Linear Muffin-tin Orbital Method Research Articles

Substantial Cd–Cd Bonding in Ca6PtCd11: A Condensed Intermetallic Phase Built of Pentagonal Cd7and Rectangular Cd4/2Pt Pyramids

The novel intermetallic Ca6PtCd11 is orthorhombic, Pnma, Z = 4, with a = 18.799(2) Å, b = 5.986(1) Å, c = 15.585(3) Å. The heavily condensed network contains three types of parallel cadmium chains: apically strongly interbonded Cd7 pentagonal bipyramids, linear Cd arrays, and rectangular Cd4/2Pt pyramids. All of the atoms have 11-13 neighbors. Calculations by means of the linear muffin-tin orbitals method in the atomic spheres approximation indicate that some Cd-Cd interactions correspond to notably high Hamilton populations (1.07 eV per average bond) whereas the Ca-Ca covalent interactions (integrated crystal orbital Hamiltonian population) are particularly small (0.17 eV/bond). (Pt-Cd interactions are individually greater but much less in aggregate.) The Ca-Ca separations are small, appreciably less than the single bond metallic diameters, and unusually uniform (Δ = 0.14 Å). The Cd atoms make major contributions to the stability of the phase via substantial 5s and 5p bonding, which include back-donation of Cd 5s, 5p and Pt 5d into Ca 3d states in the principal bonding modes for Ca-Cd and Ca-Pt. Bonding Ca-Ca, Ca-Cd, and Cd-Cd states remain above EF, and some relative oxidation of Ca in this structure seems probable. Ca6PtCd11 joins a small group of other phases in which Cd clustering and Cd-Cd bonding are important.

High Pressure Band Structure, Metallization and Superconductivity of ZnSe and CdSe

The high pressure band structure, density of states, metallization, structural phase transition and superconductivity of cubic zinc blende type zinc selenide (ZnSe) and cadmium selenide (CdSe) are investigated using the full potential linear muffin-tin orbital (FP-LMTO) method. The ground state properties and band gap values are compared with the experimental results. The equilibrium lattice constant, bulk modulus and its pressure derivetive and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(EF)) gets enhanced after metallization, which leads to the superconductivity in ZnSe and CdSe. The superconducting transition temperatures (Tc) of ZnSe and CdSe are obtained as a function of pressure for NaCl structure. ZnSe and CdSe come under the class of pressure induced superconductors. When pressure is increased Tc increases in both compounds. The dependence of Tc on electron - phonon mass enhancement factor λ shows that ZnSe and CdSe are electron-phonon-mediated superconductors.

New Polar Intermetallic Phases RE2Zn5Tt (RE = La–Nd; Tt = Sn and Pb): Synthesis, Structure, Chemical Bonding, and Magnetic Properties

Reported are the synthesis, crystal structure, electronic structure, and magnetic properties of a series of zinc-rich ternary phases with formulas RE2Zn5Tt (RE = La-Nd; Tt = Sn and Pb). The structures of these compounds have been established by single-crystal and powder X-ray diffraction. They crystallize in the orthorhombic space group Cmcm (No. 63, LaRhSn2 structure type, Pearson symbol oC32). The most prominent structural feature is the trigonal-planar coordination of the Sn(Pb) atoms; the latter interconnect layers of Zn atoms to comprise a complex [Zn5Tt] polyanionic framework. The structural relationships between the structure of the title compounds and the EuIn4, La3Al11, and YIrGe2 structure types are highlighted. Temperature-dependent DC magnetization measurements indicate Pauli-like paramagnetism for La2Zn5Sn, while Ce2Zn5Sn, Pr2Zn5Sn, and Nd2Zn5Sn display Curie-Weiss behavior in the high-temperature regime. At cryogenic temperatures, the magnetic responses of Ce2Zn5Sn, Pr2Zn5Sn, and Nd2Zn5Sn appear to deviate from the Curie-Weiss law; however, no magnetic orderings could be observed down to 5 K. Theoretical considerations of the electronic structure on the basis of the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method are also presented and discussed.

