Full-potential Linear Muffin-tin Orbital Research Articles

First-principles study of structural, electronic and magnetic properties of double perovskite oxides Ba2CoMO6 (M=Mo and W)

Ba2CoMO6 (M=Mo and W) ordered double perovskite oxides have been investigated by using the first-principles of full potential linearized muffin-tin orbital (FP-LMTO) computational method. The structural, electronic and magnetic properties of Ba2CoMO6 were calculated using both the local spin density approximation (LSDA) and generalized gradient approximation (GGA) methods. The room temperature crystal structures of Ba2CoMO6 are face-centered cubic (space group Fm3¯m and tilt system a0a0a0) with lattice constants of (a=8.011Å) and (a=8.031Å) for (M=Mo) and (M=W), respectively. The crystals of Ba2CoMO6 contain alternating CoO6 and MO6 octahedra, almost fully ordered in the basal ab planes. It was shown that the obtained lattice constants agree well with the experimental data. The influence of M-cation on structural, electronic and magnetic properties of Ba2CoMO6 compounds is analyzed. The total and partial densities of states (DOSs) and partial and total spin magnetic moments are calculated, and the valence states of Co and M ions are examined. The magnetic and electronic properties and bond valence sums are consistent with the electronic configuration Co2+ (3d7)–M6+ (4d/5d)0 with Co2+ in high spin states.

A first principle study of phase stability, electronic structure and magnetic properties for Co2−xCrxMnAl Heusler alloys

The structural stabilities, electronic and magnetic properties of Co 2− x Cr x MnAl alloys with ( x =0,1 and 2) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the generalized gradient approximation (GGA) for the exchange correlation functional. The ground state properties including lattice parameter , bulk modulus for the two considered crystal structures Hg 2 CuTi-Type (X-Type) and Cu 2 MnAl-Type (L2 1 -Type) are calculated. The half-metallicity within ferromagnetic ground state starts to appear in CoCrMnAl and Cr2MnAl. In the objective for the proposition of the new HM-FM in the Full-Heusler alloys, our results classified CoCrMnAl as new HM-FM material with high spin polarization . • Based on DFT calculations, Co2-xCrxMnAl Heusler alloys have been investigated. • The magnetic phase stability was determined from the total energy calculations. • The LMTO calculations have classified CoCrMnAl as new HM-FM material with high spin polarization.

Electronic Band Structure and Metallization of Aluminium Nitride (AlN) under High Pressure

One basic problem in solid state physics, material chemistry, geosciences and even in planetology, is the precise electronic properties of the materials present in objects. The uniqueness of aluminium nitride (AlN) and its special role in human society is closely related to its structural stability at extreme pressures. In this paper, the results of a full potential linear muffin-tin orbital (FP-LMTO) study on the electronic properties of cubic zinc blende type group III-V semiconductor aluminium nitride (AlN) under pressure are presented. The equilibrium lattice constant, bulk modulus, pressure derivative of bulk modulus and the phase transition pressure from ZnS to NaCl is predicted from the total energy calculations. The ground state properties and band gap values are compared with the experimental results. At normal pressure AlN is indirect bandgap semiconductor with bandgap value 4.56eV. When the pressure is increased there is enhanced overlapping between the wave functions of the neighbouring atoms. As a result the widths of the valence and empty conduction bands increase. These changes lead to the narrowing and indirect closing of band gaps in AlN (metallization). In AlN, the metallization (at V/Vo=0.756 and PM = 1 Mbar) occurs through indirect closing of the band gap between valence band maximum at  point and conduction band minimum at X point. It is also confirmed that the metallization and structural phase transition do not occur simultaneously in this compound.

Full Potential Calculation of the Band-Gaps in GaP/GaN Superlattices

The present paper deals with the electronic properties of GaP and GaN zinc-blende/zincblende superlattices using the plane wave version of the full potential linear muffin-tin orbital (FPLMTO) method, which allows an accurate treatment of the interstitial regions. It is found that bowing, which is known to occur for ternary GaPN dilute nitrides, is absent from GaP/GaN 〞dilute nitride〞 superlattices with N concentrations greater than 7%, but it can be obtained in these same superlattices for high nitride concentrations.

First-principles study of the electronic and structural properties of (CdTe)n/(ZnTe)n superlattices

We present the results of a first-principles study of the electronic and structural properties of binary CdTe and ZnTe compounds and their (CdTe)n/(ZnTe)n superlattices (SLs). The computational method is based on the full-potential linear muffin tin orbitals method (FP-LMTO) augmented by a plane-wave basis (PLW). The exchange and correlation energy is described in the local density approximation (LDA) using the Perdew–Wang parameterization including a generalized gradient approximation (GGA). The calculated structural properties of CdTe and ZnTe compounds are in good agreement with available experimental and theoretical data. We have also carried out band-structure calculations for the binary CdTe and ZnTe compounds and their (CdTe)n/(ZnTe)n superlattices (SLs). From the results of the electronic properties, we find that the parent material CdTe and ZnTe and their superlattices have a direct band gaps. The fundamental band gap decreases with increasing the number of monolayer n.

