Local Spin Density Approximation Calculations Research Articles

Simulation of the Adsorption and Diffusion of Lithium Atoms on Defective Graphene for a Li-Ion Battery

Based on the density functional theory (DFT) with allowance for spin polarization or the local spin density approximation (LSDA), we calculate the adsorption and diffusion properties of a lithium atom on a graphene ( ) monolayer with monovacancy ( ) as the anode material for an -ion battery. The DFT LSDA calculations are performed in relaxed 5 × 5 and 6 × 6 supercells and based on graphene with the monovacancy + lithium adatom complex . Based on the calculated values of the adsorption energy of the lithium atom , the energetically stable location of the lithium adatom is determined on a monolayer of supercells in and . The calculation results show that the adatom energetically prefers to be adsorbed in the pit position (H-site) rather than adsorbed from above (T-site) of the carbon atom in the monolayer. The DFT LSDA calculated electronic band structure and local total and partial magnetic moment of supercell atoms are consistent with the calculations performed by the generalized gradient approximation (GGA)-PBE functional for the H-, B-, and T-sites of graphene. Taking into account the experimentally obtained diffusion coefficients of lithium in two-layer graphene in the struc-tural packing of an AB package and the temperature (263–333 K) dependence of Li diffusion in two-layer graphene, which is described by the Arrhenius law, the diffusion activation energy of is calculated at con-centrations of = 0.06–0.51 in LixC12 graphene in the AB packaging.

Exchange interactions in hexagonal YMnO3 and LuMnO3 multiferroic compounds

In this work, spin density functional theory calculations are employed to obtain the exchange interactions in hexagonal YMnO3 and LuMnO3 multiferroic compounds, which have been a matter of debate in the literature. The exchange and correlation electronic effects are approximated using the local spin density approximation (LSDA) with the inclusion of the effective Hubbard U correction (Ueff). The intraplane superexchange interaction (Jnn) decreases with increasing Ueff. Moreover, the Jnn value with the best agreement with experiment is found for Ueff values between 2.55 and 4.0 ​eV. Without the addition of Ueff corrections, i.e., with standard LSDA calculations, the magnitude of Jnn is overestimated. The Bader topological analysis of the electron density at the bond critical point shows that the closed-shell interaction of the Mn–O3 and Mn–O4 bonds in both materials increases with increasing Ueff, which justifies the decrease of Jnn with increasing Ueff.. Additionally, both interplane and intraplane super-superexchange interactions are computed and compared with previous studies.

Effect of Temperature and Pressure on Structural and Magnetic Properties of Strontium-Filled Skutterudites SrT4Sb12: LDA and LSDA Calculations

The structural, elastic, thermodynamic, magnetic, and electronic properties of strontium-filled skutterudite component SrFe4Sb12 using the full potential-linear muffin-tin orbital (FP-LMTO) calculation were studied. The local density approximation (LDA) and local spin density approximation (LSDA) for predicting the physical properties were used. The internal parameters used to calculate the ground state properties such as lattice constant, bulk modulus, and its derivative pressure were optimized. Then, we have deduced the elastic constants, shear modulus G, Young modulus E, Poisson’s ratio ν, anisotropic parameter A, ratio B/G, and the Debye temperature (𝜃 D). The quasi-harmonic Debye model as implemented in the Gibbs program is applied to determine the thermal properties such as the Debye temperature (𝜃 D), heat capacity C v and C p , thermal expansion coefficient α Helmholtz free energy (A), Gibbs free energy (G), entropy (S) and internal energy (U) at different pressures and temperatures.

Electronic, structural and magnetic properties of TbO under pressure: FP-LAPW study

ABSTRACTUsing the framework of the density functional theory, we calculated electronic, magnetic and structural properties of terbium oxide (TbO) in rocksalt (RS), cesium chloride (CsCl) and zincblende (ZB). Full potential linearized augmented plane wave (FP-LAPW) method within the local spin density approximation (LSDA) and generalized gradient (PBE-GGA) approximations are used. Magnetic and non-magnetic calculations are performed and a modified version of Becke and Johnson (mBJ) exchange potential has been used to calculate the band gaps. We found that, although TbO is stable in a ferromagnetic state, it is stable in RS phase at ambient condition. Both LSDA and PBE-GGA calculations revealed that the three structures are metallic. However, using the mBJ calculation, it is clear that RS and CsCl phases of TbO compound are metallic, while ZB phase is found to be an insulator in the spin-up case and a semiconductor in the spin-down case at ambient pressure.

