Tight-binding Linear Muffin-tin Orbital Atomic Spheres 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.

Role of magnetism in the stability of the high-entropy alloy CoCrFeMnNi and its derivatives

Multiprincipal element alloys, called high-entropy alloys represent a promising group of materials. They possess unique mechanical or electrical properties, which provide a wide range of potential applications. In general, mechanical or electrical properties of a material are influenced by the magnetic behavior. Therefore, in our work, we are exploring magnetic behavior of so-called ``Cantor alloy'' CoCrFeMnNi and its molybdenum based derivatives. Mo alloys were studied not only to carefully describe their properties but also to probe the magnetic behavior of the parent alloy by adding a nonmagnetic element. Based on ab initio calculations using the TB-LMTO-ASA (tight-binding linear-muffin-tin-orbital atomic-sphere approximation) method within CPA (coherent-potential approximation), we have found the ground-state magnetic structures of a particular alloy. We deal with various magnetic structures including complex structures beyond the simple FM or DLM phases. We show the influence of the presence of a particular element on the magnetic properties. It includes, e.g., magnitudes of magnetic moments or preferred magnetic phases. The calculations were extended by studying the magnetic exchange interaction employing the Liechtenstein formula. We clearly show the contribution of each element to the magnetism as a function of the composition or crystal structure. We provide a thorough description of magnetic behavior in the mentioned compounds.

Dependence of magnetisation and magnetocrystalline anisotropy on site distribution of alloying elements in RE-TM phases with ThMn12 structure

The effect of site disorder (originating from the presence of substitutional atoms) on intrinsic magnetic properties of intermetallic phases derived from the ThMn12-type crystal structure has been studied using the tight-binding linear-muffin-tin-orbital atomic-sphere approximation (TB-LMTO-ASA) method of density functional theory (DFT). The focus was put on the analysis of magnetisation and magnetocrystalline anisotropy in 42 inequivalent configurations that differed in their arrangements of the substitutional atoms. The first-order anisotropy constant K1 turns out to be far more sensitive to the site occupancy than the magnetisation M. Addition of light interstitial atoms B, C or N gives rise to much higher K1 values but the same range of scattering is retained. As the anisotropy constant K1 is strongly increased by interstitial atoms, the influence of the atomic disorder is less pronounced for these systems.

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.

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.

Ab initio screening methodology applied to the search for new permanent magnetic materials

In this paper a computational high-throughput screening (HTS) approach to the search for alternative permanent magnetic materials is presented. Systems considered for a start are binary intermetallic compounds composed of rare-earth (RE) and transition metal (TM) elements. With the tight-binding-linear muffin-tin-orbital-atomic-sphere-approximation (TB-LMTO-ASA) method of density functional theory (DFT) a variety of RE–TM intermetallic phases is investigated and their magnetic properties are obtained at rather low computational costs. Next, interstitial elements such as boron, carbon and nitrogen in these phases are considered. For promising candidate phases with high and stable spontaneous ferromagnetic polarization, the calculated local magnetic moments and exchange coupling parameters, as obtained from TB-LMTO-ASA calculations, are then used for Monte Carlo simulations to identify candidates with sufficiently high Curie temperatures (Tc). Finally, magnetocrystalline anisotropy constants (K1) of the most promising candidate phases are calculated with accurate, potential-shape-unrestricted DFT calculations using the Vienna ab initio simulation package. The computational HTS procedure is illustrated by results for a selection of hard-magnetic RE–TM phases like RETM5, RE2TM17 and RE2TM14B.

On the Structural Chemistry of γ‐Brasses: Two Different Interpenetrating Networks in Ternary F‐Cell Pd–Zn–Al Phases

Novel ternary phases, (Pd(1-x)Zn(x))(18)(Zn(1-y)Al(y))(86-delta) (0<or=x<or=0.162, 0.056</=y<or=0.088, 0<or=delta<or=4), which adopt a superstructure of the gamma-brass type (called gamma'-brass), have been synthesized from the elements at 1120 K. Single-crystal X-ray structural analysis reveals a phase width (F43m, a=18.0700(3)-18.1600(2) A, Pearson symbols cF400-cF416), which is associated with structural disorder based on both vacancies as well as mixed site occupancies. These structures are constructed of four independent 26-atom gamma-clusters per primitive unit cells and centered at the four special positions A (0, 0, 0), B (1/4, 1/4, 1/4), C (1/2, 1/2, 1/2) and D (3/4, 3/4, 3/4). Two of these, centered at B and C, are completely ordered Pd(4)Zn(22) clusters, whereas the other two, centered at A and D, contain all structural disorder in the system. According to our single-crystal X-ray results, Al substitutions are restricted to the A- and D-centered clusters. Moreover, the outer tetrahedron (OT) site of the 26-atom cluster at D is completely vacant at the Al-rich boundary of these phases. Electronic structure calculations, using the tight-binding linear muffin-tin orbital atomic-spheres approximation (TB-LMTO-ASA) method, on models of these new, ternary gamma'-brass phases indicate that the observed chemical compositions and atomic distributions lead to the presence of a pseudogap at the Fermi level in the electronic density of states curves, which is consistent with the Hume-Rothery interpretation of gamma-brasses, in general.

