Full-potential Linear Muffin-tin Orbital Research Articles

First-principles study of structural, electronic and magnetic properties of diluted magnetic semiconductor and superlattices based‏ on Cr-doped ZnS and ZnSe compounds in wurtzite-type crystal

We performed first-principle calculations to investigate the structural, electronic, and magnetic properties of ZnS and ZnSe binary compounds, Zn0.5Cr0.5S and Zn0.5Cr0.5Se DMS alloys and (ZnS)2/Zn0.5Cr0.5Se and (ZnSe)2/Zn0.5Cr0.5S superlattices in the wurtzite structure using the full potential linear muffin–tin orbital (FP-LMTO) method. Features such as lattice constant, modulus of compressibility and its first derivative, spin-polarized band structures, total and local or partial electronic densities of states and magnetic properties were calculated. The electronic structure shows that Zn0.5Cr0.5S and Zn0.5Cr0.5Se DMS alloys and (ZnS)2/Zn0.5Cr0.5Se and (ZnSe)2/Zn0.5Cr0.5S superlattices are half-metallic ferromagnetic with 100% complete spin polarization. The total magnetic moments calculated show the same integer value of 4 µB, which confirms the ferromagnetic half-metallic behavior of these compounds. We found that the ferromagnetic state is stabilized by the p-d exchange associated with the double-exchange mechanism. Zn0.5Cr0.5S and Zn0.5Cr0.5Se DMS alloys and (ZnS)2/Zn0.5Cr0.5Se and (ZnSe)2/Zn0.5Cr0.5S superlattices are shown to be promising new candidates for applications in the fields of spintronics.

Topologically nontrivial phase in Na2CuX (X= As, Sb, Sn and Bi) full Heusler compounds: Insights from DFT-based computer simulation

The inspection of materials supporting topological excitations is one of the prospective areas of condensed matter physics. This paper is devoted to studying the possibility of the existence of topological phases in Na2CuX (X= As, Sb, Sn and Bi) full Heusler compounds using the FP-LMTO (Full-Potential Linear Muffin-Tin Orbital) method with and without spin-orbit coupling (SOC). The study of structural properties has found that these materials are energetically stable in the Hg2CuTi type structure. Also, formation energy calculations have shown that these materials are convenient to manufacture. Otherwise, band structure calculations show that these materials exhibit the behavior of non-trivial topological materials with a semi-metallic nature. The obtained results in this study, generally, showed that SOC is not a primary cause of the band inversion mechanism.

Atomistic study of stability and new phase transitions of zinc selenide using FP-LMTO-PLW method

By full potential linear muffin-tin orbitals (FP-LMTO-PLW) method, we have studied the phase transitions of ZnSe under high pressures. The local density approximation (LDA) was used for the exchange and correlation energy. The most important result is the prediction of the possibility of four phase transitions from the cubic zincblende (ZnS-B3) to the B81 (NiAs) structure at 8.00 GPa, the second from B3 to the B32 (NaTi) and Bh (WC) structures at above 45 GPa for each one of them, and from B3 to B2 (CsCl) phase at around 31GPa. The first one (ZnS–NiAs) occurring at a lower pressure than the well knownZnS to NaCl transition (found here to be 11.5 GPa).

Mg substitution in zinc selenide: Enhanced optoelectronic and thermoelectric performance

AbstractIn this research, we applied a full‐potential linearized muffin‐tin orbital (FP‐LMTO) method to investigate the optoelectronic properties such as electronic structures and optical properties in the first phase, and then we try to improve the thermoelectric performance through the substitution by an element alkaline earth metal (Mg). The analysis of band structure and optical properties indicate a semiconductors character with wide directly band gap along alkaline earth metal element (Mg) substitution. The present comprehensive analyses of electronic and optical properties of these alloys predict that they could be useful for optoelectronic devices. Thermal parameters such as thermal conductivity and power factor show good improvement for very small substitutions; this tells me that our material has a ZT close to promising alloys in thermoelectric applications. This result encourages going deep in order to obtain good thermoelectric performance at high temperature which requires adjusting the concentration of carriers, thermal conductance and the amount of Mg. At the end, Mg doped ZnSe is a favorable material for both optoelectronic and thermoelectric application.

Electronic structure of short-period ZnSe/ZnTe superlattices based on DFT calculations

In the present study we discuss the effect of variation in the number of monolayers n on the electronic and optical properties of superlattices (SLs) (ZnSe)n/(ZnTe)n. The total energies were calculated by the full-potential linear muffin-tin orbital (FP-LMTO) method, and the exchange-correlation energy was applied in the local density approximation (LDA). First, the calculations show a decrease in the derivative of bulk modulus and electronic bandgap with an increase in the number of monolayers n. Second, the radiation energies up to 15 eV, the dielectric function ε(ω), the refractive index n(ω), and the reflectivity R(ω) are studied. These calculations may be beneficial to understand the properties of short-period superlattices (ZnSe)n/(ZnTe)n.