Synthesis, crystal structure and physical properties of the thulium filled skutterudite TmFe4P12 under the effect of the pressure: LDA and LSDA calculation

Ab-initio study of structural, electronic, elastic and thermodynamic, properties of the filled skutterudite TmFe4P12 has been reported using the FP-LMTO method with the local density approximation (LDA) and the local spin-density approximation (LSDA). The computed equilibrium lattice constants are an excellent agreement with the experimental data. The electronic band structure and densities of states profiles show that the studied compound is conductors. The elastic constants, the bulk modulus B, anisotropy factor A, shear modulus G, young's modulus E, Poisson's ratio ν and the ratio B/G for TmFe4P12 compound with pressure in the ranges 0–50GPa are obtained. The sound velocities and Debye temperature are also predicted from elastic constants. Finally, the variations of the primitive cell volume, expansion coefficient α, bulk modulus B, heat capacity (Cp and Cv), Debye temperature θD, Helmholtz free energy A, Gibbs free energy G, entropy S, and internal energy U with pressure and temperature in the ranges of 0–50GPa and 0–3000K are obtained successfully.

Effects of rare-earth size on the electronic structure of La1−xLuxVO3

The electronic structure of La1−xLuxVO3(x = 0, 0.2, 0.6 and 1) single crystals has been investigated using soft x-ray absorption spectroscopy, soft x-ray emission spectroscopy, and resonant soft x-ray inelastic scattering to study the effects of rare-earth size. The x-ray absorption and emission spectra at the O K-edge present a progressive evolution with R-site cation, in agreement with local spin density approximation calculations. This evolution with R, together with the temperature dependence of the O K-edge spectra, is attributed to changes in the crystal structure of La1−xLuxVO3. The crystal-field dd* excitations probed by resonant inelastic x-ray scattering at the V L3-edge exhibit an increase in energy and enhanced intensity with the decrease of R-site ionic radius, which is mainly attributed to the increased tilting magnitude of the VO6 octahedra. Upon cooling to ∼95 K, the dd* excitations are prominently enhanced in relative intensity, in agreement with the formation of the Jahn–Teller distortion in the orbital ordering phase. Additionally, the dd* transitions of the mixed compounds are noticeably suppressed with respect to those of the pure compounds, possibly owing to the formation of C-type orbital ordering induced by large R-site size variances.

Site-specific electronic structures of ferrimagnetic Fe3O4 measured by resonant X-ray magnetic scattering

Resonant magnetic scattering of circularly polarized synchrotron X-rays has revealed the site-specific magnetic moments at two non-equivalent Fe ion sites in Fe3O4. The energy-dependent peaks for the 026 and 266 reflections were attributed ferrimagnetically to the e and t 2 energy levels of Fe 3d at the A site, and to the t 2g and e g levels at the B site, respectively, having a sequence of t 2g, e, e g and t 2 in order of energy. This sequence agrees with the local spin-density approximation calculations in the literature [Anisimov, Elfimov, Hamada & Terakura, (1996). Phys. Rev. 54, 4387–4390], in which the spin-down band at the Fermi energy corresponds to t 2g . Resonant magnetic Fourier synthesis reveals the electron densities of the ferrimagnetic moments.

How to represent crystal structures for machine learning: Towards fast prediction of electronic properties

High-throughput density functional calculations of solids are highly time-consuming. As an alternative, we propose a machine learning approach for the fast prediction of solid-state properties. To achieve this, local spin-density approximation calculations are used as a training set. We focus on predicting the value of the density of electronic states at the Fermi energy. We find that conventional representations of the input data, such as the Coulomb matrix, are not suitable for the training of learning machines in the case of periodic solids. We propose a novel crystal structure representation for which learning and competitive prediction accuracies become possible within an unrestricted class of $spd$ systems of arbitrary unit-cell size.

