HSE hybrid functional within the FLAPW method and its application to GdN

Abstract

We present an implementation of the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional within the fullpotential linearized augmented-plane-wave (FLAPW) method. Pivotal to the HSE functional is the screened electron-electron interaction, which we separate into the bare Coulomb interaction and the remainder. Both terms give rise to exchange potentials, which sum up to the screened nonlocal exchange potential of HSE. We evaluate the former with the help of an auxiliary basis, defined in such a way that the bare Coulomb matrix becomes sparse. The latter, which is a slowly varying function in real space, is computed efficiently in reciprocal space. This approach is general and can be applied to a whole class of screened hybrid functionals. We obtain excellent agreement of band gaps and lattice constants for prototypical semiconductors and insulators with electronic-structure calculations using plane-wave or Gaussian basis sets. We apply the HSE hybrid functional to examine the ground-state properties of rocksalt GdN, which have been controversially discussed in literature. Our results indicate that there is a half-metal to insulator transition occurring between the theoretically optimized lattice constant at 0 K and the experimental lattice constant at room temperature. Overall, we attain good agreement with experimental data for band transitions, magnetic moments, and the Curie temperature.

Exchange parameters and adiabatic magnon energies from spin-spiral calculations

“…Furthermore that a single value of Hubbard U exists that results in a satisfactory description of all available experimental properties is not always the case [16]. This points to the limitation of the LDA+U method itself.…”

“…DFT functionals such as the local density approximation (LDA) and the generalized gradient approximation (GGA) are not able to describe strong electron correlation. Beyond DFT methods such as the LDA+U [4][5][6][7][8][9], Self interaction correction (SIC) [10][11][12], dynamical mean field theory (DMFT) [13], hybrid funtionals [14][15][16] and GWapproximation [17,18] have been employed with greater success improving the correspondence between calculated and experimental properties such as lattice parameters, band gaps and excitation energies for magnons and phonons. In this study we employ the LDA+U method for this class of materials.…”

Structural, electronic, and magnetic properties of the europium chalcogenides: A hybrid-functional DFT study

“…We employ the all-electron full-potential linearizedaugmented-plane-wave (FLAPW) method as realized in the FLEUR code, 39 in which the hybrid functionals PBE0 and HSE have been recently implemented. 40,41 The Brillouin zone is sampled by an 8 × 8 × 8 k-point mesh for all materials and we incorporate one local orbital for the first unoccupied s, p, d, and f states per atom. 42 All other important numerical parameters for the calculation depend on the particular compound and are listed in Table I.…”

“…(2) and (3) up to 1 meV, which corresponds to a possible error in the critical temperatures of 3 K. (ii) The critical temperature determined from the Monte Carlo simulation differs slightly from other theoretical approaches, e.g., the random-phase approximation, which may be associated to an error of roughly 10%. 41 (iii) The thermal expansion of the compounds between 0 K and the magnetic ordering temperature may account for an additional change in the coupling strength. Evaluating the coupling strengths once at the liquid-helium and once at the room-temperature lattice constant, we find that this expansion of the lattice constant is associated to a decrease of the Curie temperature in EuO of roughly 10 K. (iv) For a better description of the strongly localized f electrons in Eu, a slightly larger fraction of Hartree-Fock could be more suitable, which would decrease the ordering temperature.…”

The effects of strong correlations on the band structure of Ag8SnSe6 argyrodite

“…and 1 (b), is obviously caused by a partial removal of the Coulomb's self-interaction from the exchangecorrelation potential in equation (2.4), setting a non-zero coefficient α. Self-interaction leads to systematic errors in the band gap values of semiconductors and dielectrics [19,20]. Figure 2 shows that Ag 4d electrons are localized in a narrow energy range and are characterized by high values of density of states.…”