Muffin-tin Orbital Atomic Sphere Approximation Research Articles

First-Principles Study of Electronic and Magnetic Properties of Anatase and its Role in Anatase-Mxene Nanocomposite

The electronic and magnetic properties of Titanium and one of its oxide Anatase are calculated by using Tight Binding Linear Muffin-Tin Orbital Atomic Sphere Approximation (TB-LMTO-ASA) method under Density Functional Theory (DFT). The lattice parameter, band structure, Density of States (DOS) and charge density distributions of Ti and TiO2 (Anatase) required for electronic structure are calculated respectively. The orbital contribution is analyzed by fat band structure; the d- orbital on conduction band and, s and p orbitals on valance bands. Consequently, their magnetic properties are checked. From our study, we found that the magnetic moments of Ti and TiO2 are found to be 2.2 μB and 0 respectively. The total Density of States for spin up and down electron have smaller difference in Ti and symmetric in TiO2 indicates that Ti slightly paramagnetic and Anatase is non magnetic in nature. The charge density plots reveals the concentration of electrons at the site under study. Anatase can be deposited onto Mxene to form Mxene-Anatase nanocomposite which has several excellent applications in the field of biosensors, biocompatible materials, energy storage devices, topological insulators etc.

Li9Al4Sn5as a new ordered superstructure of the Li13Sn5type

Alloys from the ternary Li-Al-Sn system have been investigated with respect to possible applications as negative electrode materials in Li-ion batteries. This led to the discovery of a new ternary compound, a superstructure of the Li13Sn5 binary compound. The ternary stannide, Li9Al4Sn5 (nonalithium tetraaluminium pentastannide; trigonal, P-3m1, hP18), crystallizes as a new structure type, which is an ordered variant of the binary Li13Sn5 structure type. One Li and one Sn site have -3m. symmetry, and all other atoms occupy sites of 3m. symmetry. The polyhedra around all types of atoms are rhombic dodecahedra. The electronic structure was calculated by the tight-binding linear muffin-tin orbital atomic spheres approximation method. The electron concentration is higher around the Sn and Al atoms, which form an [Al4Sn5]m- polyanion.

Noncollinear magnetism of Mn nanowires on Fe(1 1 0)

Magnetic properties of Mn linear nanochains on a bcc Fe(1 1 0) surface have been studied using the first-principles real space-linear muffin-tin orbital atomic sphere approximation (RS–LMTO–ASA) method. We have considered up to nine Mn atoms deposited on bcc Fe(1 1 0). Our ab initio calculations reveal the competition between the antiferromagnetic Mn–Mn and Mn–Fe couplings, presenting a behavior which is very different from Mn nanowires on Fe(0 0 1), as shown in a previous publication. Due to this competition and non-negligible Dzyaloshinskii–Moriya interaction, noncollinear magnetic structures are stabilized as ground states for the Mn nanochains on Fe(1 1 0).

Li4Ge2B as a new derivative of the Mo2B5 and Li5Sn2 structure types.

Binary and multicomponent intermetallic compounds based on lithium and p-elements of Groups III-V of the Periodic Table are useful as modern electrode materials in lithium-ion batteries. However, the interactions between the components in the Li-Ge-B ternary system have not been reported. The structure of tetralithium digermanium boride, Li4Ge2B, exhibits a new structure type, in the noncentrosymmetric space group R3m, in which all the Li, Ge and B atoms occupy sites with 3m symmetry. The title structure is closely related to the Mo2B5 and Li5Sn2 structure types, which crystallize in the centrosymmetric space group R-3m. All the atoms in the title structure are coordinated by rhombic dodecahedra (coordination number = 14), similar to the atoms in related structures. According to electronic structure calculations using the tight-binding-linear muffin-tin orbital-atomic spheres approximation (TB-LMTO-ASA) method, strong covalent Ge-Ge and Ge-B interactions were established.

Study of Electronic and Magnetic Properties of CuPd, CuPt, Cu<sub>3</sub>Pd and Cu<sub>3</sub>Pt: Tight Binding Linear Muffin-Tin Orbitals Approach

Electronic structure of ordered alloys CuPd, CuPt, Cu3Pd and Cu3Pt have been studied using Tight Binding Linear Muffin-Tin Orbitals Atomic Sphere Approximation (TB-LMTO-ASA). For the electronic properties, we have performed band structure calculations. Our findings show that all the systems considered are metallic in nature. To know the contribution of the orbitals in the bands, the system is analyzed via fat bands which reveal most of the contributions on valence band for CuPd, CuPt, Cu3Pd and Cu3Pt is from d-orbital and on conduction band is from s and p-orbitals. We have also checked the magnetic properties of the alloys. The density of states for spin up and spin down electrons have found to be same in each and every steps, showing non-magnetic nature of CuPd, CuPt, Cu3Pd and Cu3Pt.Journal of Institute of Science and Technology, 2014, 19(1): 137-144

Quaternary pnictides with complex, noncentrosymmetric structures. Synthesis and structural characterization of the new Zintl phases Na11Ca2Al3Sb8, Na4CaGaSb3, and Na15Ca3In5Sb12.

