Self-consistent Energy Band Calculations Research Articles

Interface coupling induced built-in electric fields accelerate electro-assisted uranium extraction over Co3O4@FeOx nanosheet arrays

Revealing the nature of enhanced electro-assisted uranium extraction activity by hetero-interface and M-O-H coordination bonds is an important and challenging task. Hence, Co3O4@FeOx nanosheet arrays with abundant M-O-H coordination bonds is fabricated as a binder-free and self-supporting electrocatalyst for electro-assisted uranium extraction from fluorine-containing uranium wastewater. As revealed by self-consistent energy band calculations and in-situ Kelvin Probe Force Microscopy (KPFM) analysis, the p-n heterojunction formed by Co3O4@FeOx provides a well-designed built-in electric field (BIEF), triggering the interfacial accumulation of uranium and accelerating the electro reduction kinetics of uranium. Consequently, Co3O4@FeOx shows remarkable U(VI) extraction ability (>95 %) in fluorine-containing uranium wastewater. By virtue of the XAFS spectra, free uranyl ions are captured by M-O-H on Co3O4@FeOx to form a sturdy 2 Oax-1 U-3 Oeq configuration, confirming the electrically driven separation of uranium and fluorine. Furthermore, DFT calculation indicates that the existent of M-O-H enhances the adsorption energy of uranium species, thus promoting uranium extraction efficiency.

In Situ Metal-Oxygen-Hydrogen Modified B-Tio2 @Co2 P-X S-Scheme Heterojunction Effectively Enhanced Charge Separation for Photo-assisted Uranium Reduction.

Photo-assisted uranium reduction from uranium mine wastewater is expected to overcome the competition between impurity ions and U(VI) in the traditional process. Here, B-TiO2 @Co2 P-X S-scheme heterojunction with metal-oxygen-hydrogen (M-O-H) is developed insitu modification for photo-assisted U(VI) (hexavalent uranium) reduction. Relying on the DFT calculation and Hard-Soft-Acid-Base (HSAB) theory, the introduction of metal-oxygen-hydrogen (M-O-H, hard base) metallic bonds in the B-TiO2 @Co2 P-X is found to enhance the hydrophilicity and the capture capability for uranyl ion (hard acid). Accordingly, B-TiO2 @Co2 P-500 hybrid nanosheets exhibit excellent U(VI) reduction ability (>98%) in the presence of competing ions. By self-consistent energy band calculations and in-situ KPFM spectral analysis, the formation of the internal electric field between B-TiO2 and Co2 P at the heterojunction is proven, offering a strong driving force and atomic transportation highway for accelerating the S-scheme charge carriers directed migration and promoting the photocatalytic reduction of uranium. This work provides a valuable route to explore the functionally modified photocatalyst with high-efficiency photoelectron separation for U(VI) reduction.

Magnetovolume Effects in Strongly and Intermediately Correlated Electron Systems

Analyses of magnetovolume effects such as the forced volume magnetostriction and the thermal expansion anomaly can give estimation of local amplitude of spin fluctuations. We have shown that bcc Fe has a rigid magnetic moment and that the magnetic moment of Invar type alloys is rather soft. It is pointed out that the total energy difference between the magnetized state and the nonmagnetic state obtained by self-consistent energy band calculations using a local-spin-density approximation is much higher than the Curie temperature for rigid spin systems and comparable for soft spin systems. The effects of zero point spin fluctuations observed in the YMn2 system are discussed.

Comparison of various exchange potentials in self-consistent OPW energy band calculations for cubic ZnS and ZnSe

Self-consistent energy band calculations using the OPW method have been performed on cubic ZnS and ZnSe using Slater's, Kohn-Sham's and Liberman's exchange potentials. Term values are given for the four symmetry points T, ≥X, L, and W. The variation of the energy bands with the exchange coefficient is shown to be linear. The imaginary part of the dielectric constant (ϵE2) is calculated by means of a pseudopotential interpolation technique for the three exchange potentials. It is found that both the band gap and the position of the peaks of the ϵE2 curves agree very closely with experiment for the self-consistent results derived from Slater's exchange, while the disagreement is substantial for the self-consistent results derived from Kohn-Sham's and Liberman's exchange potential.

