Local Spin-density Functional Approximation Research Articles

Weyl fermions in antiferromagnetic Mn3Sn and Mn3Ge

The anomalous Hall effect in the noncollinear antiferromagnetic metals Mn3Ge and Mn3Sn has been observed after a theoretical prediction made by us (Kübler J. and Felser C., EPL, 108 (2014) 67001). The experimental values of the anomalous Hall conductivities (AHC) are large as are the theoretical values. Recently measured thermoelectric properties mirror the large AHC and clearly show that the transport is by quasiparticles at the Fermi energy. We here make an attempt to unravel the origin of the large AHC and show that both Mn3Sn and Mn3Ge host Weyl points, which were recently discovered in semimetals. For this purpose we determine the electronic structure ab initio in the local spin-density functional approximation. The Weyl points are found to occur below the Fermi energy and we argue that spots of large Berry flux (“hot spots”) that are seen at the Fermi surface are produced by the Weyl nodes.

Structural, Magnetic, and Magneto-Optical Properties of Fe/Cu Superlattices

The magnetic and magneto-optical properties of face-centered cubic (fcc)-Fe/nCu (001) superlattices are studied and compared with the fcc-Fe bulk structure. This is done using the method of all electron linearized augmented wave planes (FP L APW) in the local spin density functional approximation (DFT), implemented in the WIEN2k code, with the local spin density approximation for the exchange and correlation. As far as the magnetic properties are concerned, a significant increase of the magnetic moment of the iron atoms and the magnetic anisotropy energy (MAE) of the system is observed with increasing copper layers. A slight polarization occurs, with emergence of a small magnetic moment of copper atoms, due to the hybridization between the iron and copper orbitals. An antiferromagnetic phase of the system is observed, caused by the d states. The contraction film’s structure explains the continuous decay of the magnetic moment; therefore, the magneto-optical Kerr effect response could be investigated through the optical conductivity. In spite of their great magnetic moment, Kerr’s spectra are explained in terms of optical transitions and the MAE of the systems is calculated.

First-principles study for electronic structure and physical property of Co-based Heusler alloys

The statistical investigation of the physical property of Co-based Heusler alloys with the atomic composition or configuration dependence are carried out in first-principles approach. In particular, the electronic structure, magnetic moment and electrical resistivity due to disorder alloy effects of Co2MnAl1−zSiz (0.0 < z < 1.0) and Co2Mn1−yFeySi (0.0 < y < 1.0) with the L21, B2 and A2 structure are calculated by using the tight-binding linear muffin-tin orbital method combined with the coherent potential approximation based on the local spin-density functional approximation and by using the Kubo-Greenwood formula, respectively. The obtained results indicate that these properties of the Co-based Heusler alloys significantly depend on the atomic configuration and composition, especially, they are sensitive to the existence of the half-metallic property.

ELECTRONIC STRUCTURE AND MAGNETISM OF NixMn1-x ALLOYS

The electronic and magnetic structures of both bcc and fcc ordered Ni x Mn 1-x alloys, with x = 0, 0.25, 0.5, 0.75, and 1, are performed using the first principle linearized augmented plane-wave (LAPW) method within the framework of local spin-density functional approximation (LSDA). It is shown that fcc Ni x Mn 1-x with x = 1, 0.75 is ferromagnetic ordering, which is in good agreement with the experiments. At the equiatomic composition of Ni x Mn 1-x with x = 0.5, it is antiferromagnetic ordering. With the lower Ni composition, it presents ferrimagnetic and antiferromagnetic ordering, respectively. For bcc Ni x Mn 1-x with both rich Ni and rich Mn composition, however, it presents ferromagnetic and ferrimagnetic ordering, respectively. At the equiatomic Ni x Mn 1-x with x = 0.5, it presents ferromagnetic ordering.

Magnetic and electronic properties of double perovskites and estimation of their Curie temperatures byab initiocalculations