First Principles Study of Electronic Structure and Magnetic Properties of TMH (TM = Cr, Mn, Fe, Co)

First principles calculations are performed using a tight-binding linear muffin-tin orbital (TB-LMTO) method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of transition metal hydrides (TMH) (TM = Cr, Mn, Fe, Co). The structural property, electronic structure, and magnetic properties are investigated. A pressure induced structural phase transition from cubic to hexagonal phase is predicted at the pressures of 50 GPa for CrH and 23 GPa for CoH. Also, magnetic phase transition is observed in FeH and CoH at the pressures of 10 GPa and 180 GPa, respectively.

Electronic structure, phonon spectra and electron–phonon interaction in ScB2

The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron–phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the ScB2 diboride were investigated from first principles using the fully relativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of electron–phonon spectral functions, electrical resistivity, cyclotron masses and extremal cross sections of the Fermi surface was achieved.

Structural Characterization of the Intermetallic Phase EuZnxIn4-x(x ≈ 1.1-1.2). Zn and In Site-Preferences in the BaAl4Structure-Type from Computational Analysis

, respectively. In this structure, the Eu atoms are situated at the center of 18-vertexFedorov polyhedra made of Zn and In atoms, where the 4 d site is preferentially occupied by In and the 4 e siteis occupied by randomly mixed Zn and In atoms. Theoretical investigations using tight-binding linear muffin-tin orbital (TB-LMTO) method provide rationale for the observed site preferences and suggest potentiallywider homogeneity range than the experimentally established for EuZn

Accurate determination of band gaps within density functional formalism

In this paper, we report an adaptation of the Harbola-Sahni (HS) exchange potential to the tight-binding linear muffin-tin orbital (TB-LMTO) method to determine band gaps (BGs) of solids accurately. We show that the electrostatic basis of derivation of the Harbola-Sahni potential allows this nonvariational approach to improve substantially over local-density approximation derived BGs, bringing them very close to experimental values. That the accuracy of the HS potential is directly responsible for the determination of correct BGs is demonstrated by performing similar calculations with an accurate model potential that too leads to BGs close to their experimental values. Moreover, ground-state properties like equilibrium lattice parameters and bulk moduli (BM) for various semiconductors like C, Si, AlN, AlP, BP, and 3C-SiC calculated with the HS approach are in close agreement with the experiments. The clear physical interpretation of HS potential leads us to suggest exploring its use for calculating various properties of solids.

Tm2.22Co6Sn20and TmLi2Co6Sn20stannides as disordered derivatives of the Cr23C6structure type

A new ternary dithulium hexacobalt icosastannide, Tm2.22Co6Sn20, and a new quaternary thulium dilithium hexacobalt icosastannide, TmLi2Co6Sn20, crystallize as disordered variants of the binary cubic Cr23C6 structure type (cF116). 48 Sn atoms occupy sites of m.m2 symmetry, 32 Sn atoms sites of .3m symmetry, 24 Co atoms sites of 4m.m symmetry, eight Li (or Tm in the case of the ternary phase) atoms sites of -3 symmetry and four Tm atoms sites of m3m symmetry. The environment of one Tm atom is an 18-vertex polyhedron and that of the second Tm (or Li) atom is a 16-vertex polyhedron. Tetragonal antiprismatic coordination is observed for the Co atoms. Two Sn atoms are enclosed in a heavily deformed bicapped hexagonal prism and a monocapped hexagonal prism, respectively, and the environment of the third Sn atom is a 12-vertex polyhedron. The electronic structures of both title compounds were calculated using the tight-binding linear muffin-tin orbital method in the atomic spheres approximation (TB-LMTO-ASA). Metallic bonding is dominant in these compounds, but the presence of Sn-Sn covalent dumbbells is also observed.