Isoelectronically substituted heavy-fermion compoundsCeCu6−xAux, studied by local probe and electronic band structure calculation

For $\mathrm{Ce}{\mathrm{Cu}}_{6\ensuremath{-}x}{\mathrm{Au}}_{x}$ $(x=0,0.1,1)$, we measured the temperature dependence of $^{63,65}\mathrm{Cu}$ nuclear magnetic resonance spectra of oriented single-crystal powder at $7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ in the $5--100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ range. ${\mathrm{Ce}}^{3+}$ crystal field and molecular field parameters are derived from single-crystal magnetic susceptibility data. Calculated electric field gradients are used to correctly assign nuclear quadrupole resonance frequencies to lattice sites $(n)$. Bare Knight shifts and transferred hyperfine interaction coupling constants $\ensuremath{\alpha}(n)$ as well as electric field gradient information are extracted for the various Cu sites $(n)$. Ab initio self-consistent energy-band calculations explain the electric field gradients and the alternation of the sign of $\ensuremath{\alpha}(n)$. The anisotropy of the hyperfine coupling parameter $\ensuremath{\alpha}$ is proved for the $a\text{\ensuremath{-}}c$ plane for the Cu(5) site.

The change in magnetic properties of Fe3Al compound due to substitution of Fe by Co

The magnetic moment using self-consistent spin-polarized energy band calculations of Fe 3 Al and Fe 2 CoAl Heusler phases are presented. These results are compared with the experimental values obtained from the magnetization curves of these materials.

Orbital magnetism in UFe2

Abstract The magnetization density of UFe 2 has been evaluated from self-consistent energy band calculations using screened exchange interactions. The calculated total magnetic moment is 1.4 μ B /f.u. and almost entirely due to an Fe moment of 0.72 μ B . The small uranium moment consists of spin and orbital moments of −0.19 and 0.17 μ B , respectively. The calculated magnetic amplitude is in excellent agreement with the results of neutron diffraction experiments. The calculated orbital contribution to the Fe moment of 0.1 μ B is one order of magnitude larger than measured.

The change in magnetic properties of Fe3Al compound due to substitution of Fe by Co

The magnetic moment using self-consistent spin-polarized energy band calculations of Fe3Al and Fe2CoAl Heusler phases are presented. These results are compared with the experimental values obtained from the magnetization curves of these materials.

GMR in Ni/Cu multilayers: an electronic structure study

Ab initio self-consistent semi-relativistic spin-polarized TB-LMTO energy band calculations have been carried out on Ni/Cu(100) multilayers, to study the in-plane as well as perpendicular to plane giant magnetoresistance (GMR) effects. The magnetic interaction energies, evaluated as a function of layer thickness, indicate that the antiferromagnetic ordering is a possible ground state for manifestation of GMR. Using the density of states at Fermi level and the Fermi velocity, GMR has been estimated as a function of the Cu spacer thickness.

An ab-initio Study of Optical Properties of Perovskites : LaMO3 and YMO3 (M = Ti-Cu)

A self-consistent first principles energy band calculation is performed. The energies and eigen functions thus obtained are used to calculate interband transition elements in dipole approximation. The imaginary part of the dielectric constant as well as the optical conductivities of perovskites LaMO 3 and YMO 3 (M=Ti-Cu) are calculated. The origin of the structures can be explained on the basis of their respective energy bands. When compared with available experimental data one finds a good agreement with theoretical results.

Calculated optical properties of thorium, protactinium, and uranium metals.

We report self-consistent energy band calculations using the linear muffin-tin orbital method and the local-spin-density approximation to exchange and correlation in density-functional theory for the light actinide metals Th, Pa, and U. The optical properties have been calculated and compared with measurements, where possible. The dependence of the optical response functions upon crystal structure was found to be surprisingly large and the dependence upon spin-orbit coupling, less so. Where it was possible to make comparison, agreement with experiment was obtained for the maxima of the optical spectra, the exception being a feature in the optical conductivity at 10 eV measured in both Th and U but not obtained in the calculations. \textcopyright{} 1996 The American Physical Society.

Calculated magneto-optical Kerr effect in Fe, Co, and Ni.

We report ab initio calculations of magneto-optical Kerr effect in Fe, Co, and Ni. Both real and imaginary parts of the interband optical response functions are calculated from self-consistent energy-band calculations in the presence of both a magnetic mo

Ground-state properties of ternary uranium compounds: I. Hybridization effects

We report self-consistent LMTO energy band calculations for the compounds U(T)Al with the ZrNiAl structure where T is a group 6-8 transition metal. The role of hybridization between transition metal d states and uranium f states is examined by analysis of the structure and modelling of the results of the self-consistent energy-band-structure calculations. It is found that these compounds belong to a class of strongly hybridizing materials where the bonding between the uranium f states and transition metal d states dominates.

