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The electronic structure and thermoelectric transport properties of AgGaTe2 are studied by density functional theory and Boltzmann transport theory. Owing to the spin–orbit coupling, the electronic band structure behaves in an obvious decoupling effect of the degenerate band. The enhancement of the power factor of AgGaTe2 through carrier concentration tuning is predicted.

We present a systematic and comparative study of the electronic properties of CeX monochalcogenides, The density of state (DOS) and electronic band structure of CeX (X=S, Se, Te) have been calculated using the full-potential linearized augmented plane-wave (FP-LAPW) + local orbital (lo) method based on the density functional theory (DFT), which is implemented in WIEN2k code. The trends in the high pressure behavior of these systems are discussed. Four approximations for the exchange-correlation functional have been used, the GGA's of Perdew-Burke-Ernzherhof. (PBE08) , Engel-Vosko (EV93), a modified version of the exchange potential proposed by Becke and Johnson (MBJ), and LDA+U is used to calculate the band gaps at different pressures. All methods allow for a description of the Ce f electrons as either localized or delocalized, it is found that the underestimations of the bandgap by means of LDA-GGA and Engel-Vosko are considerably improved by using the modified Becke-Johnson (MBJ) potential for all compounds in the series, On the other hand, LDA+U, method gives good results for the lighter chalcogenides, but it fails to give good results for the heavier cerium monochalcogenides.

In this work, we present a density-functional theory study of structural, electronic and optical properties of BAs, BN binary compounds and their ternary BN x As 1− x solid solutions. The calculations are done by using the all-electron full potential linear augmented plane-wave method (FP-LAPW) as employed in WIEN2k code. For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The electronic band structure of these compounds have been calculated by using the above two approximations. We have also investigated in this article the density of state and the optical properties such as the dielectric function and the refractive index of BAs, BN and BN 0.25 As 0.75 compounds by using the above method. The results obtained for structural and electronic properties are compared with experimental data and other computational work. It has been found that the energy bands with all these approximations are similar except the band gap values. It has also been found that our results with LDA and GGA are in good agreement with other computational work wherever these are available.

We calculated the electronic structure and thermoelectric properties of the Ge-doped quaternary clathrate Ba-Ga-Sn-Ge. The electronic structure was calculated by using the WIEN2k code, which is based on the full-potential augmented plane-wave method. Using this method, we calculated the total energies for several Ge configurations to determine the positions of Ge atoms in the unit cell. The calculated Ge positions were in good agreement with the experimental results. Based on the resulting Ge positions, the band structure and thermoelectric properties of the Ba-Ga-Sn-Ge clathrates were calculated.

In present paper, the structural, elastic, thermal, electronic, optical properties at ambient and high-pressure study of Ag 2 O are performed using the full-potential linearized augmented plane wave (FP-LAPW) method within the framework of Density functional theory (DFT) as implemented in Wien2k Code. We have used the local density approximation (LDA), Generalized Gradient approximation (GGA) and Engel–Vosko generalized gradient approximation (EV–GGA) for calculating structural properties at 0.0–20.0 GPa pressure. The lattice constant obtained at 0.0 GPa using GGA method, is in good agreement with available experimental results. Decrease in lattice constant is observed with increase in pressure from 0.0 to 20.0 GPa. The electronic, optical and band structure calculations are also carried out using modified Becke–Johnson exchange correlation potential plus generalized gradient approximation (mBJ–GGA). At zero pressure, the calculated band gap using mBJ potential is found to be narrow, direct and comparatively better than calculated through LDA, GGA and EV–GGA. Also, the band gap increases with increase in pressure from 0.0 to 20.0 GPa. From elastic calculations, it is noted that Ag 2 O is elastically stable and have ductile nature. Moreover, it is revealed that Ag 2 O is suitable for optoelectronic devices.

Gallium Arsenide (GaAs) because of having unique characteristics like direct band gap, higher electron mobility and saturated electron velocity etcetera, has wide applications specifically in optoelectronic devices. In this research work we present a comprehensive density functional theory (DFT) based first principles study of optical properties of GaAs. Exchange correlation functional (XC) play a key role in the DFT investigations. A comparative study of the optical properties is presented based upon local density approximation (LDA) by Perdew and wang, Perdew-Burke-Ernzerhof parameterized generalized gradient approximation (GGA-PBE), Wu-Cohen parameterized GGA (GGA-WC) and Engel and Vosko proposed GGA (GGA-EV). Computations in this study have been performed by full potential (FP) linearized augmented plane wave (LAPW) plus local orbitals (lo) approach designed within DFT as realized in the computational code WIEN2k. Our investigations, for the optical properties of GaAs with mentioned XC potentials, cover detailed analysis of dielectric functions, absorption coefficient α (ω), energy loss functions, reflectivity R(ω), refractive index n (ω) and extinction coefficient k (ω). The analysis shows that the optical parameters calculated with GGA-PBE are comparatively reasonable and closer to the experimental results. Keywords: Density functional theory, local density approximation, gradient and other corrections, APW calculations, Dielectric function, absorption and reflection spectra PACS: 71.15.Mb, 71.15.Ap, 77.22.Ch, 78.40.Pg

