Ab initio study of the electronic and magnetic properties of vanadium-doped and vacancy-defected chalcopyrite semiconductor ZnSnAs 2 was carried out using density functional theory within the spin generalized gradient approximation with Hubbard-like correction (SGGA + U ). Investigation of magnetic properties shows that adding a transition element contributes to the magnetization of ZnSnAs 2 . The total energy calculations for a number of supercells show that a ferromagnetic spin ordering is favorable when V replaces Zn . The ferromagnetic alignment in V -doped ZnSnAs 2 systems behaves half-metallic state. The presence of a single Zn - or Sn - or As -vacancy affects the ferromagnetism and may even strengthen the magnetization of V -doped ZnSnAs 2 .

In this article, the structural and electronic properties of bulk ZnO have been studied using the plane-wave-based pseudopotential density functional theory (DFT). The structural parameters, band structure (BS), and density of states (DOS) of ZnO wurtzite structure have been investigated by Quantum Wise within LDA (GGA) and LDA (GGA)+U methods by Fritz-Haber-Institute (FHI) pseudopotentials. The calculated band gaps using Hubbard U semiempirical corrections are in agreement with previous experimental works and shows both the valence band maximum and conduction band minimum located at the Γ point of the Brillouin zone (BZ).

This paper presents the results of first-principle calculations of the magnetic properties of vanadium-doped and a vacancy-defected chalcopyrite semiconductor ZnSnAs 2 . It was shown that adding a transition element contributes to the magnetization of ZnSnAs 2 . The calculations for a number of supercells showed that a ferromagnetic spin ordering is favorable when V substitutes Sn. Besides, the Zn, Sn and As vacancies affect the magnetization. While V(Sn) substitution of the vacancies strengthens magnetization, a slight weakening of the magnetization occurs due to the arsenic atoms. Four As atoms chemically bonded to V dopant were found to be most contributive.

In this work, we report the effect of the spin–orbit (SO) interaction on the band structure of TlInSe2. Calculation was performed by implementing density functional theory (DFT) method. Our results show that SO interaction is significant for two high symmetrical point ([Formula: see text], [Formula: see text]) and line ([Formula: see text], [Formula: see text]) of Brillouin zone in the band structure and negligible changes was observed in the bands near the Fermi level. The maximum SO splitting is [Formula: see text]0.9 eV.

The electronic and magnetic properties of ZnO containing Cr doped atoms and Zn and O vacancies in its crystal structure are theoretically investigated. Calculations are performed using Atomistix Tool Kit and Vienna Ab-initio Simulation Package software implementing the electron density functional theory method with the Hubbard correction. It is shown that the magnetic moment of a defect supercell strongly depends on the impurity concentration and presence of vacancies. The doping of an oxygen atom increases the probability of zinc-vacancy formation.

AbstractThe electronic and magnetic properties of ZnO containing Cr doped atoms and Zn and O vacancies in its crystal structure are theoretically investigated. Calculations are performed using Atomistix Tool Kit and Vienna Ab-initio Simulation Package software implementing the electron density functional theory method with the Hubbard correction. It is shown that the magnetic moment of a defect supercell strongly depends on the impurity concentration and presence of vacancies. The doping of an oxygen atom increases the probability of zinc-vacancy formation.

We have studied the band structure and the band gap closure of TlInSe2 under pressure in the range of 0 GPa to 21 GPa, by employing the first-principles method based on the density functional theory. We discuss the possible metallic transition in the tetragonal phase of TlInSe2 crystal. Our calculation results show that the value of the pressure at the crossover from the direct to the indirect gap is found to be 8 GPa. The "semiconductor-metal" transition is determined to occur at 14 GPa. The study of the pressure effect on the effective masses for semiconductor state shows that with increasing pressure, the effective masses of holes and electrons decrease and the anisotropy of effective masses of holes is weakening.

Electronic band structure and defect formation energy of TlGaSe 2 are studied using density functional method within the Local Density Approximation.Calculated band structure shows that the top of valence band and the bottom of conduction band locate at the symmetry point  and along the symmetry line -Y, respectively.The defect formation energy is calculated as the difference between the total energy of a stable structure and the relaxed defect structure at constant volume.Calculation is done for the five charge states: 2, 1, 0, 1, 2.Energies of vacancies' (V Tl , V Ga , V Se ) formation are determined for the TlGaSe 2 crystal consisting of 63 atoms for the various charge states as a function of Fermi energy.The calculated optical properties indicate that the optical energy gap is increased due to the Se and Tl vacancies.

The electronic structure, density of states (DOS), effective mass are calculated for tetragonal TlInSe 2 from first principle in the framework of density functional theory (DFT). The electronic structure of TlInSe 2 has been investigated by Quantum Wise within GGA. The calculated band structure by Hartwigsen–Goedecker–Hutter (HGH) pseudopotentials (psp) shows both the valence band maximum and conduction band minimum located at the T point of the Brillouin zone. Valence band maximum at the T point and the surrounding parts originate mainly from 6s states of univalent Tl ions. Bottom of the conduction band is due to the contribution of 6p-states of Tl and 5s-states of In atoms. Calculated DOS effective mass for holes and electrons are [Formula: see text], [Formula: see text], respectively. Electron effective masses are fairly isotropic, while the hole effective masses show strong anisotropy. The calculated electronic structure, density of states and DOS effective masses of TlInSe 2 are in good agreement with existing theoretical and experimental results.