First-principles electronic structure calculations have been carried out on ordered double perovskites ${\text{Sr}}_{2}{B}^{\ensuremath{'}}{B}^{\ensuremath{''}}{\text{O}}_{6}$ (for ${B}^{\ensuremath{'}}=\text{Cr}$ or Fe and ${B}^{\ensuremath{''}}$ $4d$ and $5d$ transition-metal elements) with increasing number of valence electrons at the ${B}^{\ensuremath{''}}$ sites and on ${\text{Ba}}_{2}{\text{MnReO}}_{6}$ as well as ${\text{Ba}}_{2}{\text{FeMoO}}_{6}$. The Curie temperatures are estimated ab initio from the electronic structures obtained with the local spin-density functional approximation, full-potential generalized gradient approximation and/or the $\text{LDA}+U$ method (LDA, local density approximation; $U$, Hubbard parameter). Frozen spin spirals are used to model the excited states needed to evaluate the spherical approximation for the Curie temperatures. In cases where the induced moments on the oxygen were found to be large, the determination of the Curie temperature is improved by additional exchange functions between the oxygen atoms and between oxygen and ${B}^{\ensuremath{'}}$ and ${B}^{\ensuremath{''}}$ atoms. Pronounced systematics can be found among the experimental and/or calculated Curie temperatures and the total valence electrons of the transition-metal elements.

First-principles electronic structure and lattice dynamics of the giant dielectric compoundNa0.5Bi0.5Cu3Ti4O12

We report the results of an ab initio study of electronic, dielectric, and latticedynamical properties of high dielectric constant perovskite-derived oxideNa1/2Bi1/2Cu3Ti4O12. The calculations have been carried out within the local spin density functionalapproximation using norm-conserving pseudopotentials and a plane-wave basis. The groundstate is found to be an antiferromagnetic direct band gap semiconductor. Latticedynamical properties, such as Born effective charge tensors, dielectric permittivitytensors, and phonon frequencies at the Brillouin zone center were calculated usingdensity functional perturbation theory and found to be similar to the more studiedCaCu3Ti4O12 and CdCu3Ti4O12 compounds. The calculated electronic () and static (ϵ0≈150) dielectric constants indicate that the observed high dielectric constant is extrinsic in origin.The main contribution to the static dielectric constant is found to be due to a low frequency(50 cm−1) infrared-active mode which has a large mode effective charge.

Ab initio estimates of the Curie temperature for magnetic compounds

The local spin-density functional approximation is increasingly being used for materialsapplications such as predicting structural and magnetic properties. The recently aquiredability to model low-lying magnetic excitations like magnons is used for derivinguseful formulae to estimate the Curie (Néel) temperatures of magnetic compounds.Underlying this is Moriya’s unified approach, appropriately formulated for densityfunctional use. The theory is applied to the classical compounds FeNi, CoNi,FeNi3,CoNi3,and RhMn3 to establish a level of confidence, and to the Heusler compounds NiMnSb,Mn2VAl,Co2FeSi,Mn3Al,and Mn3Ga, which are presently studied with possible applications in mind for advanced spinelectronic devices.

Decompositional Incommensurate Growth of Ferrocene Molecules on a Au(111) Surface

Deviating from the common growth mode of molecular films of organic molecules where the adsorbates remain intact, we observe an essentially different growth behavior for metallocenes with a low temperature scanning tunneling microscope. Ferrocene molecules adsorb dissociatively and form a two layer structure. The top layer unit cell is composed of two tilted cyclopentadienyl (cp) rings, while the first layer consists of ferrocene molecules and cp-Fe complexes. Surprisingly a fourfold symmetry is observed for the top layer while the first layer displays threefold symmetry elements. It is this symmetry mismatch which induces an incommensurability between these layers in all except one surface direction. The top layer is weakly bonded and has an antiferromagnetic ground state as calculated by local spin density functional approximation.

Spin fluctuations in ferromagneticZrZn2

The magnetic properties of ferromagnetic ${\mathrm{ZrZn}}_{2}$ are calculated at zero and at finite temperatures. For this, use is made of the local spin-density functional approximation and an ab initio spin-fluctuation theory, which has its roots in the Ginzburg-Landau theory. In particular, the total energy, the magnetic moments, the density of states, and the band structure are obtained as functions of the pressure. Noncollinear spin arrangements yield the necessary information to calculate the pressure dependence of the nonuniform susceptibility at zero temperature as well as the Curie temperature and the Curie-Weiss susceptibility at high temperatures. The role of dissipation is discussed critically and comparison with recent experimental data for ${\mathrm{ZrZn}}_{2}$ shows satisfactory agreement.

