Local Spin Density Approximation Calculations Research Articles

Study of half-metallicity in LSMO

Self-interaction corrected local spin density approximation calculations were performed for La (1− x) Sr x MnO 3 (LSMO) ( x=0.7). A half-metallic state was obtained for LSMO with manganese configuration Mn 3+, whilst Mn 4+ gave rise to a metallic state with a negligible spin polarization at the Fermi level.

Delocalization and charge disproportionation inLa(1−x)SrxMnO3

Self-interaction corrected local spin density approximation calculations were performed for La$_{(1-x)}$Sr$_x$MnO$_3$ (LSMO) ($0.0<x<0.5$). The influence and inter-relationship of Sr doping, magnetic structure, O displacements and phase segregation on the Mn charge state were studied. A half-metallic state was obtained for LSMO with manganese configuration Mn$^{3+}$, whilst Mn$^{4+}$ gave rise to a metallic state with a negligible spin polarisation at the Fermi level. Elongating the MnO$_6$ octahedron led to a static mixed valence Mn$^{3+}$/Mn$^{4+}$ configuration. In the mixed valence state the total energy was minimized by an ordered array of Mn$^{4+}$ and Mn$^{3+}$ MnO$_2$ planes which showed charge ordered stripes.

Final state effects in the X-ray absorption spectra of La0.7Sr0.3MnO3

We present a comparison of theoretical calculations of the electronic structure of La0.7Sr0.3MnO3 with measurements of the unoccupied local density of states for Mn obtained from X-ray absorption spectroscopy (XAS). We compare two different theoretical calculations of the Mn XAS spectra, one based on the local spin density approximation (LSDA) and the other one based on an atomic Hartree–Fock calculation for the Mn ions. In the atomic calculation the solid state effects are introduced through a cubic crystal field where the crystal field strength is obtained from the LSDA calculation. It is found that the atomic calculations agree better with experimental data.

Atomic clusters of magnetic oxides: Structure and phonons

This work represents a combined experimental and theoretical study of structural and magnetic properties of clusters made of cobalt, chromium, and manganese oxides. The clusters were prepared in a molecular cluster source by oxidation of laser-vaporized metal and studied in a time-of-flight spectrometer. Infrared laser-induced cluster dissociation experiments revealed the spectrum of cluster vibrational states. We also performed ab initio local spin density approximation calculations of the equilibrium geometry, electronic structure, and magnetic properties of these clusters.

Electronic and magnetic structure ofURhGe

A consistent picture of the magnetic properties and electronic structure of the superconducting itinerant ferromagnet URhGe is obtained with the local spin-density approximation (LSDA). The LSDA calculations reproduce both the magnitude of the observed moment, composed of strongly opposing spin and orbital parts, and the magnetocrystalline anisotropy. It is shown that the canted magnetic structure of URhGe can originate from the noncollinear arrangement of U-atom orbital magnetic moments, while the spin magnetic moments are ferromagnetically ordered.

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.

Electronic structure of the double-perovskiteBa2FeMoO6using photoemission spectroscopy

The electronic structure of ${\mathrm{Ba}}_{2}{\mathrm{FeMoO}}_{6}$ (BFMO) has been investigated by using photoemission spectroscopy (PES). By varying $h\ensuremath{\nu}$ across the Mo $4d$ Cooper minimum, it is found that the states close to the Fermi level ${E}_{F}$ are predominantly of the Mo ${t}_{2g}\ensuremath{\downarrow}$ and Fe ${t}_{2g}\ensuremath{\downarrow}$ character. The measured PES spectrum is compared to the calculated electronic structure obtained in the local spin-density approximation (LSDA) and $\mathrm{LSDA}+U$ methods. The $\mathrm{LSDA}+U$ calculation yields better agreement with experiment in the peak positions than does the LSDA calculation. The present study supports the double exchange mechanism for the half-metallic ferrimagnetism in BFMO.

