Results Of Local Spin Density Approximation Research Articles

Structural, electronic and magnetic properties of FCC Ba2CoBO6 [B = Mo, W, Re, Os]: LSDA+U+SOC comparative investigation

First-principles calculations by the full potential linear muffin-tin orbital (FP-LMTO) method using local spin density approximation (LSDA), taking into account of both spin orbital coupling (SOC) and strong correlation (U) within the framework of spin-polarized density functional theory (DFT), were carried out for the structural, electronic and magnetic properties of a series of double perovskites Ba2CoBO6 (B=Mo, W, Re, Os). Structural optimizations of lattice constants show that all Ba2CoBO6 compounds crystallize in face-centered cubic (FCC) system with space group of (Fm3¯m), in good agreement with the experimental values. The relative stability of ferromagnetic (FM) and antiferromagnetic (AFM) orders is discussed. It is shown that it consistent with experimental results and AFM order is obtained when using LSDA and LSDA+U methods. The magnetic results show that the double perovskites Ba2CoBO6 are AFM through the anti-coupling Co2+ (3d7)↑–O2− (2p)–B6+ (4d/5d)n↓, where n=0, 1 or 2. DFT results show that the Ba2CoBO6 are half-metallic (HM) with energy-gaps in spin-up bands, but if B=Mo, it shows metallic nature in LSDA results, and it established that the U responsible for the AFM-HM in Ba2CoBO6.

Many-body effects in x-ray absorption and magnetic circular dichroism spectra within the LSDA+DMFT framework

The theoretical description of photoemission spectra of transition metals was greatly improved recently by accounting for the correlations between the d electrons within the local spin density approximation (LSDA) plus dynamical mean field theory (DMFT). We assess the improvement of the LSDA+DMFT over the plain LSDA in x-ray absorption spectroscopy, which --- unlike the photoemission spectroscopy --- is probing unocccupied electronic states. By investigating the L2,3-edge x-ray absorption near-edge structure (XANES) and x-ray magnetic circular dichroism (XMCD) of Fe, Co, and Ni, we find that the LSDA+DMFT improves the LSDA results, in particular concerning the asymmetry of the L3 white line. Differences with respect to the experiment, nevertheless, remain --- particularly concerning the ratio of the intensities of the L3 and L2 peaks. The changes in the XMCD peak intensities invoked by the use of the LSDA+DMFT are a consequence of the improved description of the orbital polarization and are consistent with the XMCD sum rules. Accounting for the core hole within the final state approximation does not generally improve the results. This indicates that to get more accurate L2,3-edge XANES and XMCD spectra, one has to treat the core hole beyond the final state approximation.

Optical and magneto-optical properties of gadolinium

We report calculations of the optical and magneto-optical properties of elemental rare earth gadolinium using the full potential linear augmented plane wave method and including spin-orbit coupling. Calculations are performed within the local spin density approximation (LSDA) and Coulomb corrected local spin density approximation (LSDA+U). While LSDA+U gives better agreement for density of states and magnetic moments, a comparison with the experimental data shows that both LSDA and LSDA+U are at par in representing the diagonal components of the optical conductivity. For the much smaller off-diagonal components, interestingly, the LSDA results have an edge over the LSDA+U results.

Energy functional dependence of exchange coupling and magnetic properties ofFe∕Nbmultilayers

We present an ab initio calculation of the exchange coupling for $\mathrm{Fe}∕\mathrm{Nb}$ multilayers using the self-consistent full-potential linearized augmented plane-wave method. The exchange correlation potential has been treated in the local spin density approximation (LSDA) as well as generalized gradient approximation (GGA). We find that for the LSDA as well as the GGA the exchange coupling oscillates with a period of $6.0\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ of Nb spacer thickness which is close to the experimental value in the pre-asymptotic region. This is also close to the earlier calculated period (i.e., $4.5\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$) by augmented spherical wave method. The LSDA shows antiferromagnetic coupling for 2 and $5\phantom{\rule{0.3em}{0ex}}\mathrm{Nb}$ monolayers but the GGA shows the ferromagnetic coupling for all Nb spacer layers. The period of oscillation is found to be in good agreement with the period calculated using the Ruderman-Kittel-Kasuya-Yosida and quantum well models. The magnetic moment of Fe is found to be higher in the GGA than the LSDA. Fe magnetic moment also shows strong oscillations as a function of the spacer layer thickness, in agreement with the experimental results. We find that the GGA results show better agreement with the experiment than the LSDA results.

Therole of Coulomb correlation in magnetic and transport properties ofdoped manganites: La0.5Sr0.5MnO3 andLaSr2Mn2O7

Results of local spin-density approximation (LSDA) and LSDA + Ucalculations of the electronic structure and magneticconfigurations of the 50% hole-doped pseudocubic perovskiteLa0.5Sr0.5MnO3 and double-layeredLaSr2Mn2O7 are presented. We demonstrate that theon-site Coulomb correlation (U) of Mn d electrons has a verydifferent influence on the (i) band structures, (ii) magnetic ground states, (iii) interlayer exchangeinteractions, and (iv) anisotropy of the electrical transport in these two manganites. A p-dhybridization analysis is employed to look for possible explanationsfor the LSDA failing to predict the observed magnetic and transportproperties of the double-layered compound - in contrast to the casefor the doped perovskite manganite.

