Exact Muffin-tin Orbitals Method Research Articles

Effects of Ta on the Structural, mechanical and electronic properties of the ternary alloys [formula omitted]: A computational study

The structural, elastic and electronic properties of the ternary transition metal nitrides alloys TaxHf1−xN at (0<x<1) in the rock-salt structure are investigated by ab initio calculations. The calculations were performed using the first-principles Exact Muffin-Tin Orbitals method using full charge density technique within the framework of density functional theory. The compositional disorder is treated within the coherent potential approximation. The estimated formation enthalpy indicates that Ta0.5Hf0.5N is thermodynamically the most stable alloy. The obtained lattice parameters of the TaxHf1−xN alloys are in good agreement with other available theoretical and experimental values. The predicted elastic stiffness constants C11, C12 and C44 indicate that the TaxHf1−xN alloys are mechanically stable and the addition of Ta increases their ductility. The Ta0.7Hf0.3N found to be hardest alloy. The correlation between Pettifor’s criterion (C12−C44) normalized by bulk modulus B and Pugh’s ratio G/B with increasing the degree of alloying x allowed us to predict that the critical value (G/B)=0.53, which correspond to x around 0.6±0.05, marks the brittle to ductile transition.

Exploration of high-ductility ternary refractory complex concentrated alloys using first-principles calculations and machine learning

BCC-based refractory complex concentrated alloys (RCCAs) are attracting attention as high-temperature materials because of their exceptional strength at high temperatures, but suffer from low tensile ductility. To search for alloys with improved ductility, it is necessary to investigate the properties of RCCA systems thoroughly, however, an experimental investigation of these vast constitutional spaces is impractical. This study employed data-driven approaches that combined first-principles calculations with machine learning. We first calculated the lattice parameters and elastic constants of 1693 ternary RCCAs, subsets of RCCAs alloys consisting of Ti, Zr, Hf, Nb, Mo, V, Ta, and W, using the exact muffin-tin orbitals method with coherent potential approximation (EMTO-CPA), and generated ductility-related parameters, including Pugh's ratio, Poisson's ratio, and Cauchy pressure. Machine learning models that could predict the three parameters were searched and trained using the generated data. Subsequently, an inverse design based on optimization algorithms was performed to identify optimal alloy systems with high Pugh's ratios. The ductility of the searched alloys was verified by calculating Pugh's ratio using EMTO-CPA, followed by thermodynamic calculations to investigate their structural stability.

Phase stability and elastic properties of NbMoTaWMx (M = Al, V, Zr, Tc, Re and Ir) RHEAs: A first-principles assessment

Using the exact muffin-tin orbital (EMTO) method in combination with the coherent potential approximation (CPA), we studied the influence of alloying elements Al, V, Zr, Tc, Re and Ir on the phase stability, lattice parameters, densities, and elastic properties of NbMoTaWMx (M = Al, V, Zr, Tc, Re, Ir; 0 ≤ x ≤ 1.0) refractory high entropy alloys. The predicted lattice parameter and elastic parameters agree with the available experimental and theoretical data. We calculated the atomic size difference (δ), the valence electron concentration (VEC) and the total energy of face-centered cubic (fcc), body-centered cubic (bcc) and hexagonal closed-pack (hcp) structures. We found that all studied NbMoTaWMx (M = Al, V, Zr, Tc, Re, Ir; 0 ≤ x ≤ 1.0) systems have the bcc structure. We showed that Al and Ir decrease the stability of the bcc structure and Zr significantly enlarges the lattice parameter of the host. Vanadium increases the ductility of NbMoTaW system. On the other hand, Al and Ir have strongly non-linear effect on the ductility, with clear minimum at x = 0.55. The present results provide consistent theoretical data and call for experimental investigation for these alloys.