First-principles calculations to investigate structural, electronic and optical properties of (BeTe)n/(CdS)n superlattices

Structural, electronic and optical properties of binary BeTe and CdS compounds and their (BeTe)n/(CdS)n superlattices (SLs) are investigated using the first-principles full potential linear muffin-tin orbitals method (FP-LMTO). The exchange–correlation potential is treated with the local density approximation of Perdew and Wang (LDA-PW). The ground-state properties are determined for the bulk materials (BeTe, CdS, and (BeTe)n/(CdS)n) in cubic phase. The calculated structural properties of BeTe and CdS compounds are in good agreement with available experimental and theoretical data. It is found that BeTe exhibit an indirect fundamental band gap and CdS and their superlattices (SLs) exhibit a direct fundamental band gap, which might make (BeTe)n/(CdS)n superlattices (SLs) materials promising and useful for optoelectronic applications. The fundamental band gap decreases with increasing the number of monolayer n.

Structural, elastic, electronic and thermodynamic properties of uranium filled skutterudites UFe4P12: First principle method

We present a theoretical study of structural, elastic, thermodynamic, and electronic properties of the uranium filled skutterudite UFe4P12. We use the full-potential linear muffin–tin orbital (FP-LMTO) method in which the local density approximation (LDA) is used for the exchange-correlation (XC) potential. The lattice parameter at equilibrium, the bulk modulus, its pressure derivative, the elastic constants and the band structure energy of the filled skutterudite UFe4P12 are calculated and systematically compared to available theoretical and experimental data. Herein, we use the total energy variation as function of strain technique to determine independent elastic constants and their pressure dependence. Furthermore, using quasi-harmonic Debye model with phonon effects, the effect of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature and the heat capacity of UFe4P12 are investigated for the first time. Band structure of UFe4P12 indicates a tendency of forming a pseudo-gap that appears above the Fermi level at Γ point. This is a unique characteristic of skutterudite, especially when a single phosphorous p-band crosses the Fermi level. The crossing band is, indeed, pushed down by the repulsion of U f-resonance states.

Electronic, magnetic and optical properties of cubic double perovskites Ba2CrMoO6 and Ba2CrWO6 with (d3–d1) system

The electronic, magnetic and optical properties of cubic double perovskites Ba2CrMoO6 and Ba2CrWO6 have been studied by using full potential linear muffin-tin orbital (FP-LMTO) computational method within the local spin density approximation (LSDA) as well as taking into account the on-site Coulomb repulsive interaction in (LSDA+U) approach. The band structure results reveal a similar half-metallic (HM) ferrimagnetic (FiM) ground state in two compounds with total spin magnetic moments closed to the theoretical value (m=2.0μB/f.u.). The LSDA and LSDA+U calculations predict an energy-gap in the spin-up bands, while a finite density of states for the spin-down bands in Ba2CrMoO6 and Ba2CrWO6. HM–FiM organizes from the ddpπ super-exchange interaction (3d-t2g3↑–O 2pπ–4d/5d-t2g1↓) in accordance with the Pauli Exclusion Principle and Goodenough–Kanamori rules. The real and imaginary parts of dielectric functions were calculated and the inter-band contributions to the optical properties have been analyzed. The HM–FiM nature with (SP=−1.0) implies a promising applications of Ba2CrMoO6 and Ba2CrWO6 materials in magnetoelectronic and spin-electronics technology.

High-pressure study of binary thorium compounds from first principles theory and comparisons with experiment.

The high-pressure structural behaviour of a series of binary thorium compounds ThX (X = C, N, P, As, Sb, Bi, S, Se, Te) is studied using the all-electron full potential linear muffin-tin orbital (FP-LMTO) method within the generalized gradient approximation (GGA) for the exchange and correlation potential. The calculated equlibrium lattice parameters and bulk moduli, as well as the equations of state agree well with experimental results. New experiments are reported for ThBi and ThN. Calculations are performed for the ThX compounds in the NaCl- and CsCl-type crystal structures, and structural phase transitions from NaCl to CsCl are found in ThP, ThAs, ThSb and ThSe at pressures of 26.1, 22.1, 8.1 and 23.2 GPa, respectively, in excellent agreement with experimental results. ThC, ThN and ThS are found to be stable in the NaCl structure, and ThBi and ThTe in the CsCl structure, for pressures below 50 GPa. The electronic structures of the ThX compounds are studied using the quasiparticle self-consistent GW method (G: Green function, W: dynamically screened interaction).