Surface charge density waves and the Mott insulators for [formula omitted] adlayers on [formula omitted] semiconductor surfaces

We discuss our recent studies on the low-temperature instabilities of the 3 × 3 phase of tetravalent adatoms on (1 1 1) semiconductor surfaces. The cases of interest include the surface charge density wave (CDW) systems Pb/Ge(1 1 1) and Sn/Ge(1 1 1), as well as the Mott insulators Si/SiC(0 0 0 1) and K/Si(1 1 1):B. We have approached the problem in two ways: first, by employing a one-band model Hamiltonian of the Hubbard–Holstein type, in order to understand general features of the phase diagram as a function of the strength of electron–electron (e–e) and electron–phonon (e–ph) interactions; second, by performing realistic ab initio calculations within the local spin density approximation (LSDA) for the case of Sn/Si(1 1 1), and of a hypothetical 3 × 3 Si/Si(1 1 1) mimicking K/Si(1 1 1):B. The collinear LSDA calculation for both Sn/Ge(1 1 1) and Si/Si(1 1 1) predicts a spin density wave (SDW) state with a uniform magnetization m z =1/3 and a small secondary CDW. We discuss and stress the likely important role played by e–e interactions in explaining the phenomenology of all these systems, as opposed to the secondary role played by the e–ph coupling, which would at most drive the lattice, for Pb–Sn/Ge(1 1 1), after the electrons have caused the transition.

Porphyrin-Fe(III)-hydroperoxide and porphyrin-Fe(III)-peroxide anion as catalytic intermediates in cytochrome P450-catalyzed hydroxylation reactions: a molecular orbital study

The hydroxylation of fluorobenzene and aniline, catalyzed by the porphyrin-Fe(III)-peroxide anion with either a cysteinate- or a histidyl-type of axial ligand as well as the hydroxylation of fluorobenzene, catalyzed by porphyrin-Fe(III)-hydroperoxide with a cysteinate-type of axial ligand as catalytic intermediates, have been investigated by electronic structure calculations in local spin-density approximation. Non-repulsive potential curves are, in contrast with porphyrin-Fe(III)-hydroperoxide, obtained only in the case of porphyrin-Fe(III)-peroxide anion as catalytic intermediate. The mutual substrate–porphyrin orientation with a dihedral angle between the plane of the substrate and the porphyrin plane of 45° is more favorable compared with the parallel orientation between these two planes. This orientation differs for the case of fluorobenzene hydroxylation from the corresponding one calculated by us with the ferryl-oxo-π-cation radical complex as a catalytic intermediate. The calculated reaction profiles show also the effectiveness of the histidyl-type coordinated porphyrin-Fe(III)-peroxide involved in P450 type of hydroxylation reactions. The calculations demonstrate the predominant role of the O 1O 2 moiety of the porphyrin-Fe(III)-peroxide anion in the hydroxylation process of the substrates. The results indicate that the porphyrin-Fe(III)-peroxide anion is an effective catalytic species in hydroxylation reactions. In all the studied cases irrespective of the substrate and the nature of the axial ligand, the potential curves reach minimum at approximately 130–140 pm, expressing the length of an aromatic CO bond.

Electronic structure of self-assembled quantum dots: comparison between density functional theory and diffusion quantum Monte Carlo

We have calculated the exchange, correlation, and total electronic energy of a realistic InAs self-assembled quantum dot embedded in a GaAs matrix as a function of the number of electrons in the dot. The many-body interactions have been treated using the local spin density approximation (LSDA) to density functional theory (DFT) and diffusion quantum Monte Carlo (DMC), so that we may quantify the error introduced by LSDA. The comparison shows that the LSDA errors are about 1–2 meV per electron for the system considered. These errors are small enough to justify the use of LSDA calculations to test models of self-assembled dots against current experimental measurements.

The electronic structure of La0.66Ca0.33MnO3 and La1.2Sr1.8Mn2O7 studied by angle resolved photoemission

We report angle resolved photoemission studies of La0.66Ca0.33MnO3 and La1.2Sr1.8Mn2O7 using single crystal samples. The Mn 3p–3d resonance photoemission data of La0.66Ca0.33MnO3 show that the states at 2.5 eV binding energy have predominantly Mn 3d character, qualitatively consistent with the predictions of local spin density approximation calculations except for a 1 eV shift toward higher binding energy. Band dispersions are observed in the normal emission data. The spectra of La1.2Sr1.8Mn2O7 show well defined features and strong matrix element effects, indicating excellent surface quality.

Electronic and magnetic properties of Li 2CuO 2

We have performed an electronic band calculation for non-magnetic (NM) and antiferromagnetic (AF) states of Cu–O edge-sharing compound Li 2CuO 2 by using the FLAPW method with local spin-density approximation (LSDA) and LSDA+U approximation. In the NM-state a narrow antibonding band crosses the Fermi level and consists of strongly hybridized Cu 3 d yz and O 2 p y states. The Fermi surface of the NM state reveals a nesting effect which plays an important role in causing the observed antiferromagnetic ordering. In the AF state the narrow antibonding band in the NM state is split and a small bandgap appears at the Fermi level. LSDA+U calculation leads to a much wider bandgap than the LSDA calculation.

