Co doping effects on structural, electronic and magnetic properties in Mn2VGa

The electronic structure and magnetic properties of Co-doped Heusler alloys (Mn_1−xCo_x)₂ VGa (x=0.0, 0.25, 0.5, 0.75, 1.0) have been studied by first-principles calculations. The results show that the lattice constants decrease with increasing Co content except x=1.0. The spin polarization for x=0.5 is only 34%, much lower than the other concentrations. The compounds of x=0.0, 0.25 show nearly half-metallicity because the Fermi level slightly touches the valence bands. And the compounds of x=0.75, 1.0 exhibit the half-metallic character with 100% spin polarization. It is found the local moments of Mn(Co) basically show a linear increasing trend while the moments of V show a linear decreasing trend with increasing doping concentration. However, the local moments for x=0.5 quite depart from the linear trend. The majority-spin component at the Fermi level increases while the minority-spin component at the Fermi level decreases with the substitution of Co atoms for Mn atoms when x≤0.75. For x≥0.75, the majority-spin component remains more or less the same and the gap in the minority DOS increases with Co doping. The majority spin states are shifted to valence bands and the majority spin states around E_F increase due to a leakage of charge from the unoccupied spin-up states to the occupied majority states with increasing Co content.     

First-principles study on the electronic structure, magnetic properties and phase stability of alloyed cementite with Cr or Mn

Using the first-principles technique, the electronic structures, magnetic properties and phase stability of alloyed cementite with Cr or Mn were investigated. The calculations show that the chemical and mechanical stability of alloyed cementite can be strengthened by the use of Cr/Mn-doped method. The Magnetic Moments (Ms) of Mn₁Fe₂C, Mn₂Fe₁C, Cr₁Fe₂C and Cr₂Fe₁C are 5.274, 0.941, 1.864 and 0.736 μ_B/f.u, respectively. The Ms of Cr in Fe₂CrC (−1.374 μ_B) and Cr₂FeC (−0.032 μ_B) are different due to replacing different sites Fe atoms. The magnetic behaviors of Mn are different from Cr in alloyed cementite. The Ms of Mn in Fe₂MnC and Mn₂FeC are 2.300 μ_B and −0.147 μ_B, respectively.     

Ab initio study of the structural,electronic, elastic and magnetic properties of Cu2GdIn,Ag2GdIn and Au2GdIn

We preformed first-principle calculations for the structural, electronic, elastic and magnetic properties of Cu₂GdIn, Ag₂GdIn and Au₂GdIn using the full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation by Wu and Cohen (GGA-WC), GGA+U, the local spin density approximation (LSDA) and LSDA+U. The lattice parameters, the bulk modulus and its pressure derivative and the elastic constants were determined. Also, we present the band structures and the densities of states. The electronic structures of the ferromagnetic configuration for Heusler compounds (X₂GdIn) have a metallic character. The magnetic moments were mostly contributed by the rare-earth Gd 4f ion.     

First-principles investigation of structural,elastic, electronic and magnetic properties of Be0.75Co0.25Y (YS,Se and Te) compounds

We have theoretically investigated the structural, elastic, electronic and magnetic properties of Be_0.75Co_0.25Y (YS, Se and Te) alloys, in their zinc-blend phase. This study is carried out by using the full-potential augmented plane wave plus local orbitals method within the density functional theory. Foe computing the exchange-correlation potential, the Wu and Cohen generalized gradient approximation is employed to calculate structural and elastic properties whereas the modified Becke and Johnson potential local density approximation is utilized to examine electronic and magnetic properties. By minimizing the total energy in paramagnetic (PM) and ferromagnetic (FM) phases, it is found the studied compounds are stable in FM structure. The mechanical behavior of the studied compounds is reported with the calculation of shear modulus, Young's modulus, and Poisson's ratio provides. Such mechanical aspects might be useful for the experimentalists to study the mechanical properties upon alloying BeY compounds with Co. We also compute electronic structures, density of states (total and partial), pd-exchange splitting and magnetic moments. Moreover, bond nature is studied by estimating the spin polarized charge densities of Be_0.75Co_0.25Y (YS, Se and Te).     

