Linear Muffin-tin Orbital Method Research Articles

Structural, elastic, thermodynamic and electronic properties of LuX (X = N, Bi and Sb) compounds: first principles calculations

ABSTRACTThe structural, electronic, elastic and thermodynamic properties of LuX (X = N, Bi and Sb) based on rare earth into phases, Rocksalt (B1) and CsCl (B2) have been investigated using full-potential linearized muffin-tin orbital method (FP-LMTO) within density functional theory. Local density approximation (LDA) for exchange-correlation potential and local spin density approximation (LSDA) are employed. The structural parameters as lattice parameters a0, bulk modulus B, its pressure derivate B’ and cut-off energy (Ec) within LDA and LSDA are presented. The elastic constants were derived from the stress–strain relation at 0 K. The thermodynamic properties for LuX using the quasi-harmonic Debye model are studied. The temperature and pressure variation of volume, bulk modulus, thermal expansion coefficient, heat capacities, Debye temperature and Gibbs free energy at different pressures (0–50 GPa) and temperatures (0–1600 K) are predicted. The calculated results are in accordance with other data.

Electronic and magnetic properties at rough alloyed interfaces of Fe/Co on Au substrates: An augmented space study**Project supported by the INSPIRE Program Division, Department of Science and Technology, India.

We studied the interface electronic and magnetic properties of Fe/Co deposited on Au substrate and researched the effects of roughness at the interfaces within augmented space formalism (ASF). The full calculation is carried out by recursion and tight-binding linear muffin tin orbital (TB-LMTO) methods. The amount of roughness is different at different atomic layers. The formalism is also applied to sharp interface, when interdiffusion of atoms is negligible. Our results of one monolayer transition metal agree with other reported results. A realistic rough interface is also modeled with three and four monolayers of transition metals, deposited on Au substrates.

Electronic, magnetic, and optical characteristics of half-semiconductor double perovskite oxide Sr2CrOsO6 governed by 3d ([formula omitted])–5d ([formula omitted]) antiferromagnetic coupling

In this study, motivated by observations of the remarkable magnetic insulating nature and high Curie temperature (TC=725K) of double perovskite oxide Sr2CrOsO6, the electronic, magnetic, and optical characteristics of Sr2CrOsO6 were determined using the full potential linear muffin-tin orbital method according to density functional theory. The spin-orbit coupling contribution was included in the local spin density approximation (LSDA) and generalized gradient approximation (GGA). In addition, the Coulomb repulsion (U) and Hund’s exchange (J) energies were considered in both methods (LSDA+U and GGA+U). Full structural optimization confirmed that the ground state of Sr2CrOsO6 is face-centered cubic (Fm-3m symmetry). Calculations predicted that Sr2CrOsO6 is ferrimagnetic half-semiconductive (HSC) due to the vertical hopping of t2g electrons via antiferromagnetic coupling [Cr3+ (t2g3↑)–O (2pπ)–Os5+ (t2g3↓)], which agreed with the experimental results. The HSC energy-gaps originate from the splitting of three partially occupied Os5+ (5d) bands into two fully filled bands and one empty spin-down band. The real ε1(ω) and imaginary ε2(ω) parts of the dielectric function ε(ω) and energy-loss spectrum L(ω) were calculated, analyzed, and compared with the electronic results.

Electronic and structural properties of rare earth pnictides

Abstract In the present paper structural and electronic properties of rare earth pnictides have been presented. The present calculation has been performed using self-consistent tight binding linear muffin tin orbital (TB-LMTO) method within the local density approximation (LDA). The studied compounds undergo a structural phase transition from NaCl-type structure to CsCl-type structure. The electronic band structure and density of states of the pnictides have been reported. The equilibrium lattice parameter a (Å), bulk modulus B (GPa), number of f-states at the Fermi level Nf (states/Ry cell) and volume collapse of AmBi and CmBi have also been reported. The calculated equilibrium structural parameters are in good agreement with the available experimental results.