Chemical ordering induced elastic hardening and thermoelastic properties of β phase Mg1-xScx lightweight shape memory alloys

The effect of chemical ordering on the thermoelastic properties of Mg-Sc light weight shape memory alloys are studied by the exact muffin-tinorbital method. Chemical ordering has significant hardening effect on elastic properties of Mg-Sc alloys, the C' is increased by 21% for Mg76Sc24 alloy, and the elastic hardening due to ordering can properly explain the increase in Vickers hardness observed in experiment. The quasi-harmonic Debye-Grüneisen model simulated the order–disorder transition temperature reasonably. The vibrational entropy increase due to elastic softening induced by disordering contributes considerably in driving the order–disorder transition. Mg-Sc alloys in ordered phase shows better thermoelastic stability over well-known commercial Mg alloys, therefore, ordering treatment of Mg-Sc are beneficial for structural application of this family of alloys. The Sc atoms (Mg atoms either) in bcc nearest neighboring lattice repel each other to form a B2-type ordered phase, and resultantly, the s-d and p-d hybridization between nearest neighboring Mg and Sc atoms is the main electronic reason for elastic hardening. The findings in current article not only give insight into understanding the strengthening mechanism during the ordering process of Mg-Sc alloys, but also provides a useful reference for the future development and modification of their shape memory effects.

First-principles study of the phase stability and elastic properties of TiVNbMoM (M = Al, Sc, Ni and Cu) high entropy alloys

The ab initio exact muffin-tin orbitals (EMTO) method in combination with the coherent potential approximation (CPA) were used to study the influence of alloying elements M = Al, Sc, Ni and Cu on the phase stability, lattice constants, elastic constants, polycrystalline elastic moduli and electronic structure of equiatomic and non-equiatomic TiVNbMoM refractory high entropy alloys. The agreement between our results and the available experimental and theoretical data is quite good. It was found that the equiatomic systems are stable in the body-centered cubic (bcc) structure. Alloying elements decrease the stability of the bcc against the face-centered cubic (fcc) and the hexagonal close-packed (hcp) structures. Scandium enlarges the lattice constants of equiatomic and non-equiatomic systems significantly. According to the calculated bulk modulus to shear modulus, Poisson’s ratio and Vickers hardness, all studied equiatomic and non-equiaomic systems are found to be ductile. However, alloying elements Al, Ni and Cu reduce the ductility and improve the hardness of equiatomic and non-equiatomic TiVNbMoM systems, while the ductility (hardness) of non-equiatomic systems enhances (reduces) by substitution with Sc element. The present theoretical results provide insight for the design and improvement of high entropy alloys and complete information on the alloying effects.

Fully relativistic first-principles quantum transport simulation of noncollinear spin transfer and spin Hall current

In this work, we report the fully relativistic (FR) first-principles quantum transport simulation of noncollinear spin transfer and spin Hall current in the device structure. In this method, the noncollinear FR exact muffin-tin orbital method is combined with Keldysh's nonequilibrium Green's function approach and mean-field theory to account for the multiple disorder scattering. We adopt the Bargmann-Wigner polarization operator to define the appropriate FR spin current so that the current-induced spin transfer, in the noncollinear magnetic device or due to the spin Hall effect, can be studied from first principles. As applications, we calculate the spin transfer torque in noncollinear spin valves Co/Cu/FM/Cu (FM = Co, ${\mathrm{Ni}}_{0.8}{\mathrm{Fe}}_{0.2}$) and spin Hall angles in various ${\mathrm{Pt}}_{1\ensuremath{-}x}{Y}_{x}$ [$Y$ = vacancy (Va), Au, Ag, Pd] alloys. We find that our FR results agree well with previous theoretical simulations and experimental measurements. Moreover, it is found that the applied finite bias can significantly enhance the spin Hall angle in ${\mathrm{Pt}}_{1\ensuremath{-}x}{\mathrm{Va}}_{x}$, and PtAg alloy presents a much higher spin Hall angle than that of PtAu and PtPd alloys. Our implementation of the FR method provides an important first-principles tool for studying various nonequilibrium spin phenomena and the associated relativistic effects in realistic device structures with atomic disorders, including both current-induced spin transfer and spin-orbit torques.