The study of the atomic and electronic structures of liquid copper

In the work, the investigation of the atomic and electronic structure of liquid copper has been conducted using the molecular dynamics (MD) modeling method and the method of band calculation tight-binding linear muffin-tin-orbital atomic sphere-approximation (TB-LMTO-ASA) method. The experimental study of the electronic structure has been performed with the use of the 30-cm X-ray electronic magnetic spectrometer. The theoretical and experimental results of studying the electronic structure of liquid copper are in a good agreement. In the liquid state, a strong hybridization of d-electrons with p-electrons of copper atoms is observed which influences the shape of the valence bands and the curves of the total and d-partial DOS.

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.

Theoretical studies on cerium nickel aluminides: polar intermetallics with heavy fermion behavior

The electronic structures of Ce 4Ni 6Al 23, CeNiAl 4, CeNi 2Al 5, CeNiAl and CeNi 4Al have been calculated using the TB-LMTO-ASA (tight-binding, linear muffin-tin orbital, atomic-spheres approximation) approach to probe relationships between chemical bonding and physical properties in this series of intermetallic compounds. Analysis from crystal orbital Hamilton populations (COHP) reveal that the Al-rich compounds may be considered as “polar intermetallic” because the Fermi level coincides to the separation of bonding and antibonding states of the Ni–Al framework. On the other hand, although the densities of states (DOS) of CeNiAl suggest “polar intermetallic” behavior, the bonding is more complex. Finally, the Ni-rich example, CeNi 4Al, has significant Ni-3 d character at the Fermi level. The results of these calculations are also discussed in connection with heavy fermion or possible valence fluctuation behavior observed for some of these intermetallic compounds: those showing exceptional properties also exhibit significant “lattice covalency” between Ce and the Ni–Al nets.

Crystallographic, electronic and magnetic studies of Ce 4Ni 6Al 23: a new ternary intermetallic compound in the cerium–nickel–aluminum phase diagram

The Al-rich portion of the ternary Ce–Ni–Al has been investigated and a new ternary phase of composition Ce 4Ni 6Al 23 has been found. This compound crystallizes in the monoclinic space group C2/ m with the cell parameters a=16.042(8), b=4.140(4), c=18.380(8) Å and β=113.24(5)°. The structure has been determined by single crystal X-ray diffraction. The local environment of Ni and Ce is close to what is observed in the CeNi 2Al 5 and CeNiAl 4 structures. Band structure calculations, using the tight-binding–linear muffin-tin orbital–atomic-spheres approximation (TB-LMTO-ASA) method, have been performed to understand the electronic structure of Ce 4Ni 6Al 23 and the results are discussed in connection with those two other Ce–Ni–Al intermetallic compounds, which possess heavy-fermion behavior. Magnetic and heat capacity measurements have also been measured to analyze the low-temperature magnetic behavior of this new compound.

XPS-studies of the electronic structure of Fe–X (X=Al, Si, P, Ge, Sn) systems

For the stoichiometric compounds FeSi, FeGe, FeSn, FeAl, and FeP the X-ray photoelectron spectra of valence bands are obtained and the calculations of their electronic structure are carried out by the full-potential linear muffin–tin–orbital method (FP-LMTO) and by the tight-binding linear muffin–tin–orbital atomic sphere-approximation method (TB-LMTO-ASA). A satisfactory agreement of the X-ray photoelectron spectra and the calculated density of states curves is obtained. The comparison of the experimental spectra with the calculated curves shows that if the second component (X) of an alloy belongs to the same (IVth) group of the periodic table, the p–d hybridization is maximum in the alloy FeSi and decreased with the increase in the atomic radius (atomic number) of X(Ge, Sn). If X belongs to the same (IIIrd) row of the periodic table, then the p–d hybridization is maximum in FeAl and decreased with the increase in the number of p electrons of X(Si, P).