Band Gap Engineering ofCd1-xBexSeAlloys

The structural and electronic properties of the ternaryCd1-xBexSealloys have been calculated using the full-potential linear muffin-tin-orbital (FP-LMTO) method based on density functional theory within local density approximation (LDA). The calculated equilibrium lattice constants and bulk moduli are compared with previous results. The concentration dependence of the electronic band structure and the direct and indirect band gaps are investigated. Moreover, the refractive index and the optical dielectric constant forCd1-xBexSeare studied. The thermodynamic stability of the alloys of interest is investigated by means of the miscibility. This is the first quantitative theoretical prediction to investigate the effective masses, optical and thermodynamic properties forCd1-xBexSealloy, and still awaits experimental.

La-doping effects on structural, electronic and magnetic properties of Ba2–xLaxCrMO6 (M = Mo, Nb): LMTO-PLW + (LSDA + U) study

The La doped Cr-based double perovskite Ba2–xLaxCrMO6, where M = Mo, Nb and (x = 0, 1 and 2), have been studied by employing full potential linear muffin-tin orbital (FP-LMTO) within the atomic plane wave (PLW) method. Effects of La-doping on structural, electronic and magnetic properties of Ba2–xLaxCrMO6 have been studied within the correlated local-spin-density approximation (LSDA + U) method. The crystal structure of Ba2–xLaxCrMO6 decreases from cubic Fm-3m (x = 0, 1) to tetragonal I4/m (x = 2). The La-doping favors the reduction of Cr3+ and M5+ which plays a vital role in determining the electronic and magnetic properties. The results show that all Ba2–xLaxCrMO6 compounds are half-metallic-ferrimagnetic, except Ba2CrNbO6 (x = 0), which is a ferromagnetic-insulator. With increasing x content the magnetic moment of Mo and Nb distinctly increases and the doped electrons occupy chiefly the 4d↓ orbitals.

First-principles Study of High-pressure Phases of AlN

Abstract We report study of high-pressure phases of AlN compound, using a recent version of the full potential linear muffin-tin orbitals method (FPLMTO) which enables an accurate treatment of the interstitial regions. The Exchange-correlation has been accounted for within LDA using the exchange-correlation potential calculated by Perdew et al. Calculations are given for lattice parameters, bulk modulus and its first derivatives in the wurtzite, zinc-blende, rock-salt, CsCl, NiAs, βSn, the Cinnabar and the hexagonal structures. The results of these calculations are compared with the available theoretical and experimental data.

Theoretical Investigation of GaN

Abstract Using the Full Potential Linear Muffin Tin Orbitals (FPLMTO) method, the structural properties of GaN were studied. Different crystal structures were considered: NaCl, CsCl, wurtzite, zincblende, β-tin, Cinnabar and NiAs structures. The wurtzite is the calculated ground state structure. Results are given for lattice parameters, bulk modulus and its first derivative in the different cases. The phase transitions for GaN were also investigated. The results are compared with the available theoretical and experimental data. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of the volume, the bulk modulus, the variation of the thermal expansion α, as well as the heat capacity Cv were successfully obtained in the whole range from 0 to 30 GPa and temperature range from 0 to 1000 K.

Band Structure, Metallization and Superconducting Transition Of Group III-V Semiconductors AlP And AlAs Under High Pressure

The results of a full potential linear muffin-tin orbital (FP-LMTO) study on the electronic properties of cubic zinc blende type group III-V semiconductors AlP and AlAs under pressure are presented. The equilibrium lattice constant, bulk modulus, pressure derivative of bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl and NaCl to CsCl are predicted from the total energy calculations. The ground state properties and band gap values are compared with the experimental results. At normal pressure AlP and AlAs are indirect bandgap semiconductors. When the pressure is increased there is enhanced overlapping between the wave functions of the neighbouring atoms. As a result the widths of the valence and empty conduction bands increase. These changes lead to the narrowing and indirect closing of band gaps in AlP and AlAs (metallization). On further increase of pressure, AlP and AlAs become superconductors, and these materials come under the class of electron-phonon-mediated high pressure superconductors. The superconducting transition temperatures (Tc) of AlP and AlAs are obtained as a function of pressure for CsCl structure. It is also confirmed that the metallization, structural phase transition and onset of superconductivity do not occur simultaneously in these compounds.