Electronic structure study of the magnetoresistance materialCaCu3Mn4O12by LSDA andLSDA+U

The electronic structure of the large low-field magnetoresistance material ${\mathrm{CaCu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ is calculated by using the local-spin-density approximation (LSDA) and on-site Coulomb interaction correction $(\mathrm{LSDA}+\mathrm{U})$ to the $3d$ electronic states of Cu and Mn ions. The results obtained suggest a strong ionic character of this material despite a presence of a partial Mn-O covalence effect. Three Cu ions per formula cell have their respective half-filled orbitals ${d}_{\mathrm{xy}},{d}_{\mathrm{yz}},$ and ${d}_{\mathrm{xz}}$ due to their different local crystal environments. Four Mn ions per formula cell have nearly the same oxygen coordinations. As a consequence, the spin-up ${t}_{2g}$-like orbitals ${(d}_{\mathrm{xy}}{,d}_{\mathrm{yz}},$ and ${d}_{\mathrm{xz}})$ are almost full-filled, while the spin-up ${e}_{g}$-like orbitals ${(d}_{{3z}^{2}\ensuremath{-}{r}^{2}}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}})$ are partially occupied due to a finite $\mathrm{pd}$ hybridization. And it is shown that the sublattices of Cu ions and Mn ones are both aligned in ferromagnetic order, while these two sublattices are coupled antiferromagnetically, thus giving a net spin moment of 9 ${\ensuremath{\mu}}_{B}$ per formula. The $\mathrm{LSDA}+\mathrm{U}$ calculation yields a semiconducting solution, which is improved upon a half-metallic state given by the LSDA calculation and consistent with an experimental measurement.

The electronic structure of CaCuO2 and SrCuO2

We have calculated and compared the electronic structures of both the 1D CuO-chain compound SrCuO2 and the 2D CuO2-plane material CaCuO2, on the basis of the local-spin-density approximation (LSDA) and the on-site Coulomb interaction correction (LSDA+U). The LSDA calculation gives a nonmagnetic and metallic solution as usual for CaCuO2, while it yields an antiferromagnetic (AFM) and insulating one for SrCuO2 due to the decreasing pd hybridization and the subsequent spin polarization with lowering dimensionality. Strongly in favour of orbital and spin polarizations of the Cu 3d states, the U interaction dominates in forming the charge transfer insulating character of both of the AFM cuprates. Some of the differences between the electronic structures can be qualitatively accounted for by the variance of dimensionality.

Molecular orbital study of porphyrin–substrate interactions in cytochrome P450 catalysed aromatic hydroxylation of substituted anilines

The reaction mechanism for the primary reaction step of the hydroxylation of 3-fluoro-6-methylaniline, attacked at different positions (oxygen attack across a C–C bond and direct attack at positions para and ortho with respect to the NH 2-group) catalysed by a high-valent ferryl-oxo porphyrin a 2 u -cation complex with H 3CS − as an axial ligand, has been investigated on the basis of electronic structure calculations in local spin-density approximation. Non-repulsive potential curves are obtained only in cases of direct attack at the para- and ortho-positions with respect to NH 2, but not for epoxide formation. Comparing the potential curves for the hydroxylation at the positions para and ortho to the NH 2-group, an attack at the para-position is more likely. The relative orientation of the substrate towards the porphyrin is essentially determined by the interaction between the substituents of the substrate and the porphyrin. Consequently, different geometrical orientations of the substrate are obtained for hydroxylation at the para- and ortho-positions. In both cases of direct attack the substrate plane is not parallel to the porphyrin plane. The decisive role of sulphur in the hydroxylation is demonstrated by the participation of the S(3p)-orbitals in all molecular orbitals involved in the reaction.

Electronic structure of black sodalite

The electronic structure of black sodalite, ${\mathrm{Na}}_{8}{(\mathrm{A}\mathrm{l}\mathrm{S}\mathrm{i}\mathrm{O}}_{4}{)}_{6},$ is determined in the local-spin-density approximation (LSDA). This structure has six Na atoms to compensate the six Al atoms, leaving two excess Na atoms. A band-gap electronic state is induced in the wide oxide gap by the excess sodium, and has ``particle in a box'' behavior. Magnetic orderings of these gap states are studied. Analytic models show that an antiferromagnetic ordering is lowest in energy in the LSDA. A self-consistent LSDA calculation shows the system to change from a metal to an antiferromagnetic insulator when spin orderings are allowed. Hopping and Hubbard-U parameters are estimated, and the many-body correlated Hubbard model is solved using a constrained path Monte Carlo technique, which again predicts the system to be antiferromagnetic with a ${T}_{c}$ of order 50 K.