Three new Zintl phases, Na11Ca2Al3Sb8, Na4CaGaSb3, and Na15Ca3In5Sb12, have been synthesized by solid-state reactions, and their structures have been determined by single-crystal X-ray diffraction. Na11Ca2Al3Sb8 crystallizes with its own structure type (Pearson index oP48) with the primitive orthorhombic space group Pmn2(1) (No. 31). The structure is best viewed as [Al3Sb8](15-) units of fused AlSb4 tetrahedra, a novel type of Zintl ion, with Na(+) and Ca(2+) cations that solvate them. Na4CaGaSb3 also crystallizes in its own type with the primitive monoclinic space group Pc (No. 7; Pearson index mP36), and its structure boasts one-dimensional [GaSb3](6-) helical chains of corner-shared GaSb4 tetrahedra. The third new compound, Na15Ca3In5Sb12, crystallizes with the recently reported K2BaCdSb2 structure type (space group Pmc2(1); Pearson index oP12). The Na15Ca3In5Sb12 structure is based on polyanionic layers made of corner-shared InSb4 tetrahedra. Approximately one-sixth of the In sites are vacant in a statistical manner. All three structures exhibit similarities to the TiNiSi structure type, and the corresponding relationships are discussed. Electronic band structure calculations performed using the tight-binding linear muffin-tin orbital atomic sphere approximation method show small band gaps for all three compounds, which suggests intrinsic semiconducting behavior for these materials.

Magnetic properties of FexCo1−x nanochains on Pt(1 1 1) surfaces

The magnetic properties of FexCo1−x nanochains on Pt(1 1 1) were studied using the first-principles real-space linear muffin-tin orbital-atomic sphere approximation (RS-LMTO-ASA) method within the density functional theory. The relative amounts of Fe and Co atoms in a chosen nanochain were varied and several possible arrangements of the atomic species were taken into account. The results of the exchange interaction demonstrates ferromagnetic coupling for the nanowires. Our calculations of Fe and Co average magnetic moments reveal a large enhancement of both spin and orbital moments compared to Fe–Co films deposited on a Pt(1 1 1) surface. The trend for the orbital moments with respect to stoichiometry differs from all previous higher-dimensional Fe–Co alloys on Pt(1 1 1) studies.

CrZn17+δ (−0.75 ⩽ δ ⩽ 2.00): A partly disordered complex intermetallic compound

The γ-brass related phase CrZn17+δ(−0.75⩽δ⩽2.00) in the Cr–Zn binary system has been synthesized and the structure has been analyzed by powder and single crystal X-ray diffraction. The compound crystallizes in the cubic space group F4¯3m (216). The unit cell contains 400–403 atoms. The phase width arises due to a disorder phenomenon. The structure can be described as an arrangement of nested polyhedral units, centered at sites of high symmetry points. The phase melts incongruently at ∼744K. Electronic structure calculations, using the tight-binding linear muffin-tin orbital atomic spheres approximation (TB-LMTOASA) method on the model of ordered “Cr5Zn96” shows the presence of a pseudogap at the Fermi level in the electronic density of states curves.

The complex metal-rich boride Ti1+xRh2−x+yIr3−yB3 (x=0.68, y=1.06) with a new structure type containing B4 zigzag fragments: Synthesis, crystal chemistry and theoretical calculations

Polycrystalline samples and single crystals of the new complex boride Ti1+xRh2−x+yIr3−yB3 (x=0.68; y=1.06) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-Ray diffraction as well as EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase, which represents a new structure type containing trans zigzag B4 fragments as well as isolated boron atoms crystallizes in the orthorhombic space group Pbam (Nr. 55) with the lattice parameters a=8.620(1)Å, b=14.995(2)Å and c=3.234(1)Å. First-principles density functional theory calculations using the Vienna ab-initio simulation package (VASP) were performed on an appropriate structural model (using a supercell approach) and the experimental crystallographic data could be reproduced accurately. Based on this model, the density of states and crystal orbital Hamilton population (for bonding analysis) were calculated, using the linear muffin-tin orbital atomic sphere approximation (LMTO-ASA) method. According to these calculations, this metal-rich compound should be metallic, as expected. Furthermore, very strong boron–boron interactions are observed in the trans zigzag B4 fragment, which induce a clear differentiation of two types of metal–boron contacts with different strength. The observed three-dimensional metal–metal interaction is in good agreement with the predicted metallic behavior.