A Theoretical Analysis of Physical Properties and Half-Metallic Stability under Pressure Effect of the ScNiCrZ (Z=Ga, Al, In) Heusler Alloys

The aim purpose of this study is to investigate the structural, elastic, magnetic, electronic properties and half-metallic stability under pressure of ScNiCrZ ([Formula: see text], Ga and In) quaternary Heusler alloys using full-potential linear muffin-tin orbital (FP-LMTO) method within the gradient generalized approximation (GGA) for exchange, and correlation potential. In order to evaluate the stability of our compounds, the formation energy, and elastic constants have been evaluated. The results showed that our compounds have ferromagnetic ground states and are energetically more stable in type-[Formula: see text] configuration. True half-metallic ferromagnetic behavior with 100% spin polarization at Fermi level [Formula: see text] with high Curie temperature [Formula: see text], and very interesting bandgap in the minority spin are obtained for the three alloys. The calculated total magnetic moment [Formula: see text] for all three alloys is consistent with Slater[Formula: see text]Pauling rule. The half-metallicity is maintained over a wide range of lattice constants making these alloys promising for spintronic, and magneto-electronics applications.

First principles calculation of structural, electronic and optical properties of (001) and (110) growth axis (InN)/(GaN)n superlattices

Based on the full potential linear muffin-tin orbitals (FPLMTO) calculation within density functional theory, we systematically investigate the electronic and optical properties of (100) and (110)-oriented (InN)/(GaN)n zinc-blende superlattice with one InN monolayer and with different numbers of GaN monolayers. Specifically, the electronic band structure calculations and their related features, like the absorption coefficient and refractive index of these systems are computed over a wide photon energy scale up to 20 eV. The effect of periodicity layer numbers n on the band gaps and the optical activity of (InN)/(GaN)n SLs in the both growth axis (001) and (110) are examined and compared. Because of prospective optical aspects of (InN)/(GaN)n such as light-emitting applications, this theoretical study can help the experimental measurements.

A first-principles investigation of band inversion in topologically nontrivial Na2AgX (X= As, Sb and Bi) full Heusler compounds

Topological nontrivial nature are the latest phases to be discovered in condensed matter physics with insulating bulk band gaps and topologically protected metallic surface states; they are one of the current hot topics because of their unique properties and potential applications. In this paper, we have highlighted a first-principles study of the structural stability and electronic behavior of the Na2AgX (X = As, Sb and Bi) full Heusler compounds, using the Full-Potential Linear Muffin-Tin Orbital (FP-LMTO) method. We have originated that the Hg2CuTi structure is appropriate in all studied materials. The negative values of the calculated formation energies mean that these compounds are energetically stable. The band structure is studied for the two cases relating the existence and the absence of spin-orbital couplings, where all materials are shown to be topologically non-trivial compounds. Spin orbital couplings were noticed to have no significant effect on the electronic properties such as the topological order.

Ground state parameters, electronic properties and elastic constants of CaMg3: DFT study

The present study aims to investigate the equation of state (EOS) parameters of CaMg 3 in αReO 3 (D0 9 ), AlFe 3 (D0 3 ), Cu 3 Au (L1 2 ) and CuTi 3 (L6 0 ) structures, using full potential linear muffin-tin orbitals (FP-LMTO) approach based on the density functional theory (DFT). The local density approximation (LDA) and the generalized gradient approximation (GGA) were both applied for the exchange-correlation potential term. The calculated equation of state parameters at equilibrium, in general, agreed well with the available data of the literature. The calculations showed that under compression CaMg 3 transforms from D0 3 to D0 9 at about 29.96 GPa, and 25.1 GPa using LDA and GGA, respectively. The elastic constants C ij , aggregate moduli, Vickers hardness, sound velocity, and Debye temperature of CaMg 3 in D0 3 structure were also reported, discussed and analyzed. Using LDA (GGA), the calculated values of H V and θ D were found at around 5.80 GPa (5.93 GPa) and 393.44 K (389.91 K), respectively. Electronic band structure, total density of states (TDOS) as well as the partial density of states (PDOS) have been also obtained. The electronic band structure confirms the metallic behavior of CaMg 3 in D0 3 phase, the valence bands are dominated by the maximum contribution of ‘ d ’ like states of Ca in the energy ranging from 2 to 3 eV for GGA, and from 4.5 to 5 eV for LDA, respectively.