Predicting elastic properties of refractory high-entropy alloys via machine-learning approach

Refractory high entropy alloy (RHEA) is an important family of alloy with excellent mechanical properties and broad industrial applications. Different chemical and stoichiometric compositions make RHEA a highly tunable material with a huge space for optimization. However, the virtual screening of RHEA is extremely nontrivial, considering the high cost of conventional first-principles calculations. In this work, we compute the ground state and the elastic properties of 2487 RHEAs using exact muffin-tin orbital method combined with coherent potential approximation (EMTO-CPA). Using these data, we train an accurate and robust random forest model that can predict the elastic properties of RHEA systems much more efficiently. Furthermore, we also examine the correlation between seven independent input features and the elastic properties of the alloy. Through this analysis, we identify the most important features that control the elastic properties of RHEA, paving the road to a rational design of the RHEA materials.

Crystal structure and site preference, magnetic and elastic properties, and martensitic transformation of Ni- and Fe-doped Co2VGa alloys: A first-principles study

Using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, the crystal structure and site preference, magnetic and elastic properties, and martensitic transformation (MT) are systematically investigated with the three groups of Heusler alloys: (Co2−xMx)VGa (M1x), Co2(V1−xMx)Ga (M2x), and Co2V(Ga1−xMx) (M3x, M = Ni and Fe, 0≤x≤1.0). It is shown that instead of the L21 and XA structures, the fcc one is energetically preferred in the cubic M3x (x≥0.8) alloys. In L21-Ni2x (x≤0.6) and fcc-Ni3x (x=0.8), Ni atoms even prefer the Ga and Co anti-sites, respectively, and the replaced atoms move to the sublattices of the deficient ones. Their total magnetic moment is dominated by the magnetic exchange interactions corresponding to the pairs of two Co atoms on the different sublattices in M = Ni and Fe1x, Co and Fe in Fe2x and Fe3x (x&amp;lt;0.8), and Fe and Fe atoms in Fe3x (x≥0.8) alloys, respectively. These Ni1x, Ni2x, and Fe3x with x≥0.4 as well as Ni3x with x≥0.2 alloys are predicted having the MT behavior and also the better mechanical property relative to Co2VGa. A lower shear modulus (C′=(C11−C12)/2) generally corresponds to a higher MT temperature, and these alloys, which can undergo the MT are further evaluated with C′&amp;lt;36.50 GPa. Both considerable magnetocaloric and magnetovolume effects can be also expected during the MT of these Fe3x alloys (x=0.4 and 0.6). In the remaining Fe1x and Fe2x alloys, the Fe doping disfavors the MT and also improves their brittleness. The structural preference of these cubic alloys and also their stability relative to the tetragonal martensite can be mainly attributed to the number of their minority density of states at the Fermi level: the smaller they are, the more stable their system tends to be.

Elastic Properties of B2-NiAl with W addition: A first-principles study

The effect of tungsten alloying on the elastic properties of B2-NiAl at low-temperature and high-temperature distribution of W atoms on sublattices. By means of the exact muffin-tin orbitals method in conjunction with the coherent potential approximation, the constants C11,C12,C44, Young's modulus E, shear modulus G, Cauchy pressure values, G/B ratios are calculated. Using phenomenological criteria of the correlation between ductility and elastic properties of solution phases, it has been shown that the addition of tungsten could yield improved ductility for B2-NiAl in both types of alloys. It is established that with the high-temperature distribution of W atoms on the Al sublattice, there is a loss of mechanical stability and a decrease in mechanical properties with increasing W concentration. In alloys with a low-temperature distribution of tungsten atoms between Al and Ni sites a unique combination of properties occurs: in addition to the ductility enhancement, a simultaneous increase of the elastic constants C44 and C11 and C11, shear modulus G, Young's modulus E with increasing W content is observed. The differences in the behavior of elastic constants in alloys with different types of tungsten distribution on NiAl sublattices are analyzed by calculating the density of electronic states. Keywords: NiAl, alloying elements, tungsten, elastic properties, ductility, first-principles calculations.