Electronic and optical properties of defect CdIn2Te4 chalcopyrite semiconductor: A first principle approach

We present detailed study of structural, electronic and optical properties of CdIn2Te4 compound. The calculations are carried out using Density Functional theory based Tight Binding Linear Muffin Tin Orbital method. The compound is found to be direct band gap semiconductor with a band gap of 1.03 eV. The band gap is within the limit of LDA underestimation. The calculated structural parameters agree well with the available experimental values. We find a decrements of 9.6% in band gap and significant effects on overall electronic and optical properties due to structural distortions. These effects on optical properties come mainly from the change in transition probability. An-isotropic nature of optical properties get enhanced due to structural distortion. The Calculated real & imaginary parts of dielectric constant and static dielectric constant agree well with the available experimental result.

First-Principles Study of Electronic, Magnetic, and Optical properties of the Intermetallic Compounds Ni 3 Mn Doped with Al

In this paper, we have calculated the electronic, magnetic, and optical properties of Ni3Mn1 − xAlx (x = 0, 0.25, 0.50, 0.75), using a spin-polarized scalar relativistic linear muffin-tin orbital (SPR-LMTO) method within density functional theory (DFT). The spin–orbit coupling was included as a perturbation in the self-consistent iterations. In our calculations for densities of states, we have used in all alloys the energy (E) range from −10 to + 10 eV. And for the optical spectra in all alloys, we have used the same energy range from 0.083 to 5.640 eV. In this work, we have discussed the effect of Al substitution on the electronic, magnetic, and optical properties of Ni3Mn intermetallics. We have calculated the coefficient of electronic specific heat, γ, for all these alloys; the values obtained are much larger compared to those in the constituent metals. We have found that the Al-doped Ni3Mn maintains the ferromagnetic character and leads to a decrease in the local and total magnetic moments but improves the conductivity. Qualitatively, the line shape of the theoretical optical conductivity coincides well with the experimental data. The magnetic moments per formula unit are found to be in good agreement with observed theoretical and experimental values.

Structural, electronic, elastic, optical and thermodynamic properties of copper halides CuCl, CuBr and their ternary alloys CuCl1−xBrx (0.0 ≤ x ≤ 1.0) using full-potential linear muffin-tin orbital (FP-LMTO) method

The structural, electronic, elastic, and thermodynamic properties of alloy CuCl1−xBrx in B3 (zinc blend) phase are investigated to investigate the effect of substitution of Br in CuCl in the range 0≤x≤1. For this purpose, first-principal calculations are used via the full-potential linear muffin-tin orbital (FP-LMTO). The exchange and correlation energy is described in the generalized gradient approximation (GGA). The effect of composition on lattice constant, bulk modulus and band gap is investigated. The concentration dependence of the electronic band structure and the direct-indirect band gap structures are also investigated. Using the approach of Zunger and co-workers, the microscopic origins of band gap bowing parameter have been interpreted. The refractive index, electron (hole) and valence effective masses are also calculated. Furthermore, thermodynamic stability of CuCl1−xBrx ternary alloys is studied by calculating the excess enthalpy of mixing ΔHm as well as the phase diagram.

First-principles calculation of band-gaps reduction in GaAsN alloys and (110) growth axis GaAs/GaN superlattice

First-principles calculations are performed to study the structural and electronic properties of GaAs and GaN zinc-blende/zinc-blende superlattices using the full potential linear muffin-tin orbitals method in its plane wave approximation which enables an accurate treatment of the interstitial regions. The choice of this method ensures the present work to be free from adjustable parameters and enabled us to perform a microscopic study. The results for GaAs/GaN superlattices with both (001) and (110) growth axis are investigated and compared. We have found that bowing, which is known to occur for ternary GaAsN dilute nitrides, is absent from GaAs/GaN “dilute nitride” of (001) growth axis superlattices for N concentrations beyond 7%, but it can be obtained in the (110) system.