The influence of the M (3d) replacement on structural, electronic and magnetic properties of Nb-based double perovskite Ba2MNbO6 (M = Sc, Ti, V and Cr): From FP-LMTO studies

Employing the self-consistent full-potential linear muffin-tin orbital (FP-LMTO) computational method, systematic studies have been performed on the influence of M (3d) replacement on structural, electronic and magnetic properties of novel Nb-based barium double perovskite Ba2MNbO6 (M (3d)=Sc, Ti, V and Cr). The crystal structure calculations show that the Ba2MNbO6 structures are in face-centered cubic with a space group (Fm-3m). The band structure calculations have been performed using the correlated local spin density approximation (LSDA+U). The results showed that Ba2TiNbO6 and Ba2VNbO6 are half-metallic ferromagnetic materials in ground states, having energy-gaps in the spin-down bands and finite densities of states in the spin-up bands. While an insulating and ferromagnetic behaviors were obtained in Ba2ScNbO6 and Ba2CrNbO6. It is found that the M3+ (3d-t2gn) ions (0⩽n⩽3) have major influence, while the nonmagnetic Nb5+ (4d-t2g0) ions have minor effect, on electronic conducting and magnetic moment in Ba2MNbO6.

Structural, Electronic, and Optical Properties of (LaN)n/(ScN)n and (LaN)n/(YN)n Superlattices

The structural, electronic, and the optical properties of (LaN)n/(ScN)n and (LaN)n/(YN)n superlattices are investigated using the recent version of the first principles full potential linear muffin-tin orbitals method (FP-LMTO). The resemblances between LaN, ScN, and YN and their small lattice mismatch led us to perform investigations on rocksalt/rocksalt (LaN)n/(ScN)n, and (LaN)n/(YN)n for n = 1, 2, and 3 monolayers. Our calculations performed for the band structure and density of states show indirect band gap superlattices for n = 1, 2, and 3. Details of the electronic structure and optical properties of the superlattices are discussed.

First-principles study of structural stabilities, elastic and electronic properties of transition metal monocarbides (TMCs) and mononitrides (TMNs)

The structural stabilities, elastic and electronic properties of 5d transition metal mononitrides (TMNs) XN with (X = Ir, Os, Re, W and Ta) and 5d transition metal monocarbides (TMCs) XC with (X = Ir, Os, Re and Ta) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the local density approximation (LDA) for the exchange correlation functional. The ground state quantities such as the lattice parameter, bulks modulus and its pressure derivatives for the six considered crystal structures, Rock-salt (B1), CsCl (B2), zinc-blend (B3), Wurtzite (B4), NiAs (B81) and the tungsten carbides (Bh) are calculated. The elastic constants of TMNs and TMCs compounds in its different stable phases are determined by using the total energy variation with strain technique. The elastic modulus for polycrystalline materials, shear modulus (G), Young's modulus (E), and Poisson's ratio (ν) are calculated. The Debye temperature (θD) and sound velocities (vm) were also derived from the obtained elastic modulus. The analysis of the hardness of the herein studied compounds classifies OsN – (B4 et B81), ReN – (B81), WN – (B81) and OsC – (B81) as superhard materials. Our results for the band structure and densities of states (DOS), show that TMNs and TMCs compounds in theirs energetically and mechanically stable phase has metallic characteristic with strong covalent nature Metal–Nonmetal elements.

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.

FP-LMTO method to calculate the structural, thermodynamic and optoelectronic properties of SixGe1−xC alloys

The structural and electronic properties of the ternary SixGe1−xC alloys have been calculated using the full-potential linear muffin-tin-orbital (FP-LMTO) method based on density functional theory within both local density approximation (LDA) and generalised gradient approximation (GGA). The calculated equilibrium lattice constants and bulk moduli are compared with previous results. The concentration dependence of the electronic band structure and the direct and indirect band gaps are investigated. Using the approach of Zunger and co-workers, the microscopic origins of the band gap bowing are investigated also. Moreover, the refractive index and the optical dielectric constant for SixGe1−xC are studied. The thermodynamic stability of the alloys of interest is investigated by means of the miscibility. This is the first quantitative theoretical prediction to investigate the effective masses, optical and thermodynamic properties for SixGe1−xC alloy, and still awaits experimental confirmations.

FP-LMTO investigation of the structural, electronic and agneticproperties of Heusler compounds Ru2CrZ (Ge, Sn, Si)

The electronic structure of the antiferomagnetic full Heusler alloys Ru2CrZ (Ge, Sn, Si) have been studied by first principal calculations using Full-Potential linearized Muffin Tin Orbital (FP-LMTO) method based on the generalized Gradient Approximation (GGA). It was shown that obtained equilibrium lattice parameters agree well with available experimental data. The influence of Z-elements on the electronic structure and magnetic properties of these compounds is analysed.