Nuclear magnetic resonance (NMR) parameters of 11B in borates and borosilicates, unlike those of many other nuclei such as 29Si and 27Al, vary only in limited ranges for a given polyhedral geometry, but mechanisms for such insensitivity to local structural environments remain poorly understood. In this contribution, ulexite and probertite, with the ([B5O6(OH)6]3−) pentaborate polyanion as the fundamental building block, have been investigated in detail by ab initio theoretical calculations of the density of states (DOS) as implemented in WIEN2k, including optimization of the structures and determination of contributions to the magnetic shielding at each of the five distinct B sites. Calculated 11B NMR parameters of these two pentaborates are compared with high-precision experimental data obtained at high (14 T) and ultrahigh (21 T) fields. Optimized structures using the linearized augmented plane-wave method with additional radial basis functions in the form of local orbitals (i.e., LAPW+lo) not only yield more accurate electric field gradients (EFG) at the distinct three- and fourfold-coordinated B sites (i.e., [BO3] or [3]B and [BO4] or [4]B) but also improve the calculated 11B magnetic shielding. In particular, the magnetic shielding variation trends among the B sites in ulexite and probertite are determined mainly by the valence states and especially by the local p orbitals of B and its nearest-neighbor O atoms. Calculations with the water molecules removed or K+ substituting for Na+ in the structures show that the next-nearest-neighbor cations and water molecules have negligible effects. Theoretical calculations also reveal that the systematic differences in shielding between [3]B and [4]B are caused by multiple factors such as the occupancies and imbalance in the sp hybrid orbitals between B and its nearest-neighbor O atoms.

An ab initio full-potential linear augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA), as implement in Wien2k code, has been used to study the structural, electronic and optical properties of the fluoropervskite SrXF 3 (X = Li, Na, K and Rb) compounds. The calculated lattice constant and bulk modulus are in agreement with previous calculations. The calculated band structures show a direct band-gap ( Γ – Γ ). The contribution of the different bands is analyzed from the total and partial density of states curves. The dielectric function, refractive index and extinction coefficient are calculated. The origin of some of the peaks in the optical spectra is discussed in terms of the calculated electronic structure. The values of static dielectric constant e 1 (0) is found to be increasing with a decrease in the energy band-gap.

The theoretical calculations on structural, electronic, half-metallic and elastic properties of both VZrAs, VZrSb half-Heusler compounds and Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) diluted magnetic semiconductors (DMSs) have been investigated using WIEN2k. In Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs, the ferromagnetic phases are more stable than non-magnetic and antiferromagnetic phases. In VZr(As, Sb) compounds, the ferromagnetic (FM) phases in Type II structure are more stable energetically. The spin-up electrons of both half-Heusler compounds have semiconducting nature with 0.643 and 0.799 eV energy gaps while spin-down electrons of Al0.875Fe0.125As, Al0.9375Fe0.0625As and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs have semiconducting feature. The mechanically stability conditions are provided by all compounds except VZrAs half-Heusler compound. Therefore, VZrSb, Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) diluted magnetic semiconductors (DMS) are mechanically stable against the deformation. The VZrAs compound can be deformed in the experimental process since it does not provide the C-11 > C-12 mechanical stability condition. According to conditions of the ductility or brittleness of polycrystalline material, both VZrAs and VZrSb half-metal compounds are ductile materials while Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs are brittle. Finally, VZr(As, Sb), Al1-xCoxAs (x = 0.0625, 0.125, 0.25) and Al1-xFexAs (x = 0.0625, 0.125) compounds were obtained true half-metal ferromagnetic materials (HMF) within 4.00, 2.00 and 5.00 mu(B)/f.u. (C) 2019 Elsevier B.V. All rights reserved.

A systematic investigation on structural, electronic, magnetic and optical properties of Zn(1−x)AxS (A = Cr/Mn/Fe) are performed using first principles calculations within the frame work of spin polarized density functional theory (SP-DFT) as implemented in WIEN2k. The electronic, magnetic and optical properties are performed using the local spin density approximation (LSDA) coupled with modified Becke Johnson (mBJ) potential. The present results show that Zn(1−x)MnxS systems exhibit semiconducting behaviour whereas a half-metallic character is shown by both Zn(1−x)CrxS and Zn(1−x)FexS systems. Although undoped ZnS is a non-magnetic semiconductor, the calculated spin polarized density of states of Cr2+:ZnS and Fe2+:ZnS show 100% spin polarization at Fermi energy, EF. The optical properties, including the real and imaginary part of dielectric function, reflectivity, refractive index, absorption co-efficient, electron energy loss function and optical conductivity of undoped ZnS and Zn(1−x)AxS (A = Cr/Mn/Fe) systems are calculated using mBJ potential. The substitution of Cr and Fe in ZnS not only influences the position of absorption peaks of parent semiconductor in the UV region, but also leads to the formation of new narrow peaks in the visible and IR regions. A considerable red shift in the absorption peak due to the substitution of Fe and Cr shows a good agreement with the previous theoretical results. These outcomes imply that Zn(1−x)AxS (A = Cr/Fe) systems cover the spectral range from IR to near UV and seem to be the promising candidates for optoelectronic and spintronic applications.

