Linear Muffin-tin Orbital Atomic Sphere 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.

LiBC3: a new borocarbide based on graphene and heterographene networks.

Li-B-C alloys have attracted much interest because of their potential use in lithium-ion batteries and superconducting materials. The formation of the new compound LiBC3 [lithium boron tricarbide; own structure type, space group P-6m2, a = 2.5408 (3) Å and c = 7.5989 (9) Å] has been revealed and belongs to the graphite-like structure family. The crystal structure of LiBC3 presents hexagonal graphene carbon networks, lithium layers and heterographene B/C networks, alternating sequentially along the c axis. According to electronic structure calculations using the tight-binding linear muffin-tin orbital-atomic spheres approximations (TB-LMTO-ASA) method, strong covalent B-C and C-C interactions are established. The coordination polyhedra for the B and C atoms are trigonal prisms and for the Li atoms are hexagonal prisms.

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.

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.

Amendment of the Li-Bi Phase Diagram Crystal and Electronic Structure of Li2Bi

The phase diagram of the Li-Bi binary system was amended by x-ray analysis and differential scanning calorimetry. The formation of the binary compound Li2Bi was confirmed and its structure determined by x-ray single crystal diffraction. The Li2Bi compound crystallizes with the Mg2Ga structure type (space group P-62c, hP18, a = 8.0712(4) A, c = 6.8352(3) A). The analysis of the interatomic distances together with electronic structure calculations using the tight-binding linear muffin-tin orbital atomic spheres approximations (TB-LMTO-ASA) indicate the dominance of a metallic type of bonding, although there is a weak partially ionic bonding, caused by charge transfer from Li to Bi.

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 isothermal section of the phase diagram of Li–La–Ge ternary system at 400 °C

The isothermal section of the phase diagram of Li–La–Ge ternary system at 400 °C in the 30–100 at.% Ge concentration range was built and formation of seven ternary compounds were observed. For all ternary compounds: τ1–LiLa2Ge6−x (Cmmm space group, LiPr2Ge6 structure type), τ2–LiLaGe2 (Pnma, LiCaSi2), τ3–Li2La2Ge3 (Cmcm, Li2Ce2Ge3), τ4–Li8La7Ge10 (Cmmm, own structure type), τ5–Li12La11Ge16 (Immm, own structure type), τ6–Li4La3Ge4 (Immm, Gd3Cu4Ge4) and τ7–LiLa4Ge4 (Pnma, LiTm4Ge4) the crystal structures are known. The Li2La2Ge3, Li12La11Ge16, Li8La7Ge10 and Li4La3Ge4 ternary phases form the homologous series which is based on the simple Al2MgCu and AlB2 structure types. The crystal structures of LixLa5Ge3 phase, which formed by incorporation of lithium atoms into octahedral voids of La5Ge3 binary phase, was studied more precisely by X-ray powder diffraction and electrochemical investigation. According to electronic structure calculations using the tight-binding linear muffin-tin orbital-atomic spheres approximations (TB–LMTO–ASA) method the strong covalent Ge–Ge interactions were established.

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.

Polymorphism of Li2Zn3

Crystal structures of low- and high-temperature modifications of the binary phase Li(2)Zn(3) were determined by single-crystal X-ray diffraction techniques. The low-temperature modification is a disordered variant of Li(5)Sn(2), space group R\bar 3m (No. 166). The high-temperature modification crystallizes as an anti-type to Li(5)Ga(4), space group P\bar 3m1 (No. 164). Two polymorphs can be described as derivative structures to binary Li(5)Ga(4), Li(5)Sn(2), Li(13)Sn(5), Li(8)Pb(3), CeCd(2) and CdI(2) phases which belong to class 2 with the parent W-type in Krypyakevich's classification. All atoms in both polymorphs are coordinated by rhombic dodecahedra (coordination number CN = 14) like atoms in related structures. The Li(2)Zn(2.76) (for the low-temperature phase) and Li(2)Zn(2.82) (for the high-temperature phase) compositions were obtained after structure refinements. According to electronic structure calculations using the tight-binding-linear muffin-tin orbital-atomic spheres approximations (TB-LMTO-ASA) method, strong covalent Sn-Sn and Ga-Ga interactions were established in Li(5)Sn(2) and Li(5)Ga(4), but no similar Zn-Zn interactions were observed in Li(2)Zn(3).

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.

The effect of the positron distribution and electron–positron correlations on theelectron–positron momentum density for SiC

To interpret the data on positron annihilation in solids in terms of the electron momentumdensity, both the electron–positron interaction and the positron distribution have to beconsidered explicitly. In this work we discuss the influence of the shape of the positronwavefunction and electron–positron (e–p) correlations on the calculated e–p momentumdensity and lifetime of the positron in perfect SiC. It is shown that the form of the positrondistribution in the Wigner–Seitz cell has a considerable effect on the calculated annihilationcharacteristics. The results obtained within the independent particle model are comparedwith their counterparts incorporating e–p correlation functions locally and beyond the localdensity approximation. The calculations have been performed for SiC of 3C cubic(zinc-blende) structure within the linear muffin-tin orbital atomic sphere approximationmethod.

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.

Orbital angular momentum and interpretation of core-absorption magnetic circular dichroism on the band picture in Co-based Heusler alloysCo2YSn(Y=Ti,Zr,andNb)

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 alloys ${\mathrm{Co}}_{2}\mathrm{TiSn},$ ${\mathrm{Co}}_{2}\mathrm{ZrSn},$ and ${\mathrm{Co}}_{2}\mathrm{NbSn}.$ The many-peak structures which are clearly observed in the Co $2\stackrel{\ensuremath{\rightarrow}}{p}3d$ XAS-MCD spectra cannot be well explained by atomic multiplet calculations but are better explained by the Co $3d$ unoccupied states predicted by linear muffin-tin orbital atomic sphere approximation band structure calculations. The MCD spectra show an obvious contribution of the orbital angular momentum component to the magnetic moment in these alloys. The ratio between the orbital angular momentum and spin derived from the MCD spectra varies by more than a factor of 2 within these alloys. The mechanism of this variation is discussed in comparison with the band structure calculations.