Linear Muffin-tin Orbital Method Research Articles

Theoretical Investigations of Ti-Based Binary Shape Memory Alloys

The electronic structure and ground state properties of TiX (X = Fe, Ni, Pd, Pt and Cu) type Shape Memory alloys have been calculated using the self consistent Tight- Binding Linear Muffin Tin Orbital (TB-LMTO) method. The systematic total energy studies made on TiX alloys in both B2 and (B19/B19’) structures successfully explain the structural stability of these compounds. The equilibrium lattice parameters, bulk moduli (Bo), cohesive energy (Ecoh) and heat of formation (ΔH) are calculated for these systems and compared with the available experimental and other theoretical results. The bonding nature of these TiX alloys is analyzed via the density of states (DOS) histogram.

First-principles Study of Nitrogen Vacancies in GdN

ABSTRACTThe electronic structure of nitrogen vacancies in gadolinium nitride are studied using the full-potential linearized muffin-tin orbital method in the local spin density approximation with Hubbard U corrections (LSDA+U). The vacancy is found to have two localized defect levels in the gap, one of each spin. The third electron of each vacancy in the neutral state dopes the conduction band. The single positive state is found to be the ground state for Fermi levels located anywhere within the band gap. The vacancy has a net magnetic moment of 1 μB in the neutral charge state. The presence of the vacancy is found to increase the average exchange interactions between Gd atoms and hence the Curie temperature but only by about a factor 2 compared to GdN without vacancies.

Spin-dependent Electrical Resistivity in Ferromagnets by Magnetic Fluctuations

Spin-dependent electrical resistivities ρ↑, ρ↓ of bcc-Fe based on scattering due to magnetic fluctuation below the Curie temperature were calculated using first-principles methods. The tight-binding linear muffin-tin orbital method with local spin-density approximation was employed to calculate the electronic structure. The spin fluctuations within the static (adiabatic) approximation corresponded to the local spin disorder, which can be treated using the coherent potential approximation. The Kubo-Greenwood formula was used to calculate the electrical resistivity in each spin state based on the electron scattering by magnetic fluctuations. The obtained results indicated that the ferromagnetic states of bcc-Fe in finite temperature are characterized as a classical spin system such as the Heisenberg model, although the electronic structure calculations are carried within the itinerant electrons system. The total electrical resistivities ρ = ρ↑ρ↓/(ρ↑ + ρ↓) which are on the basis of the two-current model show qualitative agreement with the experimental measurement as a function of temperature. Furthermore, the spin asymmetry coefficients β = -(ρ↑ - ρ↓)(ρ↑ + ρ↓) exhibited a remarkable behavior that the sign changed from positive to negative in the finite temperature region below the Curie temperature.

Site Dependence of Electronic Structure of Gd Impurities in GaN

ABSTRACTElectronic structure calculations are reported for Gd in GaN on Ga as well as on N site and for pairs of Gd on neighboring Ga and N sites, using the full-potential linearized muffin-tin orbital method in the local spin density approximation with Hubbard U corrections (LSDA+U). The energy of formation for the N site is found to be much higher than for the Ga site even after relaxations are included. The GdN configuration is found to be at best metastable (in ZB). In WZ and in the pair configurations, the Gd is found to move toward an interstitial site leaving a nitrogen vacancy behind. The electronic structure of these structures and their magnetic moments are discussed.

First-principles study for electronic structure and physical property of Co-based Heusler alloys

The statistical investigation of the physical property of Co-based Heusler alloys with the atomic composition or configuration dependence are carried out in first-principles approach. In particular, the electronic structure, magnetic moment and electrical resistivity due to disorder alloy effects of Co2MnAl1−zSiz (0.0 < z < 1.0) and Co2Mn1−yFeySi (0.0 < y < 1.0) with the L21, B2 and A2 structure are calculated by using the tight-binding linear muffin-tin orbital method combined with the coherent potential approximation based on the local spin-density functional approximation and by using the Kubo-Greenwood formula, respectively. The obtained results indicate that these properties of the Co-based Heusler alloys significantly depend on the atomic configuration and composition, especially, they are sensitive to the existence of the half-metallic property.