Effects of local oxygen distortions on the electronic structure ofNaxCoO2

By using the pseudopotential method with the local spin-density functional approximation, the electronic band structure of ${\text{Na}}_{x}{\text{CoO}}_{2}$ is calculated for $x=0.25$, 0.5, 0.75, and $x=1$ in the presence of the structure relaxations. As the Na content increases, a phase transition is predicted from a wide-band ferromagnetic to a narrow-band paramagnetic metal. The itinerant ferromagnetism is strongly suppressed by the local distortions of the oxygens around the cobalts. Moreover, straining the ${\text{CoO}}_{2}$ layers corresponding to the hydrated superconductor ${\text{Na}}_{0.35}{\text{CoO}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}1.3{\mathrm{H}}_{2}\mathrm{O}$ strongly enhances the ferromagnetism.

Resonant photoemission spectroscopy of the quenched superconductivity system:Y1−xPrxBa2Cu3O7−δsingle crystals

The electronic structures of the quenched superconductivity system ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YPrBCO; $x=0,$ 0.4, 0.8) have been investigated by resonant photoemission spectroscopy (PES) measurements near the Pr $4\stackrel{\ensuremath{\rightarrow}}{d}4f$ absorption edge. With increasing x, PES data exhibit a binding-energy shift away from ${E}_{F}.$ The fine structures of YPrBCO $(x=0.8)$ are very similar to those of trivalent ${\mathrm{PrF}}_{3},$ providing evidence that Pr ions in YPrBCO are predominantly in Pr $3+$ states. Comparison of the PES spectra of YPrBCO with $x=0.8$ to the electronic structure for ${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ obtained by using the local spin-density functional approximation incorporating the Coulomb correlation shows good agreement in the bandwidths and the peak positions of the Cu d and O p states.

Non-Collinear Magnetic Moments of Five-Atom Transition-Metal Clusters

Non-collinear magnetic moments are calculated for trigonal bipyramid clusters, V 5 , Cr 5 , Mn 5 , Fe 5 , Co 5 , and Ni 5 by a simple method employing the locality of the local spin-density functional approximation and the discrete variational scheme. We discuss the magnetic properties of the transition-metal clusters with the bond lengths of 80%–100% of the crystalline interatomic distance. Parallel magnetic moments appear for the Ni, Co, and Fe clusters with almost all the bond lengths. Tilting magnetic moments also appear for the Co and Fe clusters in a certain bond length. Non-collinear magnetic arrangements appear for the Mn and Cr clusters, which change to antiparallel arrangements with decreasing bond length. Only an antiparallel alignment appears for the V cluster.

Ab initio Studies on Molecular Conductor (BEDSe-TTF)2[Fe(CN)5NO

In this paper the ab initio study using pseudopotential plane wave method with the local spin density functional approximation is presented for the molecular conductor (BEDSe-TTF)2[Fe(CN)5NO]. The mean electronic density distributions are obtained, and we find that the extended π orbital of the selenium does not affect the properties of material as assumed in other papers and the "side-by-side" type S...S interaction is the primary interaction between donors. From band structure calculations we analyze the influence of the NO groups on the electronic structure and magnetic properties of molecule. It is shown that the itinerant electrons important to electronic properties in these types of hybrids are delocalized electrons contributed by NO groups, instead of by the 3d electrons of Fe. Additionally, we have found that the localized magnetic moment is also contributed by the NO groups in this molecular conductor. From total energy calculations the molecular structure with the lowest energy is found due to the interaction between split spins, and the particular positions of the NO groups are obtained.

Electronic structures of electron-doped manganite: La0.7Ce0.3MnO3

Abstract The electronic structure of the electron-doped manganite La0.7Ce0.3MnO3 (LCeMO) has been investigated by performing the band calculations with the local spin-density functional approximation (LSDA), which are then compared to the photoemission spectroscopy (PES) data. In order to investigate the effect of the Mn 3d on-site Coulomb correlation on the electronic structure of LCeMO, we have calculated the Mn 3d partial density of states (PDOS) by performing the LSDA+U calculations. Our calculations show that the Mn 3d on-site Coulomb correlation accounts for the major features in the experimental PES spectra, such as the peak positions and the reduced spectral weight near the Fermi level.

First principles calculation of the interface state in fcc-Fe/Cu(111)

The interfacial properties of fcc-Fe/Cu(111) superlattices are investigated by the first principles all-electron linearized augmented plane wave method in the local spin-density functional approximation. For the paramagnetic phase an interface state located at 2.61 eV below the Fermi level at the K ̄ point of the two-dimensional Brillouin zone is obtained and it develops extending along the K ̄ − Γ ̄ direction. This is consistent with the experimental observation.