Antiferromagnetic ground state in NpCoGe

NpCoGe, the neptunium analog of the ferromagnetic superconductor UCoGe, has been investigated by dc magnetization, ac susceptibility, specific heat, electrical resistivity, Hall effect, Np M\"ossbauer spectroscopy, and local spin-density approximation (LSDA) calculations. NpCoGe exhibits an antiferromagnetic ground state with a N\'eel temperature ${T}_{N}\ensuremath{\approx}13$ K and an average ordered magnetic moment $\ensuremath{\langle}{\ensuremath{\mu}}_{\mathrm{Np}}\ensuremath{\rangle}=0.80\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$. The magnetic phase diagram has been determined and shows that the antiferromagnetic structure is destroyed by the application of a magnetic field (\ensuremath{\approx}3 T). The value of the isomer shift suggests a Np${}^{3+}$ charge state (configuration $5{f}^{4}$). A high Sommerfeld coefficient value for NpCoGe (170 mJ mol${}^{\ensuremath{-}1}$ K${}^{\ensuremath{-}2}$) is inferred from specific heat. LSDA calculations indicate strong magnetic anisotropy and easy magnetization along the $c$ axis. M\"ossbauer data and calculated exchange interactions support the possible occurrence of an elliptical spin-spiral structure in NpCoGe. The comparison with NpRhGe and uranium analogs suggests the leading role of 5f-d hybridization, the rather delocalized character of 5f electrons in NpCoGe, and the possible proximity of NpRuGe or NpFeGe to a magnetic quantum critical point.

Evaluation of half-metallic antiferromagnetism inA2CrFeO6(A=La, Sr)

The nearly well-ordered double perovskite La${}_{2}$CrFeO${}_{6}$ has been synthesized recently. Contrary to previous theoretical predictions, but in agreement with experimental observations, our first principle calculations indicate an insulating ferrimagnet La${}_{2}$CrFeO${}_{6}$ with antialigned $S=3/2$ Cr${}^{3+}$ and $S=5/2$ Fe${}^{3+}$ ions, using the local spin density approximation (LSDA), a correlated band theory LDA+U, and the Tran-Blaha modified Becke-Johnson method. Additionally, we investigated the double perovskite Sr${}_{2}$CrFeO${}_{6}$, which is as yet unsynthesized. In LSDA calculations, this system shows formally tetravalent Cr and Fe ions both having antialigned $S=1$ moments, but is a simple metal. Once applying on-site Coulomb repulsion $U$ on both Cr and Fe ions, this system becomes half metallic and the moment of Fe is substantially reduced, resulting in zero net moment. These results are consistent with our fixed spin moment studies. Our results suggest a precisely compensated half-metallic Sr${}_{2}$CrFeO${}_{6}$.

Ab initiocomputational and experimental investigation of the electronic structure of actinide 218 materials

We report a comprehensive investigation of the electronic structure and magnetic properties of actinide 218 compounds, which crystallize in the tetragonal ${\text{Ho}}_{2}{\text{CoGa}}_{8}$ crystal structure. Specifically, we study experimentally the group of plutonium-based compounds ${\text{Pu}}_{2}M{\text{Ga}}_{8}$ (with $M=\text{Rh}$, Co, and Fe), which are structurally related to the unconventional superconductors ${\text{PuCoGa}}_{5}$ and ${\text{PuRhGa}}_{5}$ and are measured to be nonmagnetic and nonsuperconducting down to 2 K, yet displaying relatively high linear specific-heat coefficients of 61 to $133\text{ }\text{mJ}/\text{mol}\text{ }{\text{K}}^{2}$. We perform density-functional theory based calculations, in which we apply three different approaches to access the tendency of $5f$ electron localization, the local spin-density approximation (LSDA), $\text{LSDA}+U$, and the $5f$ open-core approach. For comparison to the above-mentioned compounds we also investigate computationally the plutonium compounds with $M=\text{Ir}$ and Pd, the uranium-based compounds ${\text{U}}_{2}M{\text{Ga}}_{8}$ (with $M=\text{Co}$, Fe, Rh, and Ru), as well as ${\text{Np}}_{2}{\text{CoGa}}_{8}$, and ${\text{Am}}_{2}{\text{CoGa}}_{8}$. On the basis of ab initio LSDA calculations we optimize the equilibrium lattice parameters and the internal fractional coordinates within the ${\text{Ho}}_{2}{\text{CoGa}}_{8}$ crystal structure. The obtained lattice parameters are in relatively good agreement with experimental values, when we assume delocalized $5f$ states for all compounds except ${\text{Am}}_{2}{\text{CoGa}}_{8}$. We discuss the computed electronic structures and the theoretical Fermi surfaces. For the Pu-218 compounds we find that LSDA calculations, in which the $5f$'s are treated as delocalized, predict a magnetically ordered ground state, whereas $\text{LSDA}+U$ calculations predict a nonmagnetic ground state in accordance with experiment. For the U-218 compounds the LSDA itinerant $5f$ approach predicts a nonmagnetic ground state, in accordance with available experimental data. For ${\text{Am}}_{2}{\text{CoGa}}_{8}$ our calculations are consistent with the scenario of localized $5f$ electrons. We find that, on account of the elongated tetragonal structure, most of the theoretical Fermi surfaces are quasi-two-dimensional.

