange-correlation functional. To that end, we calculated structural (equilibrium lattice constants, bulk moduli, and cohesive energies) and electronic (magnetic moments and densities of states) properties. Both functional calculations gave the correct ground state, the ferromagnetic bcc phase, in which the structural parameters agreed well with experimental results. However, the description of the cohesive energies and magnetic moments at the ground state exhibited different behavior from each other: the unusually small cohesive energy and large magnetic moment were observed in the screened hybrid functional calculations compared to the GGA calculations. The reason for the difference was examined by analyzing the calculated electronic structures.

Theoretical investigation into the possibility of very large moments in Fe16N2

“…The last column in this table shows the calculated spin moment for bcc Fe from PBE, PBE+U (which will be discussed in detail in the following section), HSE06, and GW. Our HSE06 result for bcc Fe agrees with previous work 46 and demonstrates that, although the screened hybrid functional method improves on the Hartree-Fock treatment of metallic systems, it can overestimate the strength of the exchange and yield un-physical high spin states. However, we also note that the calculated bcc Fe spin moment is not necessarily directly proportional to the calculated moments in α ′′ -Fe 16 N 2 , so it is possible that the bcc Fe moment does not completely determine the accuracy of a method in this case.…”

Iron in Hydroxyapatite: Interstitial or Substitution Sites?

“…The resulting ground state spin density corresponded to a magnetic moment of 2.80 µ B per cell. The deviation from the experimental value of 2.22 µB results from a known over-localization of the exchange interactions in bulk Fe when using hybrid functionals [44]. An identical result was obtained using projected augmented-wave potentials.…”

Optical gaps and excitons in semiconducting transition metal carbides (MXenes)

“…The amount of exact exchange in the HSE06 hybrid functional is possibly too large for metallic systems, which results in the overestimation of the exchange splitting. 43,44 We assume that similar overestimation of the exchange splitting can also explain the enhanced HSE06 magnetic moments of magnetic semiconducting MXenes.…”

“…42) and in calculations for Fe atoms in bulk Fe (ref. 43). The amount of exact exchange in the HSE06 hybrid functional is possibly too large for metallic systems, which results in the overestimation of the exchange splitting.…”