Gold Derivatives of Eight Rare-Earth-Metal-Rich Tellurides: Monoclinic R7Au2Te2 and Orthorhombic R6AuTe2 Types

Two series of rare-earth-metal (R) compounds, R(7)Au(2)Te(2) (R = Tb, Dy, Ho) and R(6)AuTe(2) (R = Sc, Y, Dy, Ho, Lu), have been synthesized by high-temperature techniques and characterized by X-ray diffraction analyses as monoclinic Er(7)Au(2)Te(2)-type and orthorhombic Sc(6)PdTe(2)-type structures, respectively. Single-crystal diffraction results are reported for Ho(7)Au(2)Te(2), Lu(6)AuTe(2), Sc(6)Au(0.856(2))Te(2), and Sc(6)Au(0.892(3))Te(2). The structure of Ho(7)Au(2)Te(2) consists of columns of Au-centered tricapped trigonal prisms (TCTPs) of Ho condensed into 2D zigzag sheets that are interbridged by Te and additional Ho to form the 3D network. The structure of Lu(6)AuTe(2) is built of pairs of Au-centered Lu TCTP chains condensed with double Lu octahedra in chains into 2D zigzag sheets that are separated by Te atoms. Tight binding-linear muffin-tin orbital-atomic sphere approximation electronic structure calculations on Lu(6)AuTe(2) indicate a metallic property. The principal polar Lu-Au and Lu-Te interactions constitute 75% of the total Hamilton populations, in contrast to the small values for Lu-Lu bonding even though these comprise the majority of the atoms. A comparison of the theoretical results for Lu(6)AuTe(2) with those for isotypic Lu(6)AgTe(2) and Lu(6)CuTe(2) provides clear evidence of the greater relativistic effects in the bonding of Au. The parallels and noteworthy contrasts between Ho(7)Au(2)Te(2) (35 valence electrons) and the isotypic but much electron-richer Nb(7)P(4) (55 valence electrons) are analyzed and discussed.

First-principles studies of complex magnetism in Mn nanostructures on the Fe(001) surface

The magnetic properties of Mn nanostructures on the Fe(001) surface have been studied using the noncollinear first-principles real space-linear muffin-tin orbital-atomic sphere approximation method within density-functional theory. We have considered a variety of nanostructures such as adsorbed wires, pyramids, and flat and intermixed clusters of sizes varying from two to nine atoms. Our calculations of interatomic exchange interactions reveal the long-range nature of exchange interactions between Mn-Mn and Mn-Fe atoms. We have found that the strong dependence of these interactions on the local environment, the magnetic frustration, and the effect of spin-orbit coupling lead to the possibility of realizing complex noncollinear magnetic structures such as helical spin spiral and half-skyrmion.

Redetermination of LaZn5based on single crystal X-ray diffraction data

The crystal structure of the already known binary title compound LaZn5 (lanthanum penta­zinc) (space group P6/mmm, Pearson symbol hP6, CaCu5 structure type) has been redetermined from single-crystal X-ray diffraction data. In contrast to previous determinations based on X-ray powder data [Nowotny (1942). Z. Metallkd. 34, 247–253; de Negri et al. (2008). Inter­metallics, 16, 168–178], where unit-cell parameters and assignment of the structure type were reported, the present study reveals anisotropic displacement parameters for all atoms. The crystal structure consists of three crytallographically distinct atoms. The La atom (Wyckoff site 1a, site symmetry 6/mmm) is surrounded by 18 Zn atoms and two La atoms. The coordination polyhedron around one of the Zn atoms (Wyckoff site 2c, site symmetry -6m2) is an icosa­hedron made up from three La and nine Zn atoms. The other Zn atom (Wyckoff site 3g, site symmetry mmm) is surrounded by four La and eight Zn atoms. Bonding between atoms is explored by means of the TB–LMTO–ASA (tight-binding linear muffin-tin orbital atomic spheres approximation) program package. The positive charge density is localized around La atoms, and the negative charge density is around Zn atoms, with weak covalent bonding between the latter.