The cubic perovskite structures have enlarged the potential for their wide applications for the purpose of hydrogen storage. The present research work aims at undergoing the theoretical study of perovskite type hydrides LiXH3 (X = Ba, Sr and Cs). The study includes the investigation of structural, electronic and thermal and thermodynamic properties using full potential linearized augmented plane wave (FP-LAPW) method under the frame work of Density Functional Theory (DFT) by employing WIEN2k code. The calculated parameters for structural, electronic and thermal properties are in good agreement with the literature work. Results reveal that all the compounds have indirect band gaps of values of 1.48eV, 1.35eV and 1.73eV for LiBaH3, LiCsH3 and LiSrH3, respectively and these calculated band gaps are in good agreement with other theoretical work. In addition, the thermoelectric properties calculated by solving the Boltzmann transport equation reveal that LiBaH3 possesses superior electrical properties in comparison with the LiSrH3 and LiCsH3. Using density functional perturbation theory, we have also calculated the phonon dispersion curves and phonon density of states with the help of the CASTEP code. Various thermo-dynamical properties, such as heat capacity, Debye temperature, Enthalpy, Entropy and free energy have been calculated with the help of thermodynamic functions by using phonon density of states and results reveal that LiBaH3 is more stable as compared to LiSrH3. Moreover, results also exhibit that LiCsH3 is an unstable compound in the cubic phase.

Current study is first ever computational study to predict optical and electronic properties of Na doped CdS system. A good comparison among optical properties of pure CdS and its doping with various Na concentrations (3.12%, 6.25%, 9.37%) is shown in our study. Cd atoms are substituted with Na atoms and a change in optical properties is studied while size of supercell ( 1 × 2 × 2 ) is kept constant for all cases. In comparison to absorption of pure CdS, the absorption shows blueshift upon increase in Na concentrations and refractive index first increase and then decreases for higher Na concentration (9.37%). Absorption increases in the visible region while for UV region it somehow shows oscillatory trend. Entire study has been executed using Wien2k code by employing PBE-GGA approximation and the manuscript is furnished with detailed discussions regarding plausible applications of CdS:Na system which highlight future directions of this material. Moreover, insight into optical properties of CdS:Na system shows surprising results which appeal candidacy of this material to be potentially used for device fabrication in the field of optoelectronics, non-linear optics, dielectrical electronics, functional microelectronics, electrostatic capacitors and piezoelectric transducers.

Employing the density function theory (DFT) within the full potential linearized augmented plane wave (FP-LAPW) method implemented in the Wien2k package, the structural and electronic properties of the ternary Al1-xBxAs alloys with their bordered binary compounds AlAs and BAs have been investigated. In order to get the difference between the generalized gradient approximations (GGA) proposed to the exchange and correlation potential, we have interested in this work for the Wu-Cohen (WC-GGA), Perdew-Burke-Ernzerhof (PBE-GGA) and Perdew et al (PBEsol-GGA) schemes which are used to calculate the structural, electronic and optical properties of materials. Furthermore, the modified Becke Johnson potential of Tran and Blaha (TB-mBJ) method is also used to determinate accurate band gap energies of the interested materials. The structural properties such as the lattice constant, bulk modulus and the pressure derivative are computed from the total energy given in the cubic structure for the ternary alloy Al1-xBxAs at the compositions (x = 0.0, 0.25, 0.50, 0.75, 1.0). The electronic band structures, the densities of state (DOS) as well as the optical properties for the same compositions are also computed. The obtained results compared well with the experimental data and previous theoretical results. Moreover, in this study we have also invoking the thermodynamic and the elastic properties of materials in the goal to understanding the behavior of the alloys under the effect of temperature and the pressure.

The optoelectronic properties of InxGa1−x(As/Sb) are analyzed using density functional theory by employing a modified potential scheme of Trans and Blaha as developed in WIEN2k code. The indium doping in GaAs and GaSb tune the band gap from 1.56 to 0.43 eV and 0.82 to 0.30 eV, respectively, which highlights their significance for solar cell related applications. The optical characteristics are assessed by studying the dielectric constant, refraction, absorption, optical conductivity and optical loss of light energy. The static dielectric constant related to the optical band gap through Penn's model and with static refractive index = n2(0) increase consistently between the calculated results. The maximum absorption and small optical loss factor for visible to near UV regions can enhance the optical efficiency for solar cell and optoelectronic applications. Moreover, higher optical conductivity within 3.5–4.5 eV allows forward current, which is attractive for practical applications.

Density functional theory (DFT) within Wien2k code is utilized to compute the mechanical, thermal, electronic, magnetic and thermoelectric properties of the cubic spinel CoV2O4. The ground state lattice constant of CoV2O4 alloy agrees with previous literature. The calculated elastic constants of CoV2O4 predict that the present alloy is anisotropic, elastically stable and brittle. Beneficial acoustical applications are expected for the present alloy due to its high calculated Debye temperature and average sound velocities values. The longitudinal and transverse sound velocities modes of vibrations are found maximum along [110] directions compared to [100] and [111] directions. The calculated DOS and band structure show that CoV2O4 is electronically stable. The present alloy possesses a total magnetic moment of 12.0 [Formula: see text] and is classified as a half-metallic ferromagnet. CoV2O4 shows [Formula: see text]-type behavior and favors holes as charge carriers. The present alloy owns beneficial thermoelectric properties and can be used in thermoelectric applications.