Structural,electronic, magnetic and vibrational properties of half-Heusler NaZrZ (Z = P,As, Sb) compounds

The structural, electronic, magnetic and vibrational properties of NaZrP, NaZrAs and NaZrSb half-Heusler alloys have been investigated on the basis of density functional theory and generalized gradient approximation. There are three types of structures for these compounds where type a is the most stable one. It is found that all of these materials are half-metallic ferromagnets with a magnetic moment of $2{\mu }_{\mathrm{B}}$. The half-metallic gaps are estimated to be 0.16, 0.35 and 0.55 eV for Z = P, As and Sb, respectively. The hybridization between s and $t_{2g}$ orbitals of Zr with s and p orbitals of Z leads to half-metallic ferromagnetism in these compounds. The effect of strain on the half-metallic property is also investigated, and we notice that the half-metallicity is conserved up to the lattice compressions of 54.43%, 48.29% and 47.55% for NaZrP, NaZrAs and NaZrSb, respectively. The dynamical stability of these compounds is confirmed using dispersion curves. The Curie temperatures are also estimated to be 501.29 K, 855.49 K and 1348.88 K for NaZrP, NaZrAs and NaZrSb, respectively. Therefore, it seems that NaZrZ (Z = P, As, Sb) could be suitable materials for spin-injector applications.     

First-principle study of phase stability,electronic structure and thermodynamic properties of cadmium sulfide under high pressure

By employing first principle and a quasi-harmonic Debye model, we study the phase stability, phase transition, electronic structure and thermodynamic properties of cadmium sulfide (CdS). The results indicate that CdS is a typical ionic crystal and that the zinc-blende phase in CdS is thermodynamically unstable. Moreover, the heat capacity of the wurtzite and rocksalt phases of CdS decreases with pressure and increases with temperature, obeying the rule of the Debye T³ law at low temperature and the Dulong–Petit limit at high temperature.     

First-principle study of the electronic and optical properties of BInGaAs quaternary alloy lattice-matched to GaAs

The first-principle calculations based on density functional theory have been used to study the electronic and optical properties of zinc-blende BInGaAs quaternary alloy lattice-matched to GaAs. The calculated results show the band gap of BInGaAs alloy are direct and the band gap will reduce with the increment of boron and indium composition. The electronic structures of BInGaAs alloy are analyzed via the calculation of density of states. The variation of optical properties including dielectric function, absorption coefficient, reflectivity, refractive index and energy loss function of the alloy were also investigated in detail.     

Structural,electronic and magnetic properties of the double perovskite Pb2FeReO6

The structural, electronic and magnetic properties of the double perovskite Pb₂FeReO₆ have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive and exchange coupling interactions (GGA+U). The optimized crystal structure of the Pb₂FeReO₆ is a body-centered tetragonal (BCT) with a space group of I4/m and the lattice constants of a=b=5.59 Å and c=7.93 Å, consistent with the experimental results. The two axial transition metal and oxygen (TM–O) distances are slightly larger than the four equatorial TM–O distances and shows the existence of the Jahn–Teller structural distortion in FeO₆ and ReO₆ octahedra. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.929 and −0.831μ_B respectively and thus antiferromagnetic (AFM) coupling via oxygen between them. The half-metallic (HM) ferromagnetic (FM) nature implies a potential application of this new compound in magnetoelectronic and spintronics devices.     

First-principles study of structural stability, electronic and elastic properties of ZrC compounds

We theoretically study the possible pressure-induced structural phase transition, electronic and elastic properties of ZrC by using first-principles calculations based on density functional theory (DFT), in the presence and absence of spin-orbit coupling (SOC). The calculations indicate that there exists a phase transition from the NaCl-type (B1) structure to CsCl-type (B2) structure at the transition pressure of 313.2 GPa (without SOC) and 303.5 GPa (with SOC). The detailed structural changes during the phase transition were analyzed. The band structure shows that B1-ZrC is metallic. A pseudogap appears around the Fermi level of the total density of states (DOS) of the B1 phase of ZrC, which may contribute to its structural stability.     