AB INITIO APPROACH TO STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF B-, C- AND N-DOPED ANATASE

The effect of doping with boron, carbon and nitrogen on crystal lattice parameters, electronic band structure and optical absorption of anatase has been studied by means of an ab initio density functional theory approach. The investigations included optimization of crystal structure based on the pseudo-potential plane-wave approach. The spin-polarized calculations of the band structure with the account of on-site Coulomb correlations (LSDA+U) employing the tight-binding linear muffin-tin orbitals method (TB-LMTO) have also been performed. The evaluations of optical absorption were based on the calculations of dielectric function with local field effects taken into account. We find that the crystal lattice relaxation around the doping atoms produces noticeable changes in the band structure, magnetic state and optical properties of the doped compounds. The most considerable effects are the collapse of magnetic moment on carbon atom and an essential reduction of the optical absorption in the region of the impurity band — impurity band transitions. Comparing optical absorption for different kinds of doping and taking into account the intensity distribution of the solar light we come to the conclusion than the doping with boron is the most promising kind of doping for photocatalytic applications of the doped anatase.

Structural and electronic properties of bulk GaP and AlP and their [formula omitted] superlattices

The structural and the electronic properties of binary GaP and AlP compounds and their ( GaP ) n / ( AlP ) n superlattices are investigated using the recent version of the first-principles full potential linear muffin-tin orbitals method (FP-LMTO) (Lmtart 7.0). The structural parameters and the pressures at which these compounds undergo structural phase transition from zinc-blende (B3) to the rocksalt (B1) are determined. From the results of the electronic properties we find that the parent materials (GaP, AlP) have indirect bandgaps. The resemblances between GaP and AlP and their small lattice mismatch led us to perform investigations on zinc-blende/zinc-blende ( GaP ) n / ( AlP ) n for n = 1 , 2 and 3 monolayer. Our calculations performed for band structure and density of state show an indirect band gap superlattices for n = 1 and 2 and a direct band gap for n = 3 . Details of the electronic structure of superlattices are discussed. An excellent agreement was found between our results and those of other theoretical predictions and experimental measurements.

Electronic and thermal properties of B 2-type AlRE intermetallic compounds: A first principles study

The ground state electronic structure and thermal properties of B 2-type intermetallic compounds AlRE (RE: Pm, Sm, Eu, Tb, Gd and Dy) have been studied using a self-consistent tight-binding linear muffin-tin orbital (TB-LMTO) method at ambient as well as at high pressure. These compounds show metallic behavior under ambient condition. The band structure, total energy, density of states and ground state properties like lattice parameter, bulk modulus are calculated in the present work. The Debye–Grüneisen model is used to calculate the Debye temperature and the Grüneisen constant. The calculated results are in good agreement with the reported experimental and other theoretical results. The variation in the Debye temperature with pressure has also been reported. We present a detailed analysis of the role of f electrons of RE in the AlRE system.

Magnetic phase diagram for CuMn

To study the magnetic phases of CuMn, we carry out a generalized perturbation expansion of the band energy across the composition range. We obtain the pair energy using the orbital peeling technique of Burke, based on the tight-binding linear muffin-tin orbital and augmented space recursion methods. We analyze the phases of the system by studying the probability distribution of the local staggered occupation ’fields’ within a mean-field approach. We show that our predicted phase boundaries agree well with experimental results.