Equilibrium Stannite structure (SS), Kesterite structure (KS) and Diamond structure of Ag2MnSnS4 are investigated by using density functional theory (DFT) within Wien2k code based on the generalized gradient approximation (GGA) and the modified Becke-Johnson exchange potential (mBJ). P-type conductivity is found for Kesterite and Stannite phases while n-type semiconductor is found for Diamond phase. For all structures, Ag2MnSnS4 exhibits a semiconductor characteristic with a direct band gap of 1.24 eV,1.4eV and 1.7eV for Stannite, Kesterite and diamond structure respectively. Additionally, the calculations of the electronic and optical properties of the compounds display a considerable wavelength absorption in the ultraviolet range. Furthermore, the findings obtained for Ag2MnSnS4 have later been subjected to a comparative study, whereby the theoretical and experimental results of Cu2ZnSnS4 (CZTS) belonging to the same chalcogenide family, have been adopted.

The theoretical calculations on structural, half-metallic and elastic properties of FeZrX (X = P, As, Sb and Bi) half-Heusler compounds were investigated using WIEN2k code. In all compounds, the ferromagnetic (FM) phases in Type II structure are more stable energetically than non-magnetic (NM) phases. The spin-up electrons of all half-Heusler compounds have semiconducting nature with energy gaps while spin-down electrons have metallic behavior. FeZrM (M = III, IV and VIAgroup elements) compounds have also been investigated, but these compounds have metallic properties, whereas FeZrP, FeZrAs, FeZrSb and FeZrBi compounds have half-metal nature. According to calculatedCij elastic constants, FeZrX (X = P, As, Sb and Bi) half-Heusler compounds are elastically stable and these compounds are ductile materials. Finally, FeZrX (X = P, As, Sb and Bi) half-Heusler compounds were obtained true half-metal ferromagnetic materials (HMF) within 1.00 mu(B)/f.u.

First-principles total energy calculations have been performed using the full potential linearised augmented plane wave (FP-LAPW) method as implemented in the WIEN2k code based on the densi...

The electronic, mechanical and optical properties of PbZrO3 and PbHfO3 have been studied by density functional theory (DFT) based modified Becke and Johnson (mBJ) potential as implemented in Wien2k code. The structural and mechanical stabilities of studied perovskites in cubic phase are confirmed by tolerance factor (0.97 for PZO and 1.0 for PHO), enthalpy of formation, specific heat capacity and positive values of elastic constants (Born mechanical stability condition). The lattice constant and bulk modulus of the studied compounds are inversely related. The band gap of PHO lies in the visible region while band gap of PZO lies in the ultraviolet region. The ductile nature has been assured by the Pugh's (B/G > 1.75) and Poisson (υ > 0.26) ratios. The optical behavior of the studied compounds has been explored in terms of dispersion, polarization, absorption, reflection, conduction and optical energy loss. The maximum absorption of light in the visible to near ultraviolet region, minimum reflection and optical loss that makes the studied materials most suitable for solar cell and optoelectronic devices.

In this study, thermo-elastic and lattice dynamic properties of XMgAl (X = Li, Na) half-Heusler compounds are investigated using density functional theory implemented in WIEN2k and Quantum ESPRESSO codes. Generalized gradient approximation (GGA) as an exchange correlation function has been used in Kohn–Sham equations. Firstly, the structure of these Heusler compounds is optimized and then these optimized parameters are used to find three elastic constants [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text] type structures. Three elastic constants are then used to determine different elastic moduli like bulk modulus, shear modulus, Young’s modulus and other mechanical parameters like Pugh’s ratio, Poisson’s ratio, anisotropic ratio, sound velocities, Debye temperature and melting temperature. On behalf of these mechanical parameters, the brittle/ductile nature and isotropic/anisotropic behavior of the materials has been studied. Different regions of vibrational modes in the materials are also discussed on behalf of Debye temperature calculations. The vibrational properties of the half-Heusler compounds are computed using Martins–Troullier pseudo potentials implemented in Quantum ESPRESSO. The phonon dispersion curves and phonon density of states in first Brillion zone are obtained and discussed. Reststrahlen band of LiMgAl is found greater than NaMgAl.

We present comparative calculations of the electronic structure of Cd and Zn based group II–VI compounds and their heterostructures based on the density functional and tight binding theories. The first principles density functional theory (DFT) uses the modified Becke–Johnson exchange potential with LDA correlation potential (MBJLDA) and the semi-empirical tight binding theory uses the first nearest neighbor (NN) s p 3 d 5 and second nearest neighbor (2NN) s p 3 s ⁎ basis with spin–orbit coupling of II cation (Cd, Zn) and VI anion (S, Se, Te) atoms for calculating the electronic structure of Cd and Zn based II–VI compounds and their heterostructures. The results of DFT with MBJLDA functional and NN s p 3 d 5 and 2NN s p 3 s ⁎ TB models are found to be in excellent agreement with measured band gaps of CdX and ZnX (X=S, Se, Te) based group II–VI compounds and their CdZnS/CdS, CdSTe/CdTe and ZnSSe/ZnSe heterostructures. We conclude that the NN s p 3 d 5 TB model gives much more physical insight than the (2NN) s p 3 s ⁎ TB model, making use of the fictitious s* state unnecessary.