Electronic structure, local moments, and transport inFe2VAl

Local spin density approximation calculations are used to elucidate electronic and magnetic properties of Heusler structure Fe_2VAl. The compound is found to be a low carrier density semimetal. The Fermi surface has small hole pockets derived from a triply degenerate Fe derived state at Gamma compensated by an V derived electron pocket at the X point. The ideal compound is found to be stable against ferromagnetism. Fe impurities on V sites, however, behave as local moments. Because of the separation of the hole and electron pockets the RKKY interaction between such local moments should be rapidly oscillating on the scale of its decay, leading to the likelihood of spin-glass behavior for moderate concentrations of Fe on V sites. These features are discussed in relation to experimental observations of an unusual insulating state in this compound.

Valence states of copper ions and electronic structure ofLiCu2O2

The electronic structure of LiCu${}_{2}$O${}_{2}$ was studied using x-ray emission (Cu ${L}_{\ensuremath{\alpha}},$ O ${K}_{\ensuremath{\alpha}})$ and photoelectron spectroscopy (valence band and core levels) as well as band-structure calculations in terms of local spin-density approximation (LSDA) and LSDA+$U$ approaches. According to the x-ray-emission and photoelectron spectra the valence states of the Cu atoms are found to be mixed, i.e., 2+ and 1+. The LSDA calculations are contradictory to the experimental data and cannot reproduce the band gap and magnetic properties of ${\mathrm{LiCu}}_{2}{\mathrm{O}}_{2}$. The LSDA+$U$ calculations describe the insulator and antiferromagnetic properties much better but the overestimation of the screened Coulomb parameter $U$ leads to a binding-energy shift of the Cu${}^{\mathrm{II}}$ $3d$ states and this distorts the proper modeling of the valence-band structure. The magnetic structure of LiCu${}_{2}$O${}_{2}$ is discussed, taking our LSDA+$U$ band-structure calculations into account.

Valence-band spectra and electronic structure ofCuFeO2

The delafossite-type ${\mathrm{CuFeO}}_{2}$ single crystal was studied by means of x-ray emission and x-ray photoelectron spectroscopy. The valence state of Cu ions was found to be $1+,$ whereas Fe ions were found to be trivalent in the high-spin $S=5/2$ state. The x-ray emission (Cu ${L}_{\ensuremath{\alpha}},$ Fe ${L}_{\ensuremath{\alpha}},$ and O ${K}_{\ensuremath{\alpha}})$ and photoelectron spectra were compared to the results of the local spin density approximation (LSDA) (full-potential linearized augmented plane wave method and linearized muffin-tin orbitals in atomic sphere approximation method) and $\mathrm{LSDA}+U$ calculations. It is found that the maximum of the Cu $3d$ state distribution is localized closer to the Fermi level than that of the Fe $3d$ states. The LSDA calculations contradict the experimental results and do not give a correct description of the Cu and Fe $3d$ positions relative to the Fermi level, and incorrectly predict metallic behaviors (semiconductor observed) and give qualitatively incorrect magnetic properties of ${\mathrm{CuFeO}}_{2}.$ The $\mathrm{LSDA}+U$ calculations give a much better agreement with the observed valence-band structure, the measured electrical, and the magnetic properties.

Effect of Mott-Hubbard correlations on the electronic structure and structural stability of uranium dioxide

Abstract The influence of Mott-Hubbard electron-electron correlations on the electronic structure and structural stability of uranium dioxide (UO2) has been analysed using the local spin-density approximation (LSDA) + U approach. We have found that the inclusion of a term describing the Hubbard on-site repulsion between 5f electrons results in a dramatic improvement in the description of the equilibrium electronic and magnetic structure of UO2 for which conventional LSDA calculations incorrectly predict a non-magnetic metallic ground state. We have found that the presence of electron-electron correlations in the 5f band modifies the character of chemical bonding in the material, leading to a Heitler-London type of hybridization between the 5f orbitals and giving rise to a larger value of the equilibrium lattice constant in better agreement with experimental observations.