Упругие свойства B2-NiAl с добавлением W: исследование из первых принципов

The effect of tungsten alloying on the elastic properties of B2 NiAl at low-temperature and high-temperature distribution of W atoms on sublattices. By means of the exact muffin-tin orbitals method in conjunction with the coherent potential approximation, the constants C11, C12, C44, Young's modulus E, shear modulus G, Cauchy pressure values, G/B ratios are calculated. Using phenomenological criteria of the correlation between ductility and elastic properties of solution phases, it has been shown that the addition of tungsten could yield improved ductility for B2 NiAl in both types of alloys. It is established that with the high-temperature distribution of W atoms on the Al sublattice, there is a loss of mechanical stability and a decrease in mechanical properties with increasing W concentration. In alloys with a low–temperature distribution of tungsten atoms between Al and Ni sites a unique combination of properties occurs: in addition to the ductility enhancement, a simultaneous increase of the elastic constants C44 and C11, shear modulus G, Young modulus E with increasing W content is observed. The differences in the behavior of elastic constants in alloys with different types of tungsten distribution on NiAl sublattices are analyzed by calculating the density of electronic states.

Plastic deformation behavior of Pd-based binary alloys: A first-principles study

The generalized stacking fault energy is a critical parameter for plastic deformation and phase transition behavior of alloys. Here, the generalized stacking fault energies of palladium-based binary alloys (Pd 1− x M x , M = Mo, W, Re, Ru, Os, Rh, Ir, Pt; x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) in face-centered cubic (fcc) phase are systematically investigated by combining the coherent potential approximation with the exact muffin-tin orbital method within the framework of density functional theory. Analysis of the plastic behavior of Pd 1− x M x reveals that Mo, W, Re, Ru, and Os alloying elements can promote twinning, which in turn can be used to strengthen Pd alloys. When alloying reaches up to 30 at.% Mo, 40 at.% W, or 40 at.% Re, phase transition from fcc to hexagonal compact packing and stacking faults are the primary deformation of Pd 1− x M x . Contrarily, Rh, Ir, and Pt significantly suppress the twinning ability, and full slip becomes the dominant deformation mechanism. Such distinct deformation behavior of Pd-based alloys is attributed to their electron redistribution upon alloying, owing to the d - d hybridization between alloy elements and Pd atoms. This study gives valuable insight into the phase stability and provides useful guide for the design of high-strength alloys. • Alloying rich Mo, W, and Re into Pd promotes the phase transition from fcc to hcp. • Alloying elements Mo, W, Re, Ru, and Os can promote twinning mechanism of Pd 1−x M x . • Rh, Ir, and Pt alloying with Pd would facilitate full slip deformation. • Deformation of Pd 1−x M x is related to d-d hybridization between alloy atoms and Pd.

Alloying and magnetic disordering effects on the thermodynamic properties and phase stability of Co2Cr(Ga, Si) and Co2Cr(Al, Si) Heusler alloys