A Ferrimagnetic Zintl Phase Pr4MnSb9: Synthesis, Structure, and Physical Properties

A new valence precise Zintl phase, Pr4MnSb9, has been successfully synthesized by solid-state reaction at high temperature. The single-crystal X-ray diffraction data reveal its monoclinic symmetry in the space group C2/m (No. 12) with a = 24.12(2) Å, b = 4.203(3) Å, c = 15.67(2) Å, β = 98.05(1)°, and Z = 4. The structure is characterized by the covalent three-dimensional network constructed by two types of five-atom-wide Sb5(7-) ribbons that are joined by 6-fold coordinated Mn(3+) cations, through which the narrower three-atom-wide Sb3(5-) ribbons are attached as a tag, and interstitial Pr(3+) cations and single Sb(3-) anions locate within the tunnels. Its magnetic susceptibility and isothermal hysteresis suggest ferrimagnetic behavior. The electrical conductivity and Seebeck coefficient of the cold-pressed pellet suggest a semimetal feature that agrees with the spin-polarized calculation results using the tight-binding linear muffin-tin orbital (TB-LMTO) method.

From One to Three Dimensions: Corrugated ∞1[NiGe] Ribbons as a Building Block in Alkaline Earth Metal Ae/Ni/Ge Phases with Crystal Structure and Chemical Bonding in AeNiGe (Ae = Mg, Sr, Ba)

The new equiatomic nickel germanides MgNiGe, SrNiGe, and BaNiGe have been synthesized from the elements in sealed tantalum tubes using a high-frequency furnace. The compounds were investigated by X-ray diffraction both on powders and single crystals. MgNiGe crystallizes with TiNiSi-type structure, space group Pnma, Z = 4, a = 6.4742(2) Å, b = 4.0716(1) Å, c = 6.9426(2) Å, wR2 = 0.033, 305 F(2) values, 20 variable parameters. SrNiGe and BaNiGe are isotypic and crystallize with anti-SnFCl-type structure (Z = 4, Pnma) with a = 5.727(1) Å, b = 4.174(1) Å, c = 11.400(3) Å, wR2 = 0.078, 354 F(2) values, 20 variable parameters for SrNiGe, and a = 5.969(4) Å, b = 4.195(1) Å, c = 11.993(5) Å, wR2 = 0.048, 393 F(2) values, 20 variable parameters for BaNiGe. The increase of the cation size leads to a reduction of the dimensionality of the [NiGe] polyanions. In the MgNiGe structure the nickel and germanium atoms build a ∞(3)[NiGe] network with magnesium atoms in the channels. In SrNiGe and BaNiGe the ∞(1)[NiGe] ribbons are separated by strontium/barium atoms, whereas in the known CaNiGe structure the ribbons are fused to two-dimmensional atom slabs. The crystal chemistry and chemical bonding in AeNiGe (Ae = Mg, Ca, Sr, Ba) are discussed. The experimental results are reconciled with electronic structure calculations performed using the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method.

High-pressure structural behaviour of Cu0.5Fe0.5Cr2S4: An experimental and theoretical study

The structural behaviour of Cu0.5Fe0.5Cr2S4 has been studied experimentally and theoretically at pressures up to 44 GPa. The experiments are supported by density functional calculations using the full-potential linear muffin-tin orbital method for investigating ground state properties and high-pressure behaviour. We report here the first experimental and theoretical determinations of the bulk modulus: B0 = 106(2) GPa and B 0 0 = 4.0 (experimental), and B0 = 96 GPa and B

First-principles calculations of the elastic, and electronic properties of YFe2, NiFe2 and YNiFe4 intermetallic compounds

Based on first principles full potential linear muffin-tin orbital method within the local density approximation, we have studied the structural, elastic, electronic properties and the behaviour under pressure on the magnetic moments per atoms from 0 to 85GPa for YFe2, NiFe2 and YNiFe4 intermetallic. The magnetic per formula unit value and equilibrium lattice constant of YFe2 are calculated and compared with experimental data and theoretical results. However, this is the first predictive calculations for the structural and magnetic properties for NiFe2 and YNiFe4 compounds. From the computed elastic constants, theoretical value of Young’s modulus, Shear modulus, Poisson’s ratio and Lamé’s coefficients, sound velocities and Debye temperature are evaluated. Our results demonstrate that NiFe2, YFe2 in C15 phase and NiYFe4 in C15b phase are mechanically stable with the large bulk moduli B0=BVR for alloys containing atom Ni (NiFe2=224.7GPa and NiYFe4=192.0GPa). Finally, we have calculated the total and partial density of states for the three compounds. The partial density of states shows strong hybridization at Fermi level.