Представлены результаты расчетов из первых принципов в рамках теории функционала плотности электронного спектра кристаллов TlFeS2 и TlFeSe2 в антиферромагнитной фазе. Исследованы происхождения зон из s-, p-, d-электронных состояний атомов Tl, Fe, S, Se. Установлено, что в этой фазе кристаллы обладают полупроводниковыми свойствами. Величины запрещенной зоны 0.05 эВ (TlFeS2) и 0.34 эВ (TlFeSe2) соответственно. DOI: 10.21883/FTP.2017.04.44341.8290

From first principles, in the pressure range of 0–20 GPa, taking into account the structural phase transition at 3 GPa, all independent elastic constants of GaS compound have been calculated. From obtained data, the pressure dependences of the velocities of propagation of elastic waves in different symmetry directions have been determined. The values of averaged elastic moduli, Young’s modulus and Poisson’s ratio and their pressure dependence have also been calculated..

The pressure dependences of the phonon frequencies of the Brillouin zone center and also the elastic constants of the GeSe compound have been calculated by the density functional theory method using the ABINIT program package. The results have been compared with the available data of theoretical calculations and measurements of the pressure dependences of the Raman frequency. The calculations have demonstrated that the compound undergoes a continuous phase transition from the simple orthorhombic to body-centered orthorhombic lattice at a pressure about 29 GPa.

The IR- and Raman-active phonon frequencies, as well as the elastic constants of orthorhombic GeSe, were calculatedas a function of hydrostatic pressure using the method of density functional in the ABINIT software package. Comparison with the published results of theoretical calculations and experimental data of the pressure dependence of Raman-active phonons has been carried out. Our calculations show that at a pressure of about 29 GPa the crystal structure of GeSe undergoes a continuous transition from simple orthorhombic to base-centered orthorhombic lattice.

In this paper we present the results of ab initio first-principle calculations of the lattice dynamics of ternary TlInS2 semiconductor with highly anisotropic crystal structure. Calculations have been performed using the open-source code ABINIT on the basis of density functional theory within the plane-wave pseudopotential approach. The basis of plane waves was truncated at electron kinetic energy of 40 Ha. Integration over the Brillouin zone was carried out using a 2 × 2 × 2 grid. The equilibrium structure was determined by minimizing the total energy with respect to the lattice constants and the internal structural parameters. The results are discussed in terms of previously existing experimental data. It is shown that along the layer, the low-frequency acoustic branch displays the bending wave behavior that is typical for crystals having a layered structure.

The first-principles calculations of the lattice dynamics of the TlGaSe2 ternary semiconductor compound are presented in this paper. Calculations were performed using open-source code ABINIT on the basis of the density functional perturbation theory within the plane-wave pseudopotential approach. Results on the frequencies of phonon modes in the centre of Brillouin zone and the dispersion of transverse shear acoustic branch of the phonon spectra agree well with experimental data on Raman scattering, infrared reflectivity and ultrasound wave propagation in TlGaSe2. The calculated and experimental temperature dependencies of heat capacity are in a good agreement up to the room temperature. Along the layer, the low-frequency acoustic branch displays the bending wave behavior which is characteristic of the layer crystal structures. We have calculated also the elastic compliances tensor, the directional Grüneisen functions and the coefficients of the linear thermal expansion for TlGaSe2. We obtained that both principal components of the coefficients of linear expansion are positive in the range of temperature above 5 K.

In this paper we present the results of ab initio calculations of the lattice dynamics of ternary TlGaS2 semiconductor with highly anisotropic crystal structure. Calculations have been performed using the open-source code ABINIT on the basis of density functional theory within the plane-wave pseudopotential approach. The results are discussed in terms of previously existing experimental data. Calculated frequencies of the phonon modes at the center of the Brillouin zone, as well as calculated IR reflection spectra in the range of 15-500 cm(-1) are in reasonable agreement with existing experimental data. The theoretical temperature dependence (up to room temperature) of the heat capacity is in good agreement with experimental data. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We present the first-principles calculation of the lattice dynamics of the TlGaSe2 ternary semiconductor having highly anisotropic crystal structure. Calculations have been performed using open-source code ABINIT on the basis of the density functional perturbation theory within the plane-wave pseudopotential approach. Results on the frequencies of phonon modes in the centre of Brilloin zone and the dispersion of transverse shear acoustic branch of the phonon spectra agree well with the experimental data on Raman scattering, infrared reflectivity and ultrasound wave propagation in TlGaSe2. The calculated and experimental temperature dependencies of heat capacity are in a good agreement up to the room temperature. Along the layer, the low-frequency acoustic branch displays the bending wave behavior which is characteristic of the layer crystal structures.