Magneto-structural correlations in double-bridged [Cu2F6]2-

A direct approach for calculating magnetic coupling constants is presented. For the double-bridged copper dimer [Cu2F6]2- the results compare well with fully numerical calculations in local spin-density approximation.

Unusual quasiparticle renormalizations from angle resolved photoemission on USb2

Angle-resolved photoemission experiments have been performed on USb2, and very narrow quasiparticle peaks have been observed in a band, which local spin-density approximation (LSDA) predicts to osculate the Fermi energy. The observed band is found to be depressed by 17 meV below the Fermi energy. Furthermore, the inferred quasiparticle dispersion relation for this band exhibits a kink at an energy of about 23 meV below the Fermi energy. The kink is not found in LSDA calculations and, therefore, is attributable to a change in the quasiparticle mass renormalization by a factor of approximately 2. The existence of a kink in the quasiparticle dispersion relation of a band that does not cross the Fermi energy is unprecedented. The kink in the quasiparticle dispersion relation is attributed to the effect of the interband self-energy, involving transitions from the osculating band into a band that does cross the Fermi energy.

Electronic Properties, Band Structure, and Fermi Surface Instabilities ofNi1+/Ni2+NickelateLa3Ni2O6, Isoelectronic with Superconducting Cuprates

Electronic structure calculations were performed for the mixed-valent Ni(1+)/Ni(2+) nickelate La3Ni2O6, which exhibits electronic instabilities of the Fermi surface similar to that of the isostructural superconducting La2CaCu2O6 cuprate. La3Ni2O6 shows activated hopping, which fits to Mott's variable-range-hopping model with localized states near the Fermi level. However, a simple local spin density approximation calculation leads to a metallic ground state. The calculations including local density approximation+Hubbard U and hybrid functionals indicate a multiply degenerate magnetic ground state. For electron-doped La2ZrNi2O6, which is isoelectronic with La2CaCu2O6, an antiferromagnetic insulating ground state is found when correlations are included. The nickelates are thus ideal model systems for a deeper understanding of correlated transition metal compounds, magnetism, and superconductivity.

CaCrO3: An Anomalous Antiferromagnetic Metallic Oxide

Combining infrared reflectivity, transport, susceptibility, and several diffraction techniques, we find compelling evidence that CaCrO3 is a rare case of a metallic and antiferromagnetic transition-metal oxide with a three-dimensional electronic structure. Local spin density approximation calculations correctly describe the metallic behavior as well as the anisotropic magnetic ordering pattern of C type: The high Cr valence state induces via sizable pd hybridization remarkably strong next-nearest-neighbor interactions stabilizing this ordering. The subtle balance of magnetic interactions gives rise to magnetoelastic coupling, explaining pronounced structural anomalies observed at the magnetic ordering transition.

Ab Initio Calculations on the Magnetic Properties of Hydrogenated Boron Nitride Nanotubes

Ab initio local spin density approximation calculations were performed to study the magnetic properties of hydrogenated boron nitride nanotubes (H-BNNTs). It is found that the adsorption of a single H atom on the external surface of BNNT can induce spontaneous magnetization in the H-BNNTs, whereas no magnetism is observed when two H atoms are adsorbed on two neighboring N atoms or on two neighboring B and N atoms. However, spontaneous magnetization is also found in the H-BNNTs with two H atoms on two B atoms not next to each other, the further the better. This may be experimentally accessible when the coverage of H atoms adsorbed on the external surface of BNNTs is low. Defects produce spontaneous magnetization on BNNTs. When one or three H atoms are adsorbed on vacancy defects of BNNTs, the H-BNNTs are nonmagnetic, while magnetic H-BNNT can be obtained by two H atoms adsorbed on vacancy defects, which may be difficult to control experimentally. The key issue for magnetism is the existence of unpaired electrons, which can be experimentally realized by either low coverage of hydrogen atoms or making defects on perfect BNNTs. This indicates that it is possible to tune the magnetic properties of BNNTs by hydrogenation or defects, thus providing a new synthetic route toward metal-free magnetic materials.