Origin of the polar Kerr rotation in ordered and disordered FePt multilayers

The electronic structure and the magneto-optical properties of ordered and disordered FePt multilayers have been calculated by means of the spin-polarized relativistic linear muffin-tin orbital (SPR-LMTO) method within both the local spin-density approximation (LSDA) and generalized gradient approximation (GGA). Both approximations lead to the same magneto-optical results. The ordered FePt magneto-optical properties have also been calculated within the linear augmented plane wave method and the results are in good agreement with the SPR-LMTO calculations. The complex Kerr angle for ordered and disordered FePt has been calculated for photon energies of up to 6eV and is found to be in a good agreement with experiment. Different structures in the optical conductivity and Kerr rotation as a function of the photon energy are analyzed and discussed. To show the microscopic origin of the strong Kerr rotation at some particular photon energies the symmetry character of the bands contributing to interband transitions together with with the interband electric dipole momentum matrix elements are analyzed in the whole Brillouin zone (BZ). This analysis showed that the assignment of the peaks is complex and cannot only be attributed to interband transitions along high symmetry BZ directions.

Electronic structure and optical properties of anatase doped with bismuth and carbon

The calculations of the electronic structure of pure anatase and the anatase doped with carbon and/or bismuth have been carried out using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method in the local spin density approximation with the inclusion of single-site Coulomb correlations (LSDA + U). The dielectric function, absorption coefficient, and refractive index have been calculated in the random phase approximation. It has been found that, upon doping, narrow bands of carbon and bismuth impurity states are formed in the band gap. The calculations of the optical absorption coefficient have demonstrated that the C,Bi-doping can lead to the absorption in the visible region and an enhancement of the absorption in the near-ultraviolet region. Therefore, the C,Bi-doping can increase the photocatalytic activity on the surface of doped anatase.

Electronic Structure and Thermodynamic Properties of the Cubic Antiperovskite Compound InNCe $$_{3}$$ 3 via First-Principles Calculations

Elastic, thermodynamic, electronic, and magnetic properties in the cubic antiperovskite InNCe\(_{3}\) compound are derived from the full-potential linear muffin-tin orbital method. From the computed elastic constants, theoretical values of Young’s modulus, the shear modulus, Poisson’s ratio, Lame’s coefficients, sound velocities, and the Debye temperature are evaluated. Analysis of the ratio between the bulk modulus and the shear modulus shows that InNCe\(_{3}\) is brittle in nature. The variations of elastic constants with pressure indicate that this compound possesses higher mechanical stability in the pressure range from 0 to 40 GPa. The electronic and magnetic properties of this compound are calculated by adding the Coulomb interaction \(U\) to improve the results.

Comparative study of the electronic structure, phonon spectra, and electron-phonon interaction of ZrB2and TiB2

The electronic structure, optical and x-ray absorption spectra, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron-phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the MB2 (M=Ti and Zr) diborides were investigated from first principles using the full potential linear muffin-tin orbital method. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of optical and x-ray absorption spectra, phonon spectra, electron-phonon spectral functions, electrical resistivity, cyclotron masses and extremal cross sections of the Fermi surface was achieved.

Thermodynamic functions of the heated electron subsystem in the field of cold nuclei

The paper presents electronic heat capacities and thermal pressures calculated for aluminum and tungsten at densities ρ0 ≤ ρ ≤ 2ρ0 in the case when the temperature of electrons is finite (a few electron-volts) and nuclei are cold. Calculations were done with the all-electron full-potential linear muffin-tin orbital method (FP-LMTO) and compared with data obtained with the Liberman's average-atom model and the Vienna Ab-initio Simulation Package code (VASP) which uses pseudopotentials. It is shown that results obtained with different approaches qualitatively agree within the ranges of electron temperatures and densities under consideration, and quantitatively agree within 10% in most cases.