Investigations on cobalt doped GaN for spintronic applications

(Ga1−xCox)N was synthesized at 1223K using pure gallium and cobalt metal as precursors in a reactor specially designed for this purpose with ammonia as the nitrogen source. The structural confirmation of wurtzite phase of GaN is done using powder X-ray diffractometer. Photoluminescence shows red shift in band edge emission as the cobalt concentration increases from 1 to 5 atomic percentage together with nitrogen related vacancy emission at 3.24eV and cobalt related emission at 3.13eV. The magnetic properties were studied at 10K using superconducting quantum interface device (SQUID). The obtained maximum magnetic moments for 1%, 3% and 5% cobalt doped GaN are 1.63, 0.21 and 0.14μB, respectively. The decrease in magnetic moment with increase in dopant concentration may be due to the formation of secondary phases or cobalt cluster, which contributes to anti-ferromagnetism. From temperature dependent magnetization measurements it is observed that there is no drastic change in the magnetic moment upto room temperature for 1% cobalt doped GaN. Theoretical calculations based on the density functional theory within Tight Binding Linear Muffin-tin Orbital (TBLMTO) method has been carried out to study the magnetic properties of cobalt doped GaN. The obtained magnetic moment values per Co atom are 2.56μB for 1.56% and 2.77% and 1.50μB for 4.20%. This is found to be higher when compared with experimental values and this difference is explained based on structural defects and percentage of dopant used during synthesis. The half metallic behavior is observed for 1.56% and 2.77% Co dopants, but for higher percentage of dopant the system becomes metallic. Hence, it is concluded that only lower percentage of cobalt doped GaN is suitable for spintronic applications.

Cis-trans Germanium chains in the intermetallic compounds ALi 1– xIn xGe 2 and A2(Li 1– xIn x) 2Ge 3 ( A=Sr, Ba, Eu)—experimental and theoreticalstudies

Two types of strontium-, barium- and europium-containing germanides have been synthesized using high temperature reactions and characterized by single-crystal X-ray diffraction. All reported compounds also contain mixed-occupied Li and In atoms, resulting in quaternary phases with narrow homogeneity ranges. The first type comprises EuLi 0.91(1)In 0.09Ge 2, SrLi 0.95(1)In 0.05Ge 2 and BaLi 0.99(1)In 0.01Ge 2, which crystallize in the orthorhombic space group Pnma (BaLi 0.9Mg 0.1Si 2 structure type, Pearson code oP16). The lattice parameters are a=7.129(4)–7.405(4) Å; b=4.426(3)–4.638(2) Å; and c=11.462(7)–11.872(6) Å. The second type includes Eu 2Li 1.36(1)In 0.64Ge 3 and Sr 2Li 1.45(1)In 0.55Ge 3, which adopt the orthorhombic space group Cmcm (Ce 2Li 2Ge 3 structure type, Pearson code oC28) with lattice parameters a=4.534(2)–4.618(2) Å; b=19.347(8)–19.685(9) Å; and c=7.164(3)–7.260(3) Å. The polyanionic sub-structures in both cases feature one-dimensional Ge chains with alternating Ge–Ge bonds in cis- and trans-conformation. Theoretical studies using the tight-binding linear muffin-tin orbital (LMTO) method provide the rationale for optimizing the overall bonding by diminishing the π– p delocalization along the Ge chains, accounting for the experimentally confirmed substitution of Li forIn.

BaGa2Pn2 (Pn = P, As): New Semiconducting Phosphides and Arsenides with Layered Structures

Reported are the synthesis, the structural characterization, and the electronic band structures of two new Zintl phases: BaGa2P2 and BaGa2As2. Both compounds are isoelectronic and isotypic and crystallize in a monoclinic system with a new structure type (Pearson symbol mP20). The structures have been established by single-crystal X-ray diffraction, space group P2(1)/c (Z = 4), with lattice parameters as follows: a = 7.3363(13)/7.495(5) Å; b = 9.6648(17)/9.901(6) Å; c = 7.4261(13)/7.643(5) Å; beta = 115.373(2) degrees/115.381(8) degrees for BaGa2P2/BaGa2As2, respectively. The atomic arrangements in both cases are devoid of disorder and are best rationalized as polyanionic layers, (infinity)(2)[Ga2Pn2]2- (Pn = P, As), with Ba2+ cations separating them. The layers, in turn, can be viewed as the result of condensation of Ga2Pn6 units, which are isosteric with the ethane molecule in its staggered conformation. Structural parallels with other known Zintl phases are presented. The electronic structures, computed using the tight-binding linear muffin-tin orbital methods (TB-LMTO), are discussed as well.