Ab initio study of energetics and magnetism of sigma phase in Co–Mo and Fe–Mo systems

We analyse, from first-principles, the energetics and magnetic ordering of sigma phases in Co–Mo and Fe–Mo systems. Total energy differences between the sigma phase and Standard Element Reference (SER) structures are calculated in the whole concentration range at equilibrium volumes by means of the linear muffin-tin orbitals method in the atomic-sphere approximation (LMTO-ASA), the full-potential linearised augmented-plane waves (FLAPW) method and the pseudopotential approach. They are compared with the enthalpy of formation of sigma phase obtained from the phase equilibria calculations at higher temperature based on the semiempirical CALPHAD (CALculation of PHAse Diagram) method. It turns out that the binary sigma phases are more stable than the weighted average of the sigma phase of elemental constituents and that this stability for Fe–Mo is higher than for Co–Mo. On the other hand it was found that the binary sigma phases do not exhibit any stability with respect to the weighted average of the SER structures. The magnetic configurations in all systems are investigated and the stabilizing effect of magnetic order in sigma phase at 0 K is presented. It turns out that the atomic magnetic moment strongly depends on the type of occupied sublattice and total composition of the alloy.

Nonlocal torque operators inab initiotheory of the Gilbert damping in random ferromagnetic alloys

We present an ab initio theory of the Gilbert damping in substitutionally disordered ferromagnetic alloys. The theory rests on introduced nonlocal torques which replace traditional local torque operators in the well-known torque-correlation formula and which can be formulated within the atomic-sphere approximation. The formalism is sketched in a simple tight-binding model and worked out in detail in the relativistic tight-binding linear muffin-tin orbital (TB-LMTO) method and the coherent potential approximation (CPA). The resulting nonlocal torques are represented by nonrandom, non-site-diagonal and spin-independent matrices, which simplifies the configuration averaging. The CPA-vertex corrections play a crucial role for the internal consistency of the theory and for its exact equivalence to other first-principles approaches based on the random local torques. This equivalence is also illustrated by the calculated Gilbert damping parameters for binary NiFe and FeCo random alloys, for pure iron with a model atomic-level disorder, and for stoichiometric FePt alloys with a varying degree of L10 atomic long-range order.

Ab initio calculations of structural, elastic, electronic and thermodynamic properties of the cerium filled skutterudite CeRu4P12 under the effect of pressure

AbstractThe paper presents an investigation on crystalline, elastic and electronic structure in addition to the thermodynamic properties for a CeRu4P12 filled skutterudite device by using the full-potential linear muffin-tin orbital (FP-LMTO) method within the generalized gradient approximations (GGA) in the frame of density functional theory (DFT). For this purpose, the structural properties, such as the equilibrium lattice parameter, bulk modulus and pressure derivatives of the bulk modulus, were computed. By using the total energy variation as a function of strain we have determined the independent elastic constants and their pressure dependence. Additionally, the effect of pressure P and temperature T on the lattice parameters, bulk modulus, thermal expansion coefficient, Debye temperature and the heat capacity for CeRu4P12 compound were investigated taking into consideration the quasi-harmonic Debye model.

Electronic structure and x-ray magnetic circular dichroism of Mn-doped TiO2

The electronic structure of (Ti,Mn)O2 diluted magnetic semiconductors was investigated theoretically from first principles using the fully relativistic Dirac linear muffin-tin orbital band structure method. The electronic structure was obtained with the local spin-density approximation taking into account strong Coulomb correlations in the frame of the LSDA + U approximation. The x-ray absorption spectra and x-ray magnetic circular dichroism spectra at the Mn and Ti L2,3 and O K edges were investigated theoretically from first principles. The origin of the XMCD spectra in these compounds was examined. The calculated results are compared with available experimental data.

