Fock exchange energy is used instead of the local density approximation ͑LDA͒ or generalized gradient approximation ͑GGA͒ functional, as suggested recently ͓P. Novák et al., Phys. Status Solidi B 243, 563 ͑2006͔͒. If this is done only inside the atomic spheres, using an augmented plane wave scheme, a significant simplification and reduction of computational cost is achieved with respect to the usual but costly implementation of the Hartree-Fock formalism in solids. Starting from this, we construct exchange-correlation energy functionals of the hybrid form like B3PW91, PBE0, etc. These functionals are tested on the transition-metal monoxides MnO, FeO, CoO, and NiO, and the results are compared with the LDA, GGA, LDA+ U, and experimental ones. The results show that the proposed method, which does not contain any system-dependent input parameter, gives results comparable or superior to the ones obtained with LDA+ U which is designed to improve significantly over the LDA and GGA results for systems containing strongly correlated electrons. The computational efficiency, similar to the LDA+ U one, and accuracy of the proposed method show that it represents a very good alternative to LDA+ U.
A material is said to exhibit dichroism if its photon absorption spectrum depends on the polarization of the incident radiation. In the case of X-ray magnetic circular dichroism (XMCD), the absorption cross-section of a ferromagnet or a paramagnet in a magnetic field changes when the helicity of a circularly polarized photon is reversed relative to the magnetization direction. Although similarities between X-ray absorption and electron energy-loss spectroscopy in a transmission electron microscope (TEM) have long been recognized, it has been assumed that extending such equivalence to circular dichroism would require the electron beam in the TEM to be spin-polarized. Recently, it was argued on theoretical grounds that this assumption is probably wrong. Here we report the direct experimental detection of magnetic circular dichroism in a TEM. We compare our measurements of electron energy-loss magnetic chiral dichroism (EMCD) with XMCD spectra obtained from the same specimen that, together with theoretical calculations, show that chiral atomic transitions in a specimen are accessible with inelastic electron scattering under particular scattering conditions. This finding could have important consequences for the study of magnetism on the nanometre and subnanometre scales, as EMCD offers the potential for such spatial resolution down to the nanometre scale while providing depth information--in contrast to X-ray methods, which are mainly surface-sensitive.
Ab initio electronic structure calculations of actinide compounds have a weak point when the spin-orbit coupling is treated using a scalar-relativistic basis and the second variational method due to the poor description of the 6p states. We extend the basis set of the second variational step by including relativistic p 1/2 local orbitals for the description of the 6p states. Our results show that the additional p 1/2 local orbitals significantly improve the description of actinides.
-Metal-insulator transitions and other electronic transitions. PACS. 71.15.Mb -Density functional theory, local density approximation, gradient and other corrections.Abstract. -The electronic structure of the monoclinic structure of Fe3O4 is studied using both the local density approximation (LDA) and the LDA+U . The LDA gives only a small charge disproportionation, thus excluding that the structural distortion should be sufficient to give a charge order. The LDA+U results in a charge disproportion along the c-axis in good agreement with the experiment. We also show how the effective U can be calculated within the augmented plane wave methods.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.