Using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, the alloying and magnetic disordering effects on the thermodynamic properties and phase stability of the ferromagnetic L21- and D022-CoxCr78−xZ11Si11 (Z=Ga and Al, 46≤x≤62) alloys are systematically investigated. It is shown that at 0 K, with increasing x the D022 structure gets relatively more and more stable in the energy and stabilized instead in the two groups of alloys with x≥56 and 60, respectively. There, upon the martensitic transformation (MT) the bulk modulus gets a little larger than that of the austenite, and both significant magnetocaloric and magnetovolume effects could be also expected. The tetragonal shear elastic constant (C′=(C11−C12)/2) of the L21 phase decreases whereas that (Cs=C11+C12+2C33−4C13) of the D022 phase increases with the Co addition, mechanically favoring the relative stability of the more ductile D022 martensite as well. The magnetic excitations decrease the electronic total energy but increase the phonon vibrational free energy of the D022 phase relative to the L21 one. The two effects nevertheless almost offset each other at their Curie temperature. The reentrant MT (RMT) is then predicted without the magnetic excitations effect in the Z=Ga and Al alloys with 50≤x≤54 and 54≤x≤58, respectively, and their critical temperatures (TM) for the RMT decrease with increasing x, in line with the measured data of the Z=Ga alloys. With the Co addition, the increase of the relative stability of their D022 phase is finally confirmed maybe originating from the increase of the Co 3d minority DOS around the Fermi level in their L21 phase.

First-principles calculations of the cleavage energy in random solid solutions: A case study for TiZrNbHf high-entropy alloy

The {100} and (110) cleavage energies of body-centered cubic TiZrNbHf high-entropy alloy are calculated using two alloy models: special quasi-random structures (SQSs) and the coherent potential approximation (CPA). The projector augmented wave method, as implemented in the Vienna ab initio simulation package (VASP), in combination with SQSs is adopted to evaluate the impact of local lattice distortions, whereas the exact muffin-tin orbitals (EMTO) method is used in combination with both SQSs and CPA to study the effect of chemical disorder using rigid underlying lattices. The variations of the cleavage energy as a function of surface chemistry and structure from the EMTO and VASP calculations are consistent with each other. Furthermore, the cleavage energies from CPA are in good agreement with those from SQSs, confirming that an averaged supercell approach reproduces well the mean-field CPA results. The alloy’s cleavage energies estimated by the rule of mixtures compare well with those from the direct calculations, and the surface chemistry dependence of the cleavage energies is mainly controlled by the number of Nb atoms in the surface terminal layers owing to the large cleavage energy of Nb metal.

Alloying and magnetic disordering effects on phase stability of Co2 Y Ga (Y = Cr, V, and Ni) alloys: A first-principles study

The alloying and magnetic disordering effects on site occupation, elastic property, and phase stability of Co2 YGa (Y = Cr, V, and Ni) shape memory alloys are systematically investigated using the first-principles exact muffin-tin orbitals method. It is shown that with the increasing magnetic disordering degree y, their tetragonal shear elastic constant C′ (i.e., (C 11 – C 12)/2) of the L21 phase decreases whereas the elastic anisotropy A increases, and upon tetragonal distortions the cubic phase gets more and more unstable. Co2CrGa and Co2VGa alloys with y ≥ 0.2 thus can show the martensitic transformation (MT) from L21 to D022 as well as Co2NiGa. In off-stoichiometric alloys, the site preference is controlled by both the alloying and magnetic effects. At the ferromagnetism state, the excessive Ga atoms always tend to take the Y sublattices, whereas the excessive Co atom favor the Y sites when Y = Cr, and the excessive Y atoms prefer the Co sites when Y = Ni. The Ga-deficient Y = V alloys can also occur the MT at the ferromagnetism state by means of Co or V doping, and the MT temperature T M should increase with their addition. In the corresponding ferromagnetism Y = Cr alloys, nevertheless, with Co or Cr substituting for Ga, the reentrant MT (RMT) from D022 to L21 is promoted and then T M for the RMT should decrease. The alloying effect on the MT of these alloys is finally well explained by means of the Jahn–Teller effect at the paramagnetic state. At the ferromagnetism state, it may originate from the competition between the austenite and martensite about their strength of the covalent banding between Co and Ga as well as Y and Ga.