Insight View of Topological Nontrivial Nature in the Novel Alkali Metal–Based Quaternary Heusler Compounds via Ab Initio Calculations

In this paper, we have highlighted a first-principles study of the structural stability and electronic behavior of the novel alkali metal–based quaternary Heusler compounds (LiNaCuAs, LiKCuAs, NaKCuAs, LiRbCuAs, NaRbCuAs, and KRbCuAs), using the full-potential linear muffin-tin orbital (FP-LMTO) method. The obtained results show that our compounds are energetically more stable in the Hg2CuTi-type structure. The calculated electronic properties with and without spin-orbit coupling (SOC) effects indicate that the majority of compounds naturally present a band inversion order which confirmed the topological nontrivial behavior of these materials. In addition, our results show that SOC is not a primary cause of the band inversion mechanism. The obtained values of the calculated formation energy confirm the physical stability of these compounds against decomposition, and they can be passed in fabrication level.

Ion conduction mechanisms of silver halides under high pressures

ABSTRACT AgI can transform a face-centred cubic lattice structure under pressures in the range 0.4–11.3 GPa. These phases also exhibit high ionic conductivities, particularly at high temperatures. The full-potential linear muffin-tin-orbital (FP-LMTO) method is used to investigate the ion conduction mechanisms of AgI under high pressures, wherein the exchange correlation energies of electrons are calculated via both local density approximation and generalised gradient approximation and then compared. The total energy calculations exhibit saddle points along the migration pathways, where Frenkel defects should be stable. Our results suggest that Frenkel defects do not easily migrate from stable positions, particularly under high pressures. This implies that Frenkel defects dominate ionic conduction not only in AgCl and AgBr, but also in rocksalt-structured AgI.

Electronic Band Structure, Density of States, Phase Transitions, Metallization and Superconducting Transition of KBr under High Pressure

The results of a full potential linear muffin-tin orbital (FP-LMTO) study on the electronic properties of ionic insulator potassium bromide (KBr) under pressure is presented. The phase transition pressure at which the compound undergoes structural phase transition from NaCl to CsCl structure is predicted from the total energy calculations. The ground state properties and band gap values are compared with the experimental results. At normal pressure KBr is a direct band gap insulator. In KBr, the metallization occurs through indirect closing of the band gap between G and H points at the reduced volume V/Vo=0.45 (CsCl structure), the corresponding metallization pressure is 1.274 Mbar. On further increase of pressure, KBr becomes superconductor, and this material comes under the class of electron-phonon-mediated high pressure superconductor. The superconducting transition temperatures (Tc) of KBr is obtained as a function of pressure for both NaCl and CsCl structures. The highest Tc estimated is 5.911 K and the corresponding pressure is 5 Mbar in the NaCl structure and 0.897 K in the CsCl structure. It is also confirmed that the metallization, structural phase transition and onset of superconductivity do not occur simultaneously in ionic compounds. DOI: http://dx.doi.org/10.17807/orbital.v12i2.1401

A Critical Study of Phase Stability and Electronic, Magnetic, and Elastic Properties in the Inverse Heusler Cr2MnSi Alloy: a First-Principles Calculations

Ab initio calculations were systematically investigated for nonmagnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) states of new full-Heusler alloy Cr2MnSi in Hg2CuTi and Cu2MnAl-type structures. The calculations are based on the density functional theory, with the full potential linear muffin-tin orbital (FP-LMTO) method. The results show that the ferromagnetic Hg2CuTi prototype structure is the most stable. The optimized lattice parameter is found to be 5.643 A, with the total magnetic moment 0.30 μB. The electronic band structure calculations revealed that Cr2MnSi exhibits a metallic ferromagnet behavior. Using the Mehl method, we have also calculated the elastic constants and their related parameters such as Poisson’s ratio, Young modulus, Zener anisotropy, shear modulus, Kleinman parameter ξ, Lame constants (λ, μ), Cauchy pressure Pc, microhardness parameter, and the melting temperature Tm. Our calculation validates the conditions of mechanical stability in the cubic crystal. The estimation of the Curie temperature shows that the Cr2MnSi compound is a good candidate for the spintronic application.