First-principle calculations of structural,electronic and magnetic investigations of Mn2RuGe1-xSnx quaternary Heusler alloys

First-principles calculations were used to calculate the structural, electronic and half-metallic ferromagnetism of Mn₂RuGe_1-xSn_x (x?=?0, 0.25, 0.50, 0.75, 1) Heusler alloys. The Hg₂CuTi-type structure is found to be energetic more than Cu₂MnAl-type structure for both Mn₂RuGe and Mn₂RuSn compounds. The calculated lattice constants for Mn₂RuGe and Mn₂RuSn are 5.91?Å and 6.17?Å, respectively. The electronic band structures and density of states of Mn₂RuGe show a half metallic character with total magnetic moments, 2 μ_B per formula unit that are in good agreement with Slater-Pauling rule with indirect band gap, 0.31?eV along the direction Γ –X. It is observed that the total magnetic moment per cell increases as Sn concentration increases in the Heusler alloys.     

First-principles study on the structural and electronic properties of ultrathin ZnO nanofilms

Using first-principles density-functional calculations, we have studied the structural and electronic properties of ultrathin ZnO {0001} nanofilms. The structural parameters, the charge densities, band structures and density of states have been investigated. The results show that there are remarkable charge transfers from Zn to O atoms in the ZnO nanofilms. All the ZnO nanofilms exhibit direct wide band gaps compared with bulk counterpart, and the gap decreases with increased thickness of the nanofilms. The decreased band gap is associated with the weaker ionic bonding within layers and the less localization of electrons in thicker films. A staircase-like density of states occurs at the bottom of conduction band, indicating the two-dimensional quantum effects in ZnO nanofilms.     

First-principles study of the structural, elastic, electronic and optical properties of the monoclinic BiScO3

The structural, elastic, electronic and optical properties of the monoclinic BiScO₃ are investigated in the framework of the density functional theory. The calculated structural parameters are in agreement with the experimental values. Moreover, the structural stability of BiScO₃ system has been confirmed by the calculated elastic constants. The band structure, density of states, charge transfers and bond populations are also given. The results indicate that BiScO₃ has a direct band gap of 3.36 eV between the occupied O 2p states and unoccupied Bi 6p states, and its bonding behavior is a combination of covalent and ionic nature. Finally, the absorption spectrum, refractive index, extinction coefficient, reflectivity, energy-loss function and dielectric function of the monoclinic BiScO₃ are calculated. In addition, the variation of the static dielectric constants ε₁(0) as a function of pressure for BiScO₃ is also discussed.     

Orbital-decomposed electronic and magnetic properties of the double perovskite Sr2FeReO6

The detailed orbital-decomposed electronic structures and magnetic properties of the double perovskite Sr₂FeReO₆ have been studied using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). Both occupied and unoccupied s and three p states of Fe³⁺ ion are located far away from the Fermi level, while all up-spin states and most down-spin states are completely filled for the s and three p states of Re⁵⁺ ion. The octahedral crystal field of the oxygen atoms around transition-metal (TM) sites splits the five-fold degenerate d states of the free TM atoms into triply degenerate t_2g states with smaller bonding-antibonding splitting and doubly degenerate e_g states with larger bonding-antibonding splitting. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.70 and −0.86μ_B, respectively and thus antiferromagnetic coupling via oxygen between them. There are no direct interactions between two nearest Fe-Fe or Re-Re pairs, whereas along each Fe-O-Re-O-Fe or Re-O-Fe-O-Re chains, the hybridizations between Fe 3d and 4s, O 2s and 2p, as well as Re 5p, 5d and 6s orbitals are fairly significant.     

First-principle study of structural and electronic properties of ternary layered Ta2AlC

The structural and electronic properties of ternary layered Ta₂AlC ceramics have been studied using the first-principle method based on the density-functional theory. We have obtained the equilibrium lattice parameters and the equilibrium atomic positions in the unit cell. The equilibrium lattice parameters are computed to be a=b=3.15 Å and c=13.95 Å. The internal coordinates of Ta are determined to be (1/3, 2/3, 0.092). The band structure and density of states reveal that Ta₂AlC is an electronic conductor. The charge density distribution shows that the Ta and C atoms form a strong Ta-C-Ta covalently bonded chain.     

First principles study of structural,magnetic and electronic properties of CrAs

Abstract

We report ab initio density functional calculations of the structural and magnetic properties, and the electronic structure of CrAs. To simulate the observed pressure-driven experimental results, we perform our analysis for different volumes of the unit cell, showing that the structural, magnetic and electronic properties strongly depend on the size of the cell. We find that the calculated quantities are in good agreement with the experimental data, and we review our results in terms of the observed superconductivity.     