Calculated ground state, optical and magneto-optical properties of uranium sulphide

We report the results of self-consistent energy band calculations of the charge and spin densities of uranium sulphide. The electronic structure was obtained using the linear muffin tin orbital method, with the local spin density approximation to exchange and correlation. Relativistic effects are examined in detail and the calculation of the orbital and spin contributions to the magnetic moment described. Calculated reflectivity and the magneto-optical Kerr rotation are compared with measurements.

Evidence for a magnetic moment at the Lu site of LuFe2

High pressure 175Lu NMR measurements of LuFe2 at 4.2 K suggest that Lu, like Y and Zr, carries a negative magnetic moment, in agreement with self-consistent energy band calculations. The observed spectrum is more complicated than would be expected for a Laves phase compound.

Self-consistent calculations of carrier distribution and energy bands in InGaAs/InP p-i-n diodes

One dimensional semiconductor device equations are solved for the double-heterojunction p-i-n diode using a state variable model. Using this model, Poisson equation and the current density equation are solved simultaneously in a single integration step. The boundary conditions at both the heterojunctions are satisfied for a given device geometry with abrupt junctions. The degeneracy of the semiconductor is considered in the simulations and the depletion width is obtained without the abrupt space-charge approximation. The numerical integration step is varied to ensure charge neutrality across the junctions. The integration is combined with Extended Kalman Filter to ensure consistency with the boundary conditions and among the variables. The electric field, the energy bands, and the carrier distributions obtained are self-consistent. The results obtained for two types of device structures, one grown with an undoped InP buffer layer and one without the buffer layer are discussed.

Electronic structure of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) and Nb by the pseudofunction energy-band technique.

The pseudofunction energy-band method is a full potential, ab initio technique with no adjustable parameters. The basis function is related to the pseudofunction used to create ab initio pseudopotentials. Orthogonalization of the pseudofunction to the core states is accomplished as in the augmented plane-wave method (APW) or linear augmented plane-wave method. The applicability of the pseudofunction method to both localized bonding as in molecules or to delocalized bonding as in metals is demonstrated with application to Nb and tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). The electronic and structural properties calculated for Nb agree well with that of the APW and Korringa-Kohn-Rostoker (KKR) methods. The energy bands obtained from an ab initio self-consistent energy-band calculation for TTF-TCNQ are successful in providing new insight into the properties of TTF-TCNQ. The computed optical properties, Fermi surface wave vector, and charge transfer agree quantitatively with experiment for TTF-TCNQ.

Magnetic and magneto-optical properties of uranium sulphide

The optical and magneto-optical properties of uranium NaCl-type compounds have been thoroughly investigated experimentally and a model of the electronic structure was proposed. From self-consistent LMTO energy band calculations, we obtain prominent peaks in the optical conductivity at 0.02, 1.2 and 2.0 eV in agreement with the observations. When spin-orbit coupling is included in the calculations we obtain both giant orbital contributions to the moment and magneto-optical Kerr effect.

Theory of the magnetism of ternary uranium compounds

Measurements suggest that the 5f electrons in the compounds UTAl (T = Fe, Co, Ni, Ru, Rh, Ir, Pt), which crystallize in the hexagonal ZrNiAl structure, are itinerant. From self-consistent LMTO energy band calculations for the compounds we explain the transition to magnetism across the series but show that the magnetism must contain an orbital contribution. Inclusion of spin-orbit interaction leads to large induced orbital moments in the magnetic compounds.

Symmetry of the unoccupied states in Cs graphite intercalation compounds by X-ray absorption

The X-ray photoabsorption spectra of the first three stages of cesium graphite intercalation compounds have been measured at the L absorption edges of Cs, using a linearly polarized synchrotron beam. The results are interpreted based on the self-consistent field energy band calculation for CsC 8. The L I spectra show strong dependence on the polarization angle of the incident radiation. The structures are well correlated with the p x , p y , and p z final states located on Cs sites. In L II and L III spectra the familiar white lines, characteristic of metals, are observed. These are attributed to transitions to unoccupied states with atomic d character at Cs sites. The results also indicate that the charge transfer between Cs and C layers in CsC 8 is nearly unity.