Alloying and magnetic disordering effects on the martensitic transformation and elastic property of Co2VGa Heusler alloy: A first-principles study

Using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, the alloying and magnetic disordering effects on the phase stability and elastic property of L21- and D022-Co2VGa Heusler alloy are systematically investigated. It is shown that at the ground ferromagnetic (FM) state, Co2VGa alloy possesses the L21 structure and correspondingly, its shear modulus, Young modulus, and Debye temperature of the phase are all larger than those of the D022 phase. When the FM state transiting to the paramagnetic (PM) one, both C′(=(C11-C12)/2) and C44 of the L21 phase decrease whereas the elastic anisotropy increases, and they do so as well with increasing the number of valence electrons per atom (e/a) in the off-stoichiometric ternary and doped quarternary alloys with the FM ordering. As a result, at 0 K the magnetic disordered Co2VGa alloy with the disordering degree (y) larger than 0.2 can show the martensitic transformation (MT) from L21 to D022, and the MT is also obtained in the FM Co2V(Ga1-xZx) alloys with Z = Co (x⩾0.2), V and Ge (x⩾0.4), Si (x⩾0.5), and Sb (x⩾0.3). Accompanying the MT, their volume tends to decrease, and these L21 alloys possessing a bigger volume than those with the same e/a ratios are also relatively more prone to the MT. In the Z = V alloys, both greater magnetocaloric and magnetostrain effects may be expected during the MT as well. Both the minority Co d and V d states around the Fermi level should be responsible for the composition and magnetic ordering dependence of the phase stability of Co2VGa alloy.

Alloying effect on the order\u2013disorder transformation in tetragonal FeNi

Tetragonal ({hbox{L1}}_{0}) FeNi is a promising material for high-performance rare-earth-free permanent magnets. Pure tetragonal FeNi is very difficult to synthesize due to its low chemical order–disorder transition temperature (approx {593} K), and thus one must consider alternative non-equilibrium processing routes and alloy design strategies that make the formation of tetragonal FeNi feasible. In this paper, we investigate by density functional theory as implemented in the exact muffin-tin orbitals method whether alloying FeNi with a suitable element can have a positive impact on the phase formation and ordering properties while largely maintaining its attractive intrinsic magnetic properties. We find that small amount of non-magnetic (Al and Ti) or magnetic (Cr and Co) elements increase the order–disorder transition temperature. Adding Mo to the Co-doped system further enhances the ordering temperature while the Curie temperature is decreased only by a few degrees. Our results show that alloying is a viable route to stabilizing the ordered tetragonal phase of FeNi.

Impacts of atomic and magnetic configurations on the phase stability of Fe–Pd shape memory alloys: A first-principles study

The effects of local atomic and magnetic configurations on the phase stability and elastic property of the face-centered cubic (fcc) and two body-centered tetragonal [face-centered tetragonal (fctI) and fctII, with 0.9&amp;lt;c/a&amp;lt;1 and 0.71&amp;lt;c/a&amp;lt;0.9, respectively, in the fct unit cell] phases of Fe1−xPdx (0.28≤x≤0.34) shape memory alloys are systematically investigated by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. It is shown that, considering four types of atomic configurations in a fcc unit cell, the two with one random sublattice are both preferable in each x below 300 K. When T=300 K, the one with three random sublattices also changes to be stabilized for x≤0.30, whereas that with four random sublattices becomes stable in most of these alloys until T≥600K. Upon tetragonal distortions, in these fully disordered alloys, both the fctI and fctII phases are unstable. The fctI phase is found for 0.29≤x≤0.33, having only the configuration with one random sublattice on the same layer with the Pd site in the unit cell, whereas the fctII phase is obtained for x≤0.30, possessing all the configurations with one, two, and three random sublattices. These results representing the phase diagram of these alloys, their determined equilibrium lattice parameters, and elastic constants of the three phases at 0 K are in line with the experimental and theoretical data, and their estimated structural (TM) and magnetic (TC) transition temperatures are also close to the experimental data. Adding 4% magnetic disorder in Fe0.70Pd0.30, the fctII structure is effectively prevented, whereas the thermoelastic martensitic transformation of fcc–fctI can still be retained at 0 K.