First principles study on the structural, electronic, and elastic properties of Na-As systems

We have performed the first principles calculation by using the plane-wave pseudopotential approach with the generalized gradient approximation for investigating the structural, electronic, and elastic properties Na-As systems (NaAs in NaP, LiAs and AuCu-type structures, NaAs₂ in MgCu₂-type structure, Na₃As in Na₃As, Cu₃P and Li₃Bi-type structures, and Na₅As₄ in A₅B₄-type structure). The lattice parameters, cohesive energy, formation energy, bulk modulus, and the first derivative of bulk modulus (to fit to Murnaghan’s equation of state) of the related structures are calculated. The second-order elastic constants and the other related quantities such as Young’s modulus, shear modulus, Poisson’s ratio, sound velocities, and Debye temperature are also estimated.     

First-principles study of the structural, electronic, and magnetic properties of InCCo3 and InNCo3

Spin-polarized calculations were performed to investigate the structural, elastic, electronic, and magnetic properties of InCCo₃ and InNCo₃. The deviation of our calculated lattice parameters and equilibrium volume from experimental results is less than 0.8% and 2.5%, respectively. The obtained values of elasticity moduli C_ij, bulk modulus B, and shear modulus G are discussed. From the calculated band structure and the total and partial densities of states, we have concluded that these compounds are electrical conductors; moreover, they are bonded by a mixture of covalent, ionic, and metallic bonds. Our calculations show that InCCo₃ has nonmagnetic properties, while InNCo₃ could have a magnetic behaviour, with an average magnetic moment about 0.54 μ_B/atom, which is mostly derived from d electrons of the cobalt atoms in the energy range from −5 eV up to the Fermi level.     

The investigation of structural,electronic, elastic and thermodynamic properties of Gd1−xYxAuPb alloys: A first principle study

First principle calculations have been employed to investigate the effects of Y concentration, pressure and temperature on various properties of ${\mathrm{Gd}}_{1?x}{\mathrm{Y}}_x\mathrm{AuPb}$ ($x=0,0.25,0.5,0.75,1$) alloys using density functional theory (DFT). The full potential linearized augmented plane wave (FP-LAPW) method within a framework of the generalized gradient approximation (GGA) is used to perform the calculated results of this paper. Phase stability of ${\mathrm{Gd}}_{1?x}{\mathrm{Y}}_x\mathrm{AuPb}$ alloys is studied using the total energy versus unit cell volume calculations. The equilibrium lattice parameters of these alloys are in good agreement with the available experimental results. The mechanical stability of ${\mathrm{Gd}}_{1?x}{\mathrm{Y}}_x\mathrm{AuPb}$ alloys is proved using elastic constants calculations. Also, the influence of Y concentration on elastic properties of ${\mathrm{Gd}}_{1?x}{\mathrm{Y}}_x\mathrm{AuPb}$ alloys such as Young's modulus, shear modulus, Poisson's ratio and anisotropy factor are investigated and analyzed. By considering both Pugh's ratio and Poisson's ratio, the ductility and brittleness of these alloys are studied. In addition, the total density of states and orbital's hybridizations of different atoms are investigated and discussed. Moreover, the effect of pressure and temperature on some important thermodynamic properties is investigated.     

Calculated structural, electronic and optical properties of Ga-based semiconductors under pressure

The structural, electronic and optical properties of GaP, GaAs and GaSb at ambient and under hydrostatic pressure have been calculated using the full potential linear augmented plane wave (FP-LAPW) method. The calculated lattice constant, bulk modulus and its pressure derivative are compared with available experimental data. The first and second order pressure coefficients for the (Γ-Γ) energy gaps and hydrostatic deformation potential shows agreement with measurement. The linear pressure coefficients of the transition (Γ-Γ) increases significantly as anion atomic number increases (GaP→GaAs→GaSb). The magnitude of linear pressure coefficient of the transition (Γ-X) are small and usually negative. The variation of linear pressure coefficient of the transition (Γ-L) are relatively small and follow similar trend as (Γ-Γ). Overall the calculated linear and nonlinear pressure coefficients show good agreement with the experimental data. The obtained dielectric function, refractive index, extinction coefficient and reflectivity are compared with measured data and show qualitatively good agreement.