Electron energy loss near edge structure spectra of the N-K edge of InxAl1-xN.Effect of In in the electronic structure and the bonding environment of N in InAlN.Effect of oxygen concentration on the bonding environment of N in AlN. We present a systematic computational study of electron energy loss near edge structure (ELNES) spectra of the N-K edge of InxAl1-xN with various indium contents. Density functional theory calculations are implemented by means of WIEN2k code. Supercell size as well as core-hole effects are investigated in order to establish the optimum parameters. Based on the known electronic structure of bulk wurtzite AlN, the fine structure of N-K ionization edge is investigated in order to study the effect of Indium in the electronic structure and the bonding environment of Nitrogen in InAlN alloys. The unintentional oxygen contamination in MOVPE In0.24Al0.76N and the variation of the indium content on defected areas of the structure are investigated.

We have investigated the electronic structure and half-metallic ferromagnetism in zinc blende phase of Be1−x V x M (M=S, Se, Te) at concentration x=0.125 by employing a first-principles calculations within the framework of density functional theory (DFT) based on the linearized augmented plane wave method (FP-LAPW), as implanted in the WIEN2k code with generalized gradient approximation functional proposed by Wu and Cohen (WC-GGA). The electronic properties exhibit half-metallic behavior. So the density of states shows the hybridization between the p (S, Se, Te) and 3d (V) states that creates the antibonding states in the gap, which stabilizes the ferromagnetic ground state associated with the double-exchange mechanism, whereas the spin polarized band structures depict half-metallic gap that increases from Be0.875V0.125S to Be0.875V0.125Se to Be0.875V0.125Te. These compounds are robust half-metallic ferromagnets with spin polarization of 100 % and predicted to be potential candidates for spin injection applications in spintronic devices. Therefore, our predictions require an experimental confirmation in the future.

In current research, we perform a computational study to calculate optical properties of Al doped CdS system for 1 × 1 × 2, 2 × 2 × 1, 2 × 2 × 2 supercell configurations and for DFT + U (1 × 2 × 2). Cd atoms are substituted with Al atoms and the result for optical properties shows significant changes in the case of 2 × 2 × 1 supercell configuration. This study has been executed with PBE-GGA and GGA + U approaches, used in Wien2K code employed within the framework of DFT. In comparison to 1 × 1 × 2 supercell configuration, optical absorption for 2 × 2 × 1 supercell configuration and DFT + U shows blueshift while for 2 × 2 × 2 redshift is observed. Study explore that optical properties are enhanced and absorption increases in visible region. Hence, Al doping into host CdS lattice suggest that opto-electrical properties are enhanced which advocate candidacy of this material for nanotechnology and optoelectronic devices.

The half-metallic and elastic properties of Mn2IrAl full-Heusler compound was investigated using WIEN2k code. The ferromagnetic (FM) states were compared non-magnetic (NM) states in Hg2CuTi and Cu2MnAl structures for determined which phase was the most stable. The FM phase in Hg2CuTi structure was observed more stable energetically. The computed results showed that the spin-up (majority) electrons of Mn2IrAl compound had metallic feature while spin-down (minority) electrons had semiconduction behavior with an energy gap of 0.43 eV. According to calculated C-ij elastic constants, Mn2IrAl compound was elastically stable as it provides stability conditions and it was a ductile material. Finally, Mn2IrAl compound was found true half-metallic ferromagnet within 2 mu(B)/f.u.

In this paper, we presented an ab-initio study of the structural, electronic and optical properties of the binary compound of indium phosphide (InP). This material is widely used in the field of optoelectronics and microelectronics fast. Our calculations were made by the method of augmented plane wave (FP-LAPW), based on the density functional theory (DFT) and implemented in the calculation code Wien2k. This calculus of the electronic band, structure and optical properties were performed using local-density approximation (LDA), generalized gradient approximation (GGA), and a combination of modified Becke—Johnson exchange potential plus LDA and GGA (mBJ + LDA/GGA) for exchange–correlation potential. We find in our calculations, the usual trends, that the (GGA) unlike LDA overestimates the lattice parameter and underestimates the bulk modulus. The phase transitions for this material from structure B3 to structures Imm2, B8-1, B10 and B2 are possible under low pressures and The calculation of the density of state gives a detailed explanation of the contribution of the different orbitals.

The structural, electronic, and magnetic properties of MnAs crystal are studied. The WIEN2k code which uses a full-potential LAPW program based on density functional theory with GGA is used for the calculations. At first, the total energy of a MnAs crystal in different lattices is calculated and the corresponding - diagram is drawn for two different structures of MnAs. The effect of pressuring this crystal is determined. The calculations confirm that, MnAs has the NiAs-type structure at ambient pressure but transforms into the zinc-blend structure of a specific pressure value. Also, the electric field gradient (EFG) and hyperfine field (HFF) at the nuclear site of Mn and As are calculated. Finally, the effect of pressure on EFG and HFF is studied.