Magnetic Phase Transition, Elastic and Thermodynamic Properties of L12-(Ni,Cu)3(Al,Fe,Cr) in 3d High-Entropy Alloys

The phase stability and elastic properties of paramagnetic (PM), ferromagnetic (FM) and antiferromagnetic (AFM) phases in L12-(Ni,Cu)3(Al,Fe,Cr) alloy are first investigated using the exact muffin-tin orbitals (EMTO) method in combination with the coherent potential approximation (CPA). The result shows the AFM structure phase of the three is the most stable in the ground state. Calculated elastic constants show that all the phases are mechanically stable, and have uncovered that L12-(Ni,Cu)3(Al,Fe,Cr) can achieve good strength and ductility simultaneously. Then, crucial thermal properties are described satisfactorily using the Debye–Grüneisen model, showing heat capacity, Gibbs free energy G, the competitive contribution of entropy −TS and enthalpy H exhibiting significant temperature dependences. Moreover, the magnetic phase transition thermodynamics was studied, which suggests that −TS has a primary contribution to Gibbs free energy and may play a key role in the phase transition. The present results can benefit the understanding of the mechanical, thermodynamic and magnetic properties of the L12 structure phase in 3d high-entropy alloys.

Exact muffin-tin orbital based fully relativistic simulation of device materials: Electronic charge and spin current

We report the implementation of the fully relativistic exact muffin-tin orbital (EMTO) method for both first-principles electronic structure and quantum transport simulation of magnetic and nonmagnetic device materials. We consider a device-material system containing the inevitable atomic disorders in contact with different electrode materials. The Kohn-Sham Dirac equations for both cases with and without spin polarization are self-consistently solved for the central device-material system with the Green's function method. The fully relativistic charge-current density, conventional Pauli spin current density, and transmission coefficient are formulated with the nonequilibrium Green's function technique. To treat the influence of disordered defects/impurities, we combine the nonequilibrium Green's function in the Keldysh space with the coherent potential approximation, and account for the multiple disorder scattering by vertex corrections to a two-Green's-function correlator to calculate the disorder-averaged charge and spin current density. As a demonstration of the present implementation, we calculate the electronic structure of the bulk Pt, Co, and HgTe and Rashba-type surface states of Au and Ag/Ag2Bi1 alloy surfaces. We find that the EMTO electronic structures of all the calculated systems agree well with the results of the projector-augmented wave method. The electronic charge and spin transport implementations are tested with perfect and disordered Cu/Co/Pt/Cu junctions. The important effects of interface and atomic disorders are illustrated for the spin transport in the presence of relativistic effects. The implementation of the fully relativistic EMTO-based device-material simulation provides an important tool for analyzing both the charge and spin transport through nanostructures and materials, significantly extending the capability of first-principles material design for spintronic device applications.

Effect of alloying elements on lattice misfit and elasticities of Ni-based single crystal superalloys by first-principle calculations

The site occupancy, lattice misfit and elastic modulus of Ni-based single crystal superalloys are investigated by combining the first principles exact muffin-tin orbital method and coherent-potential approximation. The site preference of alloying elements in γ′-Ni3Al can be classified into four types: Co, Fe, Ru and Ir occupy Ni site or Cr, Mo, Re, Ti, V occupy Al anti-site (namely alloying elements occupy Al site while the removed Al occupy Ni site). Ti and V are the alloying elements which stabilize the γ′-Ni3Al. The lattice misfit and the difference of elastic properties between γ and γ′ phases are the causes of γ′ rafting, while the alloying elements will improve the differences. The effects of 1 at. % ~5 at. % alloying elements on lattice constant and misfit are studied, because of biggish atomic radius, Ir, Mo, Ti, Re and Ru increase the lattice constant of γ/γ′ phase much faster, and the alloying elements have some impacts on the lattice misfit of γ/γ′ phase. Re is the most remarkable alloying element which improves the elastic modulus of Ni-based superalloys.