Effect of p–d hybridization, structural distortion and cation electronegativity on electronic properties of ZnSnX2 (X=P, As, Sb) chalcopyrite semiconductors

Significant effects of p–d hybridization, structural distortion and cation-electro-negativity are found on band gap in ZnSnX2 (X=P, As, Sb). Our study suggests these compounds to be direct band gap semiconductors with band gaps of 1.23, 0.68 and 0.19eV respectively. Lattice constants, tetragonal distortion (η), anion displacement, bond lengths and bulk moduli are calculated by Density Functional Theory based on Tight binding Linear Muffin-Tin orbital method. Our result of structural properties is in good agreement with the available experimental and other theoretical results. Calculated band gaps also agree well with the experimental works within LDA limitation. Unlike other semiconductors in the group II–IV–V2, there is a reduction in the band gap of 0.22, 0.20 and 0.24eV respectively in ZnSnX2 (X=P, As, Sb) due to p–d hybridization. Structural distortion decreases band gap by 0.20, 0.12 and 0.10eV respectively. We find that cation electronegativity effect is responsible for increasing the band gap relative to their binary analogs GaInP2, InGaAs2 and GaInSb2 respectively and increment are 0.13, 0.04 and 0.13eV respectively.

Rhombohedrally Distorted γ-Au5–xZn8+y Phases in the Au–Zn System

The region of the Au-Zn phase diagram encompassing γ-brass-type phases has been studied experimentally from 45 to 85 atom % Zn. The γ phases were obtained directly from the pure elements by heating to 680 °C in evacuated silica tubes, followed by annealing at 300 °C. Powder X-ray and single-crystal diffraction studies show that γ-"Au(5)Zn(8)" phases adopt a rhombohedrally distorted Cr(5)Al(8) structure type rather than the cubic Cu(5)Zn(8) type. The refined compositions from two single crystals extracted from the Zn- and Au-rich loadings are Au(4.27(3))Zn(8.26(3))□(0.47) (I) and Au(4.58(3))Zn(8.12(3))□(0.3) (II), respectively (□ = vacancy). These (I and II) refinements indicated both nonstatistical mixing of Au and Zn atoms as well as partially ordered vacancy distributions. The structures of these γ phases were solved in the acentric space group R3m (No. 160, Z = 6), and the observed lattice parameters from powder patterns were found to be a = 13.1029(6) and 13.1345(8) Å and c = 8.0410(4) and 8.1103(6) Å for crystals I and II, respectively. According to single-crystal refinements, the vacancies were found on the outer tetrahedron (OT) and octahedron (OH) of the 26-atom cluster. Single-crystal structural refinement clearly showed that the vacancy content per unit cell increases with increasing Zn, or valence-electron concentration. Electronic structure calculations, using the tight-binding linear muffin-tin orbital method with the atomic-sphere approximation (TB-LMTO-ASA) method, indicated the presence of a well-pronounced pseudogap at the Fermi level for "Au(5)Zn(8)" as the representative composition, an outcome that is consistent with the Hume-Rothery interpretation of γ brass.

Structural and electronic properties of ScxAl1−xN: First principles study

The structural and electronic properties of ScxAl1−xN ternary semiconductor alloys are investigated in the rocksalt, zinc blend and wurtzite structures using the full potential linear muffin tin orbitals (FP-LMTO) method. The local density approximation (LDA) was used for the exchange and correlation energy density functional. In particular, the lattice constant, bulk modulus and band gap energies of ScN and AlN compounds and their ternary alloys ScxAl1−xN are calculated in rocksalt, zinc blend and wurtzite structures and discussed. A linear relationship has obtained for equilibrium lattice constants versus Sc concentration for rocksalt and zinc blend structures. The band gap is decreased with the increasing of Sc concentration in the rocksalt phase. For ZB-ScxAl1−xN, the band gap is the largest one at x=0.25 and changes from indirect to direct when x is more than 0.25.