The electronic properties and the optical properties of wurtzite InN are studied by the first-principles calculations based on the density functional theory. The calculations are based on the Generalized-Gradient Approximation (GGA) and implemented in Plane Wave Self-Consist Field (PWSCF). The optical properties of InN are investigated by the pseudo-potential method with PBEsol-GGA within the WIEN2K program. Band structure, density of states and dielectric functions are calculated detailedly. The energy transitions are observed and compared existing data at critical points. Moreover the new peak in between the region 12 eV to 14 eV should be due to transitions from the In-5p states to the N-2s states.

The dielectric properties of V2O5 nanofibers, synthesized by the electrospinning method, are studied by analyzing the low-loss region of the electron energy loss spectroscopy (EELS) in a transmission electron microscope. A comparison of experimental EELS spectra and ab initio density-functional theory calculations (WIEN2k code) within the Generalized Gradient Approximation (GGA) is presented, having found an excellent agreement between them. Although the experimental EELS has been acquired for the nanoparticles composing the fibers, and numerical calculations were carried out for bulk material, agreement between experimental and calculated results shows that no difference exists between the electronic structure in calculated bulk material and the nanoparticles. Furthermore, our results from EELS confirm that we accomplished the expected crystalline phase. The origins of interband transitions are identified in the electronic band structure by calculating the partial imaginary part of the dielectric function and the partial density of states.

Core hole Binding energies Ab-initio calculations Ionization energies XPS experiments a b s t r a c t It is known that ionization potentials can be calculated in density-functional theory using Slater transition state technique. In this work a modified version of this technique is used to calculate binding energies for 31 metals. The technique to produce these energies involves ab-initio calculations performed using the FP-LAPW method, with the GGA approximation using the DFT formalism according to the implementation in the Wien2k code. In these calculations the occupation of the 1s states was reduced according to the fractional core hole as a function of Z, which is presented in this work. The theoretical K, L1, L2 and L3 binding energies were compared with Berkeley ionization energies and they show a considerable improvement compared to those calculated with the normal occupation of the 1s state.

The magneto-optical Kerr effect (MOKE) for both Heusler type alloys (AuMnSb and AuMnSn) were studied using the full-potential linearized augmented plane-wave (FP-LAPW) method, based on the density functional theory implemented in the WIEN2k code. The differences with previous calculations on the Kerr spectra have been found explicitly. At proper Lorentzian such asδ= 0.4 eV, the calculated Kerr angle of AuMnSn reaches its maxima +0.3° near 0.6 eV and-0.5° at 5.2 eV, respectively while the MOKE spectra of AuMnSb exhibit less prominent Peaks (+0.5° at 0.3 eV, -1.9° at 0.9 eV, -1.0° at 2.4 eV and-2.0° at 5.3 eV). The results on the spectra in this work showed quite a lot differences with all previous all-electron calculations. It is concluded that the contribution from Sb (or Sn) site to the magneto-optical kerr effect is quite crucial in Heuslar alloys.

The electronic and optical properties of $$\text{ Zn }_{1-\mathrm{x}}\text{ M }_\mathrm{x}\text{ Te }$$ with (M = Cr, Mn, Ti) have been investigated, within generalized gradient approximation (GGA) using the full potential linear augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. This work presents detailed information about optical properties like absorbance, refractive index and reflectivity. The result of this study shows that doped ZnTe material with Ti, Cr and Mn shift the absorption spectrum and reflection to the infrared spectral domain or to the ultra violet region, depending on the nature of the dopant. Dielectric functions for different compositional alloys are calculated for 16-atom cubic supercell structure. The calculated band gaps are fitted with a linear equation: ( $$\upalpha \text{ h }\upnu )^{2} = \text{ A }(\text{ h }\upnu -\text{ Eg }$$ ). For all types of doping the position of critical points (CP’s) $$\text{ E }_{0}, \text{ E }_{1}$$ and $$\text{ E }_{2}$$ show good agreement with the experimental data.

Using density functional theory (DFT) calculations, we investigated the electronic and magnetic properties of the Heusler compounds Co2TGe (T = Sc, Ti, V, Cr, Mn, Fe). Among the systems under investigation Co2CrGe and Co2MnGe have given 100% spin polarization at the Fermi energy (EF). Co2CrGe is the most stable half-metallic ferromagnets (HMFs) with an energy gap of 0.24 eV at the Fermi level (EF) in spin down channel. We have also found an increase in the total magnetic moments as T goes from Sc to Fe. The calculated magnetic moments for Co2CrGe and Co2MnGe are 3.999 µB and 5.00 µB respectively. Based on the local spin density approximation (LSDA) calculated results, we have predicted that the compounds Co2CrGe and Co2MnGe are HMFs. We have tried to study the HMFs in Co2ScGe, Co2TiGe, Co2VGe and Co2FeGe by using the local spin density approximation and Coulomb repulsion (U) (LSDA+U) when the simple generalized gradient approximation (GGA) or the LSDA fail.