First Principle Investigation on the Magnetism of Zinc Blende Structures of 3d (Cr, V, Mn, Cu, Sc)-Doped CdS

Our aim in this paper is to study the influence of doping with transition metals (TM) on the physical properties of CdS. Thus, the structure stability, half-metallic ferromagnetic, and electronic properties of Cr-, V-, Mn-, Cu-, and Sc-doped CdS, at x = 0.0625 concentration have been investigated using first principle calculations based on the density functional theory (DFT). The all-electron full-potential linear Muffin-Tin orbital (FP-LMTO) method and the generalized gradient approximation (GGA) have been employed. The electronic properties indicate that the Cd0.9375Cu0.0625S and Cd0.9375Sc0.0625S compounds are magnetic degenerate semiconductors and the Cd0.9375Mn0.0625S compound is p-type magnetic semiconductor, while the Cd0.9375Cr0.0625S and Cd0.9375V0.0625S compounds are half-metallic ferromagnets. We have also found that the TM-3d states are responsible for the spin-polarization and the induction of magnetic moments in these compounds. Additionally, to explain the origin of half-metallic ferromagnetism, we have calculated the exchange splitting energy Δx(pd) and the exchange constants N0α and N0β. The calculated values suggest that the Cd0.9375Cr0.0625S and Cd0.9375VV0.0625S compounds may be useful for the development of spintronic devices.

Dirac's equation and its implications for density functional theory based calculations of materials containing heavy elements

Electronic structure calculations based on density functional theory (DFT) give quantitatively accurate predictions of properties of most materials containing light elements. For heavy materials, and in particular for $f$-electron systems, DFT based methods can fail both qualitatively and quantitatively for two distinct reasons: their failure to describe confinement effects arising from localized $f$-electron behavior and their incomplete or approximate treatment of relativity. In addition, different methods for incorporating relativistic effects, which give identical results in most light materials, can give different predictions in heavy elements. In order to develop a quantitative capability for calculating the properties of these materials, it is essential to separate the predictions of the underlying equations from the uncertainty introduced in approximations used in computation. Working toward that goal, we have developed a code, called dirac-fp, which is based directly on solving the Dirac-Kohn-Sham equations and uses the full-potential linear muffin-tin orbital (FP-LMTO) approach to electronic structure. In order to assess the performance of dirac-fp, we perform calculations on three different face-centered cubic materials using different approximate treatments of relativity: the scalar relativistic (SR) approach commonly used in most solid-state DFT codes, the scalar relativistic plus spin-orbit coupling corrections (SR+SO) approach which includes spin-orbit coupling self-consistently using the SR states inside the muffin tins, and the Dirac-Kohn-Sham (Dirac) approach implemented in dirac-fp. Performing calculations on thorium, in which relativistic effects should be strong, aluminum, in which relativistic effects should be negligible, and gold, in which relativistic effects play an intermediate role, we find that the Dirac approach is able to provide theoretically consistent results in the electronic structure and ground-state properties across all three materials.

Mechanical stability and optoelectronic behavior of BeXP2 (X=Si and Ge) chalcopyrite

We have conducted a first-principles study on the structural, electronic, optical and elastic properties of BeSiP2 and BeGeP2 chalcopyrite compounds. Using the density functional theory (DFT), implemented in both full potential linear muffin-tin orbital (FP-LMTO) and Vienna Ab initio simulation (VASP) packages. The FP-LMTO is used for the determination of the structural, electronic and optical properties, while the VASP is used to determine the elastic constants that give indications about the material stability. The obtained equilibrium structural parameters are in good agreement with available results. An investigation of the band gap indicates that our compounds possess a semiconductor behavior with direct band gap for BeSiP2 and with an indirect band gap for BeGeP2. The energy band gaps decreased by changing Be atoms from Si to Ge. We have calculated the dielectric function ε(ω). The obtained results show that these materials are promising semiconductors for photovoltaic applications. For the elastic properties, the single-crystal elastic constants Cij, shear anisotropic factors A, as well as polycrystalline bulk, shear and Young's modulus (B, G and E) and Poisson's ratio v have been predicted. The generalized elastic stability criteria for a tetragonal crystal are well satisfied, indicating that BeSiP2 and BeGeP2 are mechanically stable in the chalcopyrite structure.

High pressure-induced phase transitions in AgI semiconducting compound up to 1 Mbar

In this work, we have resorted to a recent version of the full potential linear muffin-tin orbitals (FP-LMTO) method based on the density functional theory (DFT), within both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the calculation of the equilibrium structural parameters, and phase transition under high pressure of AgI semiconducting compound. Results are given for lattice parameters, bulk modulus and its first pressure derivative in different structures. In general, the use of the GGA approach in this work appears more appropriate than the LDA, and it is most correctly predicts the majority of the ground state properties for AgI material. The energy differences of NiAs (B81)/NaCl (B1) phases are around 1.76 and 1.15 meV, using the LDA and the GGA, respectively. Importantly, the phase transitions for this material from sixfolds coordinated NaCl-type structure (B1) to the eightfold coordinated CsCl-type structure (B2), and then to the hexagonal close packed HCP-type structure (A3) are possible under high pressure. Our calculations show that AgI semiconducting compound transforms firstly from B1 to B2 at pressure of around 55.58 GPa, and then from B2 to A3 at pressure of around 95.03 GPa, respectively.