Electronic structure calculations for layered LaSrMnO4 and Ca2RuO4

The electronic structures and magnetic properties of layered perovskite LaSrMnO4 and Ca2RuO4 have been determined using the full-potential linearized augmented-plane-wave method within the local spin-density approximation (LSDA) and the LDA + U approach (LDA standing for local density approximation). The results of LSDA and LDA + U total-energy calculations show that the antiferromagnetic state of these materials is stable compared with the ferromagnetic and paramagnetic states. The LDA + U calculation results show that Jahn–Teller distortion of Mn–O and Ru–O octahedra produces an energy gap, and 3z2 − r2 and xy orbital ordering for LaSrMnO4 and Ca2RuO4, respectively. However, the LSDA calculation is not sufficient for describing the orbital ordering and fails to produce the band gap. The Jahn–Teller distortion stabilizes a two-dimensional planar antiferromagnetic state.

First-principles calculations for vacancy formation energies in Cu and Al; non-local effect beyond the LSDA and lattice distortion

We show ab initio calculations for vacancy formation energies in Cu and Al. The calculations are based on density-functional theory and the full-potential Korringa–Kohn–Rostoker Green's function method for impurities. The non-local effect beyond the local-spin-density approximation (LSDA) for density-functional theory is taken into account within the generalized-gradient approximation (GGA) of Perdew and Wang. The lattice relaxation around a vacancy is also investigated using calculated Hellmann–Feynman forces exerted on atoms in the vicinity of a vacancy. We show that the GGA calculations reproduce very well the experimental values of vacancy formation energies and bulk properties of Cu and Al, as they correct the deficiency of LSDA results (underestimation of equilibrium lattice parameters, overestimation of bulk moduli, and vacancy formation energies). It is also shown that the GGA calculations reduce the LSDA results for the lattice relaxation energy for a vacancy in Cu.

Ab initio pseudopotential study of Fe, Co, and Ni employing the spin-polarized LAPW approach.

The ground-state properties of Fe, Co, and Ni are studied with the linear-augmented-plane-wave (LAPW) method and norm-conserving pseudopotentials. The calculated lattice constant, bulk modulus, and magnetic moment with both the local-spin-density approximation (LSDA) and the generalized gradient approximation (GGA) are in good agreement with those of all-electron calculations, respectively. The GGA results show a substantial improvement over the LSDA results, i.e., better agreement with experiment. The accurate treatment of the nonlinear core-valence exchange and correlation interaction is found to be essential for the determination of the magnetic properties of 3d transition metals. The present study demonstrates the successful application of the LAPW pseudopotential approach to the calculation of ground-state properties of magnetic 3d transition metals.

Electronic structure ofPrBa2Cu3O7: A local-spin-density approximation with on-site Coulomb interaction

Electronic structure calculations based on the local-spin-density approximation (LSDA) fail to reproduce the antiferromagnetic ground state of ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ (PBCO). We have performed linear muffin-tin orbital--atomic sphere approximation calculations, based on the local-spin-density approximation with on-site Coulomb correlation applied to Cu(1) and Cu(2) 3d states. We have found that inclusion of the on-site Coulomb interaction modifies qualitatively the electronic structure of PBCO with respect to the LSDA results, and gives Cu spin moments in good agreement with the experimental values. The Cu(2) upper Hubbard band lies about 1 eV above the Fermi energy, indicating a ${\mathrm{Cu}}^{\mathrm{II}}$ oxidation state. On the other hand, the Cu(1) upper Hubbard band is located across the Fermi level, which implies an intermediate oxidation state for the Cu(1) ion, between ${\mathrm{Cu}}^{\mathrm{I}}$ and ${\mathrm{Cu}}^{\mathrm{II}}$. The metallic character of the CuO chains is preserved, in agreement with optical reflectivity [K. Takenaka et al., Phys. Rev. B 46, 5833 (1992)] and positron annihilation experiments [L. Hoffmann et al., Phys. Rev. Lett. 71, 4047 (1993)]. These results support the view of an extrinsic origin of the insulating character of ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$.

Self-interaction correction for an impurity resonance state in metals.

The self-interaction correction (SIC) to the local-spin-density approximation (LSDA) is studied for a single impurity problem in metals. Although the impurity resonance state is a scattering state, we find that a localized orbital, for which the SIC should be considered, is obtained as in the case where the impurity state forms a real bound state. Model calculation shows that the exchange splitting of the virtual bound state is remarkably enhanced by SIC suggesting that the SIC-LSDA calculation achieves improvement of the LSDA results. A scheme to determine the occupation number of orbitals self-consistently in order to deal with the fractional occupation for metallic systems is also discussed.

Orbital functional for exchange and correlation: self-interaction correction to the local density approximation

The local spin-density approximation (LSDA) for electronic exchange and correlation is corrected by subtraction of the residual self-interaction of each orbital, yielding an orbital functional theory as a direct generalization of density functional theory. In contrast to results of LSDA or Xα, accurate results are obtained for the total and correlation energies of light atoms, the long-range behavior of the density, and the stability of negative ions.