Theoretical study of electronic, magnetic and structural properties of Mo and W based group V (N, P, As, Sb and Bi) compounds

Magnetic and electronic structure calculations were carried out for WC-, MnP-, NaCl- and zinc blende (ZB)-type Mo and W based group V compounds, TMX (TM = Mo and W; X = N, P, As, Sb and Bi), using the tight-binding linear muffin-tin orbital (TB-LMTO) method. For these compounds in these four structures, the total energy has been calculated as a function of volume in spin-polarization and non-spin-polarization calculations. From the total energy calculations, it is observed that these compounds favour the structures for which there is octahedral co-ordination for the anion rather than tetrahedral co-ordination. For the large volume expansion, these compounds prefer tetrahedral co-ordination compared to octahedral co-ordination. Moreover, these compounds in the ZB-type structure are found to exhibit half-metallic property with a magnetic moment of 3.00 μ B per formula unit under expansion of volume. The equilibrium lattice constant, bulk modulus, heat of formation, magnetic moment, spin-flip-gap and minority spin bandgap are calculated and compared with available results. The band structure and density of states are presented.

Dynamical mean-field theory within the full-potential methods: Electronic structure ofCeIrIn5,CeCoIn5, andCeRhIn5

We implemented the charge self-consistent combination of density-functional theory and dynamical mean-field theory (DMFT) in two full-potential methods, the augmented plane-wave and the linear muffin-tin orbital methods. We categorize the commonly used projection methods in terms of the causality of the resulting DMFT equations and the amount of partial spectral weight retained. The detailed flow of the dynamical mean-field algorithm is described, including the computation of response functions such as transport coefficients. We discuss the implementation of the impurity solvers based on hybridization expansion and an analytic continuation method for self-energy. We also derive the formalism for the bold continuous time quantum Monte Carlo method. We test our method on a classic problem in strongly correlated physics, the isostructural transition in Ce metal. We apply our method to the class of heavy-fermion materials ${\text{CeIrIn}}_{5}$, ${\text{CeCoIn}}_{5}$, and ${\text{CeRhIn}}_{5}$ and show that the $\text{Ce}\text{ }4f$ electrons are more localized in ${\text{CeRhIn}}_{5}$ than in the other two, a result corroborated by experiment. We show that ${\text{CeIrIn}}_{5}$ is the most itinerant and has a very anisotropic hybridization, pointing mostly toward the out-of-plane In atoms. In ${\text{CeRhIn}}_{5}$ we stabilized the antiferromagnetic DMFT solution below 3 K, in close agreement with the experimental Neel temperature.

Ab initioelectronic structure calculation of disorder ternary alloys: A reciprocal-space formulation

Using first-principles density-functional calculations, we present a formalism for a reciprocal-space study of the electronic structure of random ternary alloys. The formalism is based on the augmented-space recursion introduced earlier by us in conjunction with the tight-binding linearized muffin-tin orbital method. Emphasis shall be given to the configurationally averaged Bloch spectral function, which will be a key quantity of our formalism and the reflection of its nature on the density of states will be discussed. We showcase the feasibility of our formalism by applying to two different alloy systems namely: face-centered-cubic based ${\text{Cu}}_{1\ensuremath{-}x\ensuremath{-}y}{\text{Ni}}_{x}{\text{Zn}}_{y}$ alloy and the series of disordered ternary Invar alloys, ${\text{Fe}}_{1\ensuremath{-}x\ensuremath{-}y}{\text{Ni}}_{x}{X}_{y}$ $[X=\text{Co},\text{Pd},\text{Pt}]$. The effects of short-range ordering and the magnetic properties of these alloys will be discussed in some detail and it will be shown that our predicted magnetic moment agrees well with earlier results.