The structural, electronic and bonding properties of ThCr 2 Si 2 -type compounds, namely, CaTM 2 Pn 2 (TM = Ni, Pd; Pn = P, As) with space group I4/mmm (139) are obtained under compression by means of Full Potential – Linearized Augmented Plane Wave (FP – LAPW) method as implemented in WIEN2K code. The optimized lattice parameter, the positional z -parameter, Fermi energy, Density of States (DOSs) at Fermi Level, electronic specific heat coefficient and the distance between Ni(Pd)–P(As) and P(As)–P(As) atoms at equilibrium lattice configuration and under compressions are reported. Electron density plots, band structure plots and DOS are illustrated and compared. Different bonding characteristics are noted and compared. Our work predicts the possible range of bond lengths for the occurrence of covalent bonding between the pnictogens in these compounds. High pressure band structure calculations reveal the possibility of Electronic Topological Transition (ETT) in these compounds.

We report a novel scheme for computing electronic excitation energies within the framework of density functional theory (DFT) based on a time-independent variational formulation of DFT. The excited state density functional is recast as a Kohn-Sham functional, which is further simplified by an adiabatic approximation of the exchange-correlation functional. Under the adiabatic approximation, the minimization of the excited state Kohn-Sham functional is shown to be equivalent to a ground state DFT computation augmented with orthogonality constraints with respect to the ground state Kohn-Sham determinant. An algorithm for the optimization of the energy subject to orthogonality constraints, which does not suffer from variational collapse, is described and implemented. A benchmark test set containing 28 organic molecules (Schreiber, M. J. Chem. Phys. 2008, 128, 134110) was used to assess the quality of the excitation energies obtained. Two novel approaches to spin-adapt the resulting excitation energies are discussed and found to provide results with error metrics similar to those of time-dependent DFT. Similarities and differences with respect to other time-independent DFT approaches are highlighted and some of the advantages of our scheme-including the ability to correctly describe charge-transfer excitations-are critically assessed.

We have investigated the effects of O2 molecule gas adsorption on the electronic properties of semiconductor armchair hydrogenated edges graphene nanoribbons (AHEGN) via density functional theory as implemented in the code WIEN2k. The energy adsorption and electronic properties are calculated for different positions of O2. It is found that adsorption energy in the edges is lower than in the other positions. By increasing adsorption of gas concentration, the energy gap of AHEGN decreases and at a critical concentration a semiconducting-metallic phase transition takes place. This system could be used for detection of oxygen molecule gas.

The results of first principles calculations of band structure, density of states, and electron density topology of alkali metal oxalates are presented. The calculations have been carried out with WIEN2k ab initio program, using highly precise full potential linearized augmented plane wave method within density functional theory formalism. Calculated total electron density has been used in calculations of its topological properties (according to Bader’s quantum theory of atoms in molecules formalism) and Cioslowski and Mixon’s topological bond orders. The obtained results show important similarities between electronic structure and electron density topology for all analyzed structures with electronic structure close to Fermi energy typical for ionic compounds and bonding which is mainly covalent within the oxalate anion (with partly ionic character of carbon–oxygen bonds) and strongly ionic between oxalate anion and cationic sublattice. These results have been used as a basis for theoretical analysis of thermal decomposition process described in detail in part II of this paper (where also the results of additional calculations of atomic and bond valences, bond strengths and strains are presented).

First-principles band-structure augmented plane wave +local orbitals (APW+LO) calculations as incorporated in the WIEN2k code as well as X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) measurements are performed to elucidate the electronic structure of Zr4Fe2O oxide, a very prospective hydrogen-storage material. Total and partial densities of states for Zr4Fe2O are derived from the APW+LO calculations. The XPS valence-band spectrum as well as the XES Zr Lβ2,15, Fe Lα and O Kα bands are measured for Zr4Fe2O0.6 oxide. Our APW+LO calculations show that the O 2p-like states make the major contributions at the bottom of the valence band, whilst the Fe 3d- and Zr 4d-like states are the dominant contributors at the top of the valence band and at the bottom of the conduction band of Zr4Fe2O. Peculiarities of the occupation of the valence band of Zr4Fe2O predicted by the APW+LO calculations are confirmed experimentally by comparison, on the common energy scale, of the XPS valence-band spectrum and the XES bands representing the energy distributions of the Zr 4d-, Fe 3d- and O 2p-like states in the compound under consideration. In addition, the XPS Zr 3d, Fe 2p and O 1s core-level binding energies are derived for Zr4Fe2O0.6 oxide.

A new package for calculating lattice constants and equation of state for hexagonal and tetragonal structure is released. We call it as 2D-optimize. The new package is compatible with the highly accurate all-electron full-potential (linearized) augmented plane-wave plus local orbital [FP-(L)APW+lo] method implemented in WIEN2k code. This package is available with WIEN2k code. We have performed a convenient volume and c/a structure optimization by using 2D-optimize package. First, we find the best value of c/a and therefore the energy for each volume, and then for those volumes and energies the equation of state (EOS) will obtained, and after that the value of c/a calculates within optimal volume. We have done 1D and 2D search of EOS for MnAs and Mg within PBE functional and compared the results with experimental data, the results of 2D search for EOS are better than 1D search of EOS. The cell parameters and the bulk modulus of 20 hexagonal structure compounds were calculated using the new package and compared with the experimental data.