Temperature-induced longitudinal spin fluctuations in Fe and Ni

We have developed an ab initio framework for calculating parameters of a high-temperature magnetic Hamiltonian. In the adiabatic approximation, this includes transverse and longitudinal magnetic excitation spectra on equal footing. The exchange interaction parameters of the Hamiltonian for bcc Fe and fcc Ni are determined from constrained local spin-density approximation calculations. Finite temperature magnetic properties of the resulting model Hamiltonian are then investigated by a Monte Carlo simulation technique. The calculated Curie temperatures and paramagnetic susceptibilities are in good agreement with experimental data for both metals. We demonstrate that the temperature-induced longitudinal spin fluctuations are important for high temperature properties such as susceptibility and magnetic specific heat.

Fermi surface changes due to localized–delocalized f-state transitions in Ce-115 and Pu-115 compounds

The current theoretical understanding of the electronic structures of the CeMIn 5 compounds (with M=Co, Rh, and Ir) and PuCoGa 5 and PuRhGa 5 is reviewed. Both the Ce-115 and Pu-115 compounds have in common that their f-electrons appear to be poised on the edge of a localization–delocalization boundary. We consider here the implications of this characteristic on the emergent electronic structure, addressing, in particular, the computed Fermi surfaces. In order to capture the electronic structures to the best as possible, we employ three different density-functional theory based computational approaches, viz. the local-spin density approximation (LSDA) for delocalized f-states, the open-core approach for localized f's, and the LSDA+ U approach for moderately localized f's. The Fermi surfaces of CeCoIn 5 and CeIrIn 5 are rather well described assuming delocalized 4f electrons. Conversely, the better description is obtained for CeRhIn 5 assuming a localized 4f state. For the Pu-115 compounds, LSDA calculations predict a rather two-dimensional Fermi surface. However, the Fermi surface of PuCoGa 5 computed with the around-mean field LSDA+ U scheme is also quite two-dimensional and, moreover, similar to the LSDA Fermi surface. Taking other available experimental data on PuCoGa 5 into account, it appears that the electronic structure of PuCoGa 5 is best described by the AMF-LSDA+ U approach with a Coulomb U of about 3 eV.

Fermiology of PuCoGa 5 and of related Pu-115 compounds

We report computational investigations of the electronic structures of the superconducting Pu-compounds PuCoGa 5 as well as of the non-superconducting compounds PuFeGa 5 and PuNiGa 5. To capture the localization behavior of the Pu 5f electrons, we apply two computational approaches, which are both rooted in the density-functional theory: the local spin-density approximation (LSDA) and the around mean field (AMF) LSDA + U approach. The latter is applicable to moderately localized 5f electrons while the former is applicable to delocalized 5f electrons. Our LSDA calculations show that the Fermi surfaces of the three Pu-115 compounds are sensitive to the amount of band filling, i.e., the number of electrons of the 3d element. Precisely at the electron filling corresponding to PuCoGa 5 the Fermi surface has a particularly two-dimensional shape. AMF–LSDA + U calculations (with a Coulomb U of about 3 eV and exchange J of 0.6 eV) lead to a non-magnetic ground state for PuCoGa 5, in which the 5f states are shifted to a higher binding energy, in better agreement with photoemission data. The Fermi surface of PuCoGa 5 computed with the AMF–LSDA + U approach is nonetheless rather two-dimensional and similar to the LSDA Fermi surface. The AMF–LSDA + U approach with a Coulomb U of ≈ 3 eV would thus predict an electronic structure for PuCoGa 5 in accord with several experimental data.

Spin waves of the spin‐polarized electron gas in semimagnetic quantum wells

AbstractSpin flip waves and spin density fluctuations of a two‐dimensional spin‐polarized electron‐gas in a semimagnetic Cd1–0.008Mn0.008Te quantum well are observed by Resonant Raman Scattering. Application of a magnetic field splits the spin subbands and a static spin polarization is induced. Wavevector and field experimental dispersions are very well reproduced by Local Spin Density Approximation calculations including recent Quantum Monte Carlo evaluation of coulomb correlations corrections. We show how to extract the spin polarization degree. A maximum value of 35% is deduced from measurements. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)