First-principles calculations to investigate structural and thermodynamic properties of Ni2LaZ (Z = As, Sb and Bi) Heusler alloys

Structural, electronic, elastic and thermodynamic properties of Ni2LaZ (Z = As, Sb and Bi) Heusler alloys based on rare earth element have been investigated using full-potential linear muffin-tin orbital (FP-LMTO) method within generalized gradient approximation (GGA) in the frame of density functional theory (DFT). By using total energy variations, the independent elastic constants and their pressure dependence have been determined. Also, anisotropic parameter (A), shear modulus (G), Young modulus (E), Poisson’s ratio (ν), ratio (B/G) are calculated. Using quasi-harmonic Debye model, thermodynamic properties of Ni2LaZ (Z = As, Sb and Bi) Heusler alloys are investigated in temperature range 0–1200 K and pressure range 0–50 GPa. The temperature and pressure effects on the unit cell volume, bulk modulus (B), heat capacities (Cv) at stable volume, (Cp), Debye temperatures (θD), Gibbs energies (G), thermal expansion coefficients (α) and entropies (S) are determined from non-equilibrium Gibbs functions. This study allows to understand deeply the structural and thermodynamic properties of Ni2LaZ (Z = As, Sb and Bi) Heusler alloys in shortest time and cost-effective.

First-principles investigation of the structural, elastic, electronic, and optical properties of semiconducting AgBr1–xIx (0 ≤ x ≤ 1) ternary alloys in rock-salt and zinc blende structures

In this work, first principle calculations of the structural, electronic, elastic, and optical properties of novel AgBr1–xIx ternary alloys in rock-salt (B1) and zinc-blende (B3) structures are presented. The calculations were performed using the full-potential linear muffin-tin orbital (FP-LMTO) method within the framework of the density functional theory (DFT). The exchange and correlation potentials were treated according to the local density approximation (LDA). The lattice constants for the B1 and B3 phases versus iodide concentration (x) were found to deviate slightly from the linear relationship of Vegard’s law. The calculated electronic properties showed that AgBr1–xIx alloys in the B3 structure have a direct band gap (Γ – Γ) for all concentrations of x, which means that they can be used in long-wavelength optoelectronic applications, while in the B1 structure they have an indirect (Γ – R) band gap. The elastic constants Cij, shear modulus G, Young’s modulus E, Poisson’s ratio ν, index of ductility B/G, sound velocities vt, vl, and vm, and Debye temperature θD were also reported and analyzed. By incorporating the basic optical properties, we discussed the dielectric function, refractive index, optical reflectivity, absorption coefficient, and optical conductivity in terms of incident photon energy up to 13.5 eV. The present results were found to be in good agreement with the available experimental and other theoretical results.

The CeFe11Ti permanent magnet: a closer look at the microstructure of the compound

High-performance permanent magnets (PM) are compounds with outstanding intrinsic magnetic properties. Most PMs are obtained from a favorable combination of rare earth metals (RE = Nd, Pr, Ce) with transition metals (TM = Fe, Co). Amongst them, CeFe11Ti claims considerable attention due to its large Curie temperature, saturation magnetization, and significant magnetocrystalline anisotropic energy. CeFe11Ti has several potential applications, in particular, in the development of electric motors for future automatic electrification. In this work, we shed some light on the mictrostructure of this compound by performing periodic hybrid-exchange density functional theory (DFT) calculations. We use a combined approach of atom-centered local orbitals, plane waves and full-potential linear muffin-tin orbital (LMTO) for our computations. The electronic configuration of the atoms involved in different steps of formation of the crystal structure of CeFe11Ti gives an explanation on the effect of Ce and Ti on its magnetic properties. While Ti stabilizes the structure, atomic orbitals of Ce hybridizes with Fe atomic orbitals to a significant extent and alters the electronic bands. Our calculations confirm a valence of 3+ for Ce, which has been deemed crucial to obtain a large magnetocrystalline anisotropy. In addition, we analyze several spin configurations, with the ferromagnetic configuration being most stable. We compare and contrast our data to those available and provide an insight for further development of optimized high-performance PMs. Moreover, we compute the Magnetocrystalline Anisotropy of this compound by means of two approaches: the Force Theorem and a full-potential LMTO method.