Li12Cu12.60Al14.37: a new ternary derivative of the binary Laves phases

New ternary dodecalithium dodecacopper tetradecaaluminium, Li(12)Cu(12.60)Al(14.37) (trigonal, R ̅3m, hR39), crystallizes as a new structure type and belongs to the structural family that derives from binary Laves phases. The Li atoms are enclosed in 15- and 16-vertex and the Al3 atom in 14-vertex pseudo-Frank-Kasper polyhedra. The polyhedra around the statistical mixtures of (Cu,Al)1 and (Al,Cu)2 are distorted icosahedra. The electronic structure was calculated by the TB-LMTO-ASA (tight-binding linear muffin-tin orbital atomic spheres approximation) method. The electron localization function, which indicates bond formation, is mostly located at the Al atoms. Thus, Al-Al bonding is much stronger than Li-Al or Cu-Al bonding. This indicates that, besides metallic bonding which is dominant in this compound, weak covalent Al-Al interactions also exist.

Complete Titanium Substitution by Boron in a Tetragonal Prism: Exploring the Complex Boride Series Ti3−xRu5−yIryB2+x (0 ≤ x ≤ 1 and 1 < y < 3) by Experiment and Theory

Polycrystalline samples and single crystals of four members of the new complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silvery phases were structurally characterized by powder and single-crystal X-ray diffraction as well as energy- and wavelength-dispersive X-ray spectroscopy analyses. They crystallize with the tetragonal Ti(3)Co(5)B(2) structure type in space group P4/mbm (No. 127). Tetragonal prisms of Ru/Ir atoms are filled with titanium in the boron-poorest phase (Ti(3)Ru(2.9)Ir(2.1)B(2)). Gradual substitution of titanium by boron then results in the successive filling of this site by a Ti/B mixture en route to the complete boron occupation, leading to the boron-richest phase (Ti(2)Ru(2.8)Ir(2.2)B(3)). Furthermore, both ruthenium and iridium share two sites in these structures, but a clear Ru/Ir site preference is found. First-principles density functional theory calculations (Vienna ab initio simulation package) on appropriate structural models (using a supercell approach) have provided more evidence on the stability of the boron-richest and -poorest phases, and the calculated lattice parameters corroborate very well with the experimentally found ones. Linear muffin-tin orbital atomic sphere approximation calculations further supported these findings through crystal orbital Hamilton population bonding analyses, which also show that the Ru/Ir-B and Ru/Ir-Ti heteroatomic interactions are mainly responsible for the structural stability of these compounds. Furthermore, some stable and unstable phases of this complex series could be predicted using the rigid-band model. According to the density of states analyses, all phases should be metallic conductors, as was expected from these metal-rich borides.

Self-interaction correction in multiple scattering theory: application to transition metaloxides

We apply to transition metal monoxides the self-interaction corrected (SIC) local spindensity approximation, implemented locally in the multiple scattering theory within theKorringa–Kohn–Rostoker (KKR) band structure method. The calculated electronicstructure and in particular magnetic moments and energy gaps are discussed in reference tothe earlier SIC results obtained within the linear muffin-tin orbital atomic sphereapproximation band structure method, involving transformations between Bloch andWannier representations, in order to solve the eigenvalue problem and calculate the SICcharge and potential. Since the KKR method can be easily extended to treat disorderedalloys, by invoking the coherent potential approximation (CPA), in this paper we comparethe CPA approach and supercell calculations to study the electronic structure of NiO withcation vacancies.

Mediated resonance effect of the vanadium 3dstates on phase stability in theAl8V5γ-brass studied by first-principles FLAPW and LMTO-ASA electronic structure calculations

The mechanism for the stability of the ${\mathrm{Al}}_{8}{\mathrm{V}}_{5}\phantom{\rule{0.3em}{0ex}}\ensuremath{\gamma}$-brass containing 52 atoms in its cubic unit cell has been investigated by means of first-principles full-potential linearized augmented plane wave (FLAPW) and linearized muffin-tin orbital-atomic sphere approximation (LMTO-ASA) electronic structure calculations. The LMTO-ASA identified a deep valley at $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ above the Fermi level in its density of states (DOS) as arising from orbital hybridizations between V $3d$ and Al $3p$ states. On the other hand, the FLAPW revealed the V $3d$ states mediated resonance of electrons with different sets of lattice planes. The resonance involved is found to be substantial not only at ${\ensuremath{\mid}\mathbf{G}\ensuremath{\mid}}^{2}=18$ or {330} and {411} zones but also at those in the range $14\ensuremath{\leqslant}{\ensuremath{\mid}\mathbf{G}\ensuremath{\mid}}^{2}\ensuremath{\leqslant}30$. A comparison with the electronic structure of the CsCl-type AlV compound proved that the V $3d$ states mediated resonance occurs only in ${\mathrm{Al}}_{8}{\mathrm{V}}_{5}$ but not in AlV compound. The V $3d$ states mediated resonance is proved to result in a significant suppression of the $sp$-partial DOS over the energy range from the Fermi level up to $+2.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. A gain in the electronic energy has been attributed to the formation of highly condensed bonding states below the Fermi level, again caused by the V $3d$ states mediated resonance. It is also proposed that the ${\mathrm{Al}}_{8}{\mathrm{V}}_{5}$ is stabilized at $e∕a=1.94$ rather than $21∕13$ as is expected from the Hume-Rothery electron concentration rule.