Pressure-induced structural phase transition and electronic properties of actinide nitrides: Ab initio calculations

We report ab initio calculations of pressure-induced structural phase transition and electronic properties of the NaCl-type actinide nitrides namely AnN (An=Np and Cm). The total energy as a function of volume is obtained using the self-consistent tight-binding linear muffin tin orbital (TB-LMTO) method by performing spin and non-spin-polarized calculations. Magnetically the AnN compounds are stable in ferromagnetic (FM) state at ambient condition. From the present study, we predict a structural phase transition from ferromagnetic (FM) NaCl-type (B 1 phase) structure to ferromagnetic CsCl-type (B 2 phase) structure for these in the pressure range of 80.0–50.0 GPa. The pressure-induced transition is found to be first order. The band structure and density of states (DOS) are reported in both FM-B 1 phase and FM-B 2 phase. The ground-state properties such as magnetic moment, lattice parameter and bulk modulus are calculated and compared with the available theoretical and experimental results.

Structure and magnetism of pseudobinary L1 alloy FePtM(M=Ir,Au)

We performed energy-band calculations for the L10 pseudobinary bulk alloy FePt1−xMx(M=Ir,Au) by using the linear muffin-tin orbital method with atomic sphere approximations. The exchange-correlation potential was treated within the generalized gradient approximation. The total energies for the ferromagnetic (FM) and three kinds of antiferromagnetic (AFM) states were estimated as a function of lattice ratio c/a∗. For 5d atom substitution, we adopted a virtual crystal approximation. On the basis of the minimum of the total energy, we present the following result: a change in magnetic state (FM-AFM) occurs around FePt1−xMx. It is pointed out that the magnetic state change also depends on the number of valence electrons.

Calculated valence electronic structure of 3d metals for use in the X-ray intensity ratio studies

3d occupation numbers of the transition elements corresponding to various types of atomic configurations are calculated by means of the linear muffin-tin orbital (LMTO) method. This data is used with the multiconfiguration Dirac–Fock (MCDF) X-ray intensity ratios to estimate the electron populations of the 3d metals in alloys.

Pressure-induced phase transition and electronic structure of curium pnictides: Ab initio calculations

We report an ab initio calculation of pressure-induced structural phase transition and electronic properties of the NaCl-type Cm-based pnictides namely CmX (X = N, P, As, Sb and Bi). The total energy as a function of volume is obtained by means of self-consistent tight-binding linear muffin tin orbital (TB-LMTO) method by performing spin and non-spin polarized calculation. Magnetically the CmX compounds are stable in ferromagnetic (FM) state and their crystal structure is NaCl-type at ambient condition. From the present study, we predict a structural phase transition from ferromagnetic (FM) NaCl-type ( B 1 phase) structure to ferromagnetic CsCl-type ( B 2 phase) structure for curium pnictides in the pressure range of 51.0–10.0 GPa (CmN to CmBi). The pressure-induced transition is found to be first order. The band structure and density of states (DOS) are plotted in FM- B 1 phase and FM- B 2 phase. Apart from this the ground-state properties like magnetic moment, lattice parameter and bulk modulus are calculated and compared with the available theoretical and experimental results.

Study of electronic and structural properties of half metallic rare earth mononitrides

In the present work we investigated theoretically the electronic, magnetic and structural properties of two rare-earth nitrides (REN: RE = Sm, Eu) by using self- consistent tight-binding linear muffin tin orbital (TBLMTO) method. Magnetically, both the rare earth nitrides (RENs) are stable in ferromagnetic (FM) state, while its ambient structure is found to be stable in NaCl-type (B1) structure. From the present study we predict the pressure induced structural phase transition in both RENs from the relatively open NaCl-type structure into more dense CsCl-type structure at 8.6 GPa and 14.6 GPa respectively. They form a new class of half-metallic magnets with high magnetic moments and are strong candidates for applications in spintronics and spinfiltering devices. We have therefore, calculated electronic band structures, equilibrium lattice constants, cohesive energies, bulk moduli and magnetic moments for REN compounds in both B1 and B2 phases.