Elastic, Electronic, Optical and Thermal Properties of Na2Po: An Ab Initio Study

The structural, elastic, electronic, optical and thermodynamic properties of the sodium polonide Na2Po compound have been studied through the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) and tight-binding linear muffin-tin orbital (TB-LMTO) methods. The exchange–correlation potential was treated within the local density approximation for the TB-LMTO calculations and within the generalized gradient approximation for the FP-LAPW + lo calculations. In addition, Tran and Blaha-modified Becke–Johnson (TB-mBJ) potential and Engel–Vosko generalized gradient approximation were used for the electronic and optical properties. Ground state properties such as the equilibrium lattice constant, bulk modulus and its pressure derivative were calculated and compared with available data. The single-crystal and polycrystalline elastic constants of the considered compound were calculated via the total energy versus strain in the framework of the FP-LAPW + lo approach. The calculated electronic structure reveals that Na2Po is a direct band gap semiconductor. The frequency-dependent dielectric function, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for a wide energy range. The variations of the lattice constant, bulk modulus, heat capacity, volume expansion coefficient and Debye temperature with temperature and pressure were calculated successfully using the FP-LAPW + lo method in combination with the quasi-harmonic Debye model.

Structural, electronic and magnetic properties of FCC Ba2CoBO6 [B = Mo, W, Re, Os]: LSDA+U+SOC comparative investigation

First-principles calculations by the full potential linear muffin-tin orbital (FP-LMTO) method using local spin density approximation (LSDA), taking into account of both spin orbital coupling (SOC) and strong correlation (U) within the framework of spin-polarized density functional theory (DFT), were carried out for the structural, electronic and magnetic properties of a series of double perovskites Ba2CoBO6 (B=Mo, W, Re, Os). Structural optimizations of lattice constants show that all Ba2CoBO6 compounds crystallize in face-centered cubic (FCC) system with space group of (Fm3¯m), in good agreement with the experimental values. The relative stability of ferromagnetic (FM) and antiferromagnetic (AFM) orders is discussed. It is shown that it consistent with experimental results and AFM order is obtained when using LSDA and LSDA+U methods. The magnetic results show that the double perovskites Ba2CoBO6 are AFM through the anti-coupling Co2+ (3d7)↑–O2− (2p)–B6+ (4d/5d)n↓, where n=0, 1 or 2. DFT results show that the Ba2CoBO6 are half-metallic (HM) with energy-gaps in spin-up bands, but if B=Mo, it shows metallic nature in LSDA results, and it established that the U responsible for the AFM-HM in Ba2CoBO6.

Electronic and magnetic properties of interfaces of Ni with Ag/Cu/Au substrates using augmented space formalism

We model an interface of Ni as an alloy due to interdiffusion of atoms. Alloy composition is taken different at different layers. We observe significant effect of the interdiffusion on electronic and magnetic properties of each layer. These properties also depend on number of layers of Ni deposited on metal substrates. The study is density functional theory (DFT) based first principle calculation using augmented space formalism (ASF) coupled with recursion and tight binding linear muffin tin orbital (TB-LMTO) methods. The formalism is also extended to sharp interface when interdiffusion is negligible.

Superconductivity in Group III-V Semiconductor AlN Under High Pressure

The electronic properties of cubic zinc blende type group III-V semiconductor AlN under pressure is studied using full potential linear muffin-tin orbital (FP-LMTO) method. At normal pressure, AlN is an indirect bandgap semiconductor with band gap value 4.56 eV. When the pressure is increased, there is enhanced overlapping between the wave functions of the neighboring atoms. As a result the widths of the valence and empty conduction bands increase. These changes lead to the narrowing and indirect closing of the band gaps in AlN (metallization). On further increase of pressure, AlN becomes a superconductor and AlN comes under the class of electron-phonon-mediated high pressure superconductors. The superconducting transition temperatures (Tc) of AlN are obtained as a function of pressure for the CsCl structure. It is also confirmed that the metallization, structural phase transition and onset of superconductivity do not occur simultaneously in this compound. DOI: http://dx.doi.org/10.17807/orbital.v7i3.628