Metastable rhombohedral Fe phase formed in Fe/Sb multilayers and its magnetic properties

Fe/Sb multilayer films with various Fe and Sb layer thicknesses were prepared by vapor deposition. A metastable rhombohedral Fe phase was formed in the Fe/Sb multilayered films, when the Fe layer thickness was of 1.7 nm and the Sb layer thickness was of 10 nm. In an opposite condition, a metastable bcc Sb phase was obtained, when the Fe layer was thicker than 4 nm and the Sb layer was thinner than 2.5 nm. Interestingly, the metastable rhombohedral Fe exhibited ferromagnetic behavior and its average magnetic moment was as high as $1.52{\ensuremath{\mu}}_{B}.$ The magnetic behavior and electronic and magnetic structures of the rhombohedral Fe were calculated by the first-principles all-electron linearized augmented plane-wave method (LAPW) within the local spin-density functional approximation. The difference between the calculation of the Fe magnetic-moment amplitude $(3.32{\ensuremath{\mu}}_{B})$ and the experimental determination $(1.52{\ensuremath{\mu}}_{B})$ was discussed in terms of the presence of dead layers at the Fe/Sb interfaces.

Relative stabilities, bulk moduli and electronic structure properties of different ultra‐hard materials investigated within the local spin density functional approximation

The relative stabilities of the following phases: graphite-C3N4, α-C3N4, β-C3N4, cubic-C3N4 and pseudo-cubic-C3N4 have been determined using density functional theory in its local density approximation. In particular three calculational methods were imployed: augmented spherical wave, linear muffin-tin orbitals and full-potential linearized augmented plane-wave. The main objective of this work was the prediction of the hardness for a series of C3N4 phases (α, β, cubic and pseudo-cubic) as well as for the cubic BN (c-BN) structure. To this purpose total energy calculations were performed for different unit cell volumes and the resulting data were fitted to a polynomial function in order to determine the equilibrium lattice constants (aeq and ceq), bulk moduli (B0) and pressure derivatives (B0′). Even though the different methods do not produce comparable energy trends, all methods are in agreement in predicting equilibrium volume, bulk modulus and pressure derivatives. Further, for the graphite-based structures the influence of hybridisation on the chemical bonding and stability is discussed in terms of the site projected densities of states as well as the crystal orbital overlap population. For the hexagonal and orthorhombic phases the electronic properties are also discussed by means of a density of states analysis.

First-principles study of structural stability and electronic properties of Sb/GaSb(111) semimetal–semiconductor superlattice

The structural stability and electronic properties of a (Sb2)2/(GaSb)2(111) semimetal–semiconductor superlattice are investigated by a first-principles all-electron linearized augmented plane-wave method within the local spin density functional approximation. When bulk values are used the two interfacial distances D1 and D2 are energetically unfavorable. The fully optimized structure shows that the bond lengths of Sb–Ga and Sb–Sb at interfaces are 1.3% and 2.8% longer than their bulk values, respectively. Further electronic band calculations of the stable (Sb2)2/(GaSb)2(111) superlattice show that the system has semimetallic behavior. A p-like interface band is observed below the Fermi level.

Orbital magnetic moment enhancement at surfaces and interfaces within the framework of the local density approximation+U method

Stimulated by MCXD measurements, the determination of orbital magnetic moments, ML, at surfaces and interfaces has become a subject of strong interest. We combine the rotationally invariant local density approximation (LDA)+U total energy functional with a relativistic self-consistent spin-polarized version of the total energy full-potential linearized augmented plane wave method in order to determine ML at surfaces and interfaces. As illustration, the method is applied to Co overlayers on Cu(001). We find an enhancement of the Co orbital magnetic moment in LDA+U calculations in comparison with local spin density functional approximation (LSDA) results. ML as a function of magnetic Co-film thickness is analyzed. The ML/MS ratio is calculated to be different for different Co layers (i.e., interface, surface, or remaining Co layers) in Co/Cu(001), and is shown to be dependent on the Co overlayer thickness. Finally, the use of LDA+U is shown to give ML/MS in better agreement with MCXD data than does LSDA.

Symmetry properties of intra-atomic spin and angular momentum densities: application to

We consider the formation of the atomic spin and orbital moments in the framework of the local spin-density functional approximation by examining and exhibiting the symmetry properties of the intra-atomic spin and angular momentum densities, focusing on general principles, and elaborating by means of the realistic example of which is a noncollinear ferromagnet. We expose the role of the symmetry properties in determining the intra-atomic noncollinearity of the spin and orbital moments, which we connect with the inter-atomic configurations of the atomic moments.