Universal tight-binding model for transition metals: from bulk to cluster

A universal orthogonal tight-binding (TB) model is developed for transition metals, withspecial emphasis on spin-polarized self-consistent calculations. The parameters of the TBmodel are directly obtained from the ab initio bulk calculations within the linear muffin-tinorbital atomic sphere approximation method, without any fitting. With the environmentaldependence of the Hamiltonian included in the localized structure constants, the TB modelcan be reliably applied to various situations, from periodic bulk structures to smallclusters, for both pure metals and alloys. We have tested the model in spin-polarizedcalculations against ab initio results for small computational cell systems, andapplied the model to study the spin and orbital magnetism of some large clusters.

Experimental and theoretical investigations of the electronic structure of Ni–X (X = Al, Si, P) systems

For the stoichiometric compounds Ni–X (X=Si, Al, P), the X-ray photoelectron spectra of valence bands are obtained and calculations of their electronic structure are carried out by the tight-binding linear muffin-tin orbital atomic sphere approximation (TB-LMTO-ASA) method. A satisfactory agreement of the X-ray photoelectron spectra and the calculated density of states curves is obtained. It is shown that with the increase of the second component p-electrons, the hybridization of d(Me) and p(X) electrons decreases, the probability of d–p resonance increases and the contribution of p(X) states near E f increases too.

Element-specific magnetic moments from core-absorption magnetic circular dichroism of the doped Heusler alloyCo2Cr0.6Fe0.4Al

The magnetic circular dichroism (MCD) of core-level absorption (x-ray absorption spectroscopy, XAS) spectra in the soft x-ray region has been measured for the ferromagnetic Heusler alloy ${\mathrm{Co}}_{2}{\mathrm{Cr}}_{0.6}{\mathrm{Fe}}_{0.4}\mathrm{Al}$ at the Co, Fe, and Cr ${L}_{II,III}$ edges. The comparison of XAS spectra before and after in situ cleaning of polished surfaces revealed a pronounced selective oxidation of Cr in air. For clean surfaces we observed a MCD for all three elements with Fe showing the largest moment per atom. The MCD can be explained by the density of states of the $3d$ unoccupied states, predicted by linear muffin-tin orbital atomic sphere approximation. For Fe and Cr the orbital angular momentum component of the magnetic moment is considerably larger than the values reported for metallic alloys, whereas for Co a value close to its bulk value is observed. This observation is discussed in comparison with band structure calculations.

Investigation of the Hume–Rothery stabilization mechanism from ab initio band calculations for different electron compounds: Cu 5Zn 8 and Al–Mg–Zn, Al–Cu–Ru–Si approximants

The origin of the pseudogap formed across the Fermi level has been studied in relation to the Fermi surface–Brillouin zone interaction and the sp–d hybridization effect by performing the LMTO–ASA (Linear Muffin–Tin Orbital–Atomic Sphere Approximation) band calculations for the three electron compounds: the γ-phase Cu 5Zn 8 alloy, the free-electron-like Al 30Mg 40Zn 30 Frank–Kasper-type 1/1-1/1-1/1 approximant and the Al 68Cu 7Ru 17Si 8 Mackay–Icosahedral-type 1/1-1/1-1/1 approximant. We revealed that, in the free-electron-like Al–Mg–Zn approximant, the Fermi surface–Brillouin zone interaction is solely responsible for the formation of the pseudogap at the Fermi level. In the case of the γ-phase and the Al–Cu–Ru–Si approximant, where d-states are involved across the Fermi level, we have demonstrated that the Fermi surface–Brillouin zone interaction is still strong enough to produce the pseudogap near the Fermi level but that its depth and width are substantially enhanced by the sp–d hybridization effect which splits the d-states into the bonding and antibonding states across the Fermi level.