We present a module that enables computation of polarization using density functional theory based on the full potential linearized augmented plane wave package WIEN2k . The theoretical background of deriving microscopic polarization of materials using the modern theory of polarization (geometric Berry phase approach) is reviewed. The software is validated and then applied to determine spontaneous polarization and Born effective charges of several crystal structures, which are commonly studied theoretically and experimentally.

The topological band structures of LuPdBi x Sb 1− x (for x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1) alloys have been investigated using density functional theory by Wien2k package. The generalized gradient approximation (GGA) and Engel–Vosko generalized gradient approximation (GGA_EV) have been used to obtain accurate the band inversion strength and band order. The calculated results show that LuPdBi x Sb 1− x alloys for x ⩾ 0.25 in GGA and x ⩾ 0.375 in GGA_EV are candidates for three dimensional topological insulator or topological metal. Furthermore the effect of hydrostatic pressure on band inversion strength and band order of these alloys has been investigated.

Very recently (2012, Phys. Rev Lett., 109, 035502) a new hexagonal (s.g. P63/mmc, ♯194) ternary phase Nb2GeC, which belongs to so-called 211-like MAX phases, was discovered. In order to get a systematic insight into the structural, elastic, and electronic properties of Nb2GeC, we used two complementary DFT-based first-principles approaches (as implemented in the VASP and Wien2k packages) to calculate the optimized structural parameters, band structure, densities of state, Fermi surface, and a set of elastic parameters: elastic constants (Cij), bulk modulus (B), compressibility (β), shear modulus (G), Young’s modulus (Y), and elastic anisotropy indexes, which were discussed in comparison with available data. Besides, the inter-atomic bonding picture for Nb2GeC was discussed using electron density maps and Bader’s charge analysis.

The G W method has become the state-of-the-art approach for the first-principles description of the electronic quasi-particle band structure in crystalline solids. Most of the existing codes rely on pseudopotentials in which only valence electrons are treated explicitly. The pseudopotential method can be problematic for systems with localized d - or f -electrons, even for ground-state density-functional theory (DFT) calculations. The situation can become more severe in G W calculations, because pseudo-wavefunctions are used in the computation of the self-energy and the core–valence interaction is approximated at the DFT level. In this work, we present the package FHI-gap , an all-electron G W implementation based on the full-potential linearized augmented planewave plus local orbital (LAPW) method. The FHI-gap code can handle core, semicore, and valence states on the same footing, which allows for a correct treatment of core–valence interaction. Moreover, it does not rely on any pseudopotential or frozen-core approximation. It is, therefore, able to handle a wide range of materials, irrespective of their composition. Test calculations demonstrate the convergence behavior of the results with respect to various cut-off parameters. These include the size of the basis set that is used to expand the products of Kohn–Sham wavefunctions, the number of k points for the Brillouin zone integration, the number of frequency points for the integration over the imaginary axis, and the number of unoccupied states. At present, FHI-gap is linked to the WIEN2k code, and an implementation into the exciting code is in progress.

The low-loss region of the electron energy-loss spectrum, the valence EELS, provides information about the electronic structure and optical properties of materials. For bulk materials the spectral intensity can be directly connected to the complex dielectric function. Ab initio quantum mechanical calculations have an important role to play in the interpretation of the fine spectral detail and how this can be connected to the material properties. This paper provides an overview of theoretical background to the calculation of valence EELS in bulk solids and gives specific details on how to run such calculations using the WIEN2k code. The comparison of Au and AuAl(2) illustrates how in metals such calculations are successful in reproducing the main spectral details and can be used to understand the origin of the different colours of these two metals.

Nowadays, it had been discovered that spontaneous spin polarization that increases the magnetization interest, particularly in the perovskites oxides. The First-principle calculation has played an important role in most of the modeling and simulation studies investigated. The DFT-GGA and DFT + U–GGA + U (Density Functional Theory-Generalized Gradient Approximation and the Density Functional Theory with the corrected U-Hubbard Hamiltonian–Generalized Gradient Approximation + U-Hubbard term) are introduced here to compute the YMnO3 perovskite oxide using the Wien2K code. New theoretical model on the electronic structure and the spin effect is given for the considerable oxide by investing the cubic phase. Different magnetic configurations (ferromagnetic and anti-ferromagnetic) are given for this type of structure. The implementation of the U-Hubbard term in our calculation allows more comprehension on the YMnO3 behavior and has ameliorated the obtained results. The lattice parameter of the hexagonal 4H-four layered structure is also given. We aim to compare between the two approaches employed in the present paper GGA and GGA + U, whereas we show that the (U-J) term has played the important role in the current study. The magnetic moment is also calculated using both approaches and discussed. Our results agree very well with the theoretical and experimental data. The considerable perovskite oxide exhibits the A-type anti-ferromagnetic (A-AFM) character.