Effect of Na substitution on electronic and optical properties of CuInS2 chalcopyrite semiconductor

Electronic & optical properties of Na substituted CuNaIn2S4 chalcopyrite semiconductors are significantly modified due to Na substitution in the Cu deficient CuInS2 semiconductor. These properties are obtained form first principle calculation using density functional theory based tight binding Linear muffin tin orbital method. The presence of Na alters the structural distortion and enhances strengths of Cu d and S p hybridization in CuNaIn2S4. This effect reduces band gap, in agreement with experimental observations and modify other properties significantly. Calculations of optical matrix elements (OME) and joint density of states (JDOS) show that effects of Na substitution on optical properties come through p–d hybridization and structural distortion. OME contribution is prominent near band edge. Both systems show anisotropic optical properties.

Half-metallic properties and the robustness of Co2MnGe Heusler alloy under pressure: Ab-initio calculation

To investigate the structural, mechanical, electronic and magnetic properties of full Heusler Co2MnGe in L21 structure, we used first-principle calculations. We made use of all-electron full potential linearized muffin-tin orbital method (FP-LMTO) within the density functional theory. The generalized gradient approximation GGA allows describing the exchange correlation energy. The obtained lattice parameters, bulk modulus and its derivate are in good agreement with experimental and theoretical values. We have also calculated the elastic constants and their related parameters. GGA + U approach allows to process electronic properties. For our compound, the band structure and magnetic moments are treated at equilibrium lattice constant. At Fermi level, the material has a semi metallic behavior with 100% spin polarization ratio. Computed magnetic exchange constants are used to evaluate the Curie temperature from mean field-approximation (MFA). Finally the elastic constants, electronic structure and magnetic properties are investigated at high-pressure. We noticed that half-metal to metal transition was around 102 GPa. The increasing pressure does not affect-the total magnetic moment and the overall shape of the band structure which indicates the robustness of electronic structure of this system.

Electronic structure, magnetic ordering and X-ray magnetic circular dichroism in La_{1-x}Pr_{x}Co_{2}P_{2} phosphides

The electronic structure and magnetic ordering in La$_{1-x}$Pr$_x$Co$_2$P$_2$ ($x=$0, 0.25, and 1) phosphides have been studied theoretically using the fully relativistic spin-polarized Dirac linear muffin-tin orbital (LMTO) band-structure method. The X-ray absorption and X-ray magnetic circular dichroism spectra at the Co$L_{2,3}$ and Pr$M_{4,5}$ edges have been investigated theoretically within the framework of the LSDA+$U$ method. The core-hole effect in the final state as well as the effects of the electric quadrupole $E_2$ and magnetic dipole $M_1$ transitions have been investigated. Good agreement with experimental measurements has been found.

First-principles investigation of structural, mechanical, electronic, and bonding properties of NaZnSb

The structural, mechanical, electronic, and bonding properties and phase transition of NaZnSb are explored using the generalized gradient approximation based on ab initio plane-wave pseudopotential density functional theory.With the help of the quasi-harmonic Debye model, we probe the Gruneisen parameter, thermal expansivity, heat capacity, Debye temperature, and entropy of NaZnSb in the tetragonal phase. The results indicate that the lattice constants and the bulk modulus and its first pressure derivative agree well with the available theoretical and experimental data. NaZnSb in its ground state structure exhibits a distinct energy gap of about 0.41 eV, which increases with increasing pressure. Our conclusions are consistent with the theoretical predictions obtained by the ABINIT package, but are different from those obtained through the tight-binding linear muffin-tin orbital method. As a result, further experimental and theoretical researches need to be carried out. For the purpose of providing a comparative and complementary study for future research, we first investigate the thermodynamic properties of NaZnSb.