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The work is devoted to the issue of the rational use of the solar energy in the technological process of fruit drying based on the use of solar drying devices, which are applied in various sections of the agro-industrial centers of Ukraine. The aim of this research was intensification of the fruits drying process using the solar energy by combining an air collector and drying chamber into a single power unit. To achieve the aim the heat exchange diagnostic techniques with alternative potentials of diffusion and moisture transfer was developed. This technique differs from those existing for the heat exchange research in that it allows the intensity of the moisture evaporation from a unit of the material surface to be calculated, based on the synthesis of the moisture content and the irreversible major laws of processes of the heat exchange characteristics of the fruits drying using the solar dryer. The above model makes it possible to diagnose the heat exchange processes and analyze the mathematical model of the heat exchange processes. It also allows modeling the changeable diffusion and moisture transfer potentials based on the dependences obtained and for the purpose of a further application in the methods and devices development to control the strain-deformed state of the fruits during the drying process. The method is offered for the calculation of diffusion and moisture transfer during drying fruits in the solar dryer.

The focus of this study is the structural, electronic, and magnetic characteristics of the ZnSeTe solid solution with chromium impurity. The structure of this solid solution was determined in two steps. At the first stage the internal coordinates of atoms are optimized, and at the second one the lattice parameter relaxation, including re-optimization of internal coordinates, were done. Further, after the introduction of Cr substitution impurity, electronic energy spectra and densities of electronic states were calculated. Significant changes in parameters of the electronic structure and magnetic properties caused by cationic vacancy were revealed. It was found that the doped solid solution of Cr:ZnSeTe is a semiconductor for both electron spin polarizations. The study of the supercell with a cationic vacancy revealed significant differences in the parameters of electronic energy bands as well as magnetic properties, compared with those in crystal with no defects. [ABSTRACT FROM AUTHOR]

First, this work examines the structural characteristics of the formation of a ZnSeTe solid solution. Further, after the introduction of Fe substitution impurity, electronic energy spectra and densities of electronic states were calculated. Significant changes in parameters of the electronic structure and magnetic properties caused by external hydrostatic pressure were revealed. It was found that the doped solid solution of ZnFeSeTe under normal conditions is a semiconductor for both spin orientations. However, under the action of hydrostatic pressure, this material turns into a metallic state, since the 3d states of iron are now at the Fermi level. Under the influence of pressure, the magnetic moment of the supercell decreases by more than six times, that is, from 4.0 to 0.67 Bohr magnetons. [ABSTRACT FROM AUTHOR]

The influence of hydrostatic pressure and cationic vacancies on the electronic and magnetic properties of the ZnTe:Mn crystal is investigated. First-principles calculations have been carried out for the supercell 2 × 2 × 2, containing 64 atoms, using the ABINIT code. The hybrid exchange–correlation functional PBE0 was used to correctly describe the strongly correlated 3d-electron subsystem. The Hamiltonian matrix was calculated on the one-electron basis of the projector augmented waves. At the first stage, the calculations were performed in the ambient and compressed states of the material. In the second stage, we have evaluated the electronic properties in the ZnTe:Mn material taking into account the simultaneous effect of the cationic vacancies and the hydrostatic pressure. It was found that for both uncompressed and compressed states of the material, the introduction of the cationic vacancies leads to its transition to the metallic state. A significant influence of the cationic vacancies on the value and nature of the resulting magnetic moment of the supercell was also revealed. Based on the results obtained in this paper, an assumption is made about a non-collinear model of magnetism in the material caused by cationic vacancies. [ABSTRACT FROM AUTHOR]

In the present paper, the way to describe the energy spectrum, wave function, and self-consistent potential in a semiconductor with a sphalerite structure at a predetermined temperature is proposed. Using this approach, within the framework of the supercell method, the temperature dependences of the ionization energy of intrinsic acceptor defects in cadmium telluride are calculated. In addition, on the basis of this method, the temperature dependences of the heavy hole effective mass, optical and acoustic deformation potentials, as well as the heavy hole scattering parameters on ionized impurities, polar optical, piezooptic and piezoacoustic phonons are established. Within the framework of short-range scattering models, the temperature dependences of the heavy hole mobility and the Hall factor in CdTe crystals with defect concentrations of 1 x 1020 1022 cm – 3 are considered. [ABSTRACT FROM AUTHOR]

The electronic and magnetic properties of ZnS crystal with impurities of transition 3d elements Cr and Fe, which replace Zn atoms, are calculated. The calculations are performed in 2×2×2 sphalerite supercells containing 64 atoms. The same supercells, which contain both Cr and Fe impurities, are also considered. It is established that energies of 3d electrons of the Cr atom with spin up in the Zn31Cr1S32 supercell are localized in narrow energy intervals around the Fermi level and at the top of the valence band. For spindown states, this material exhibits the properties of a semiconductor with a direct band gap of 2.11 eV. The magnetic moment of the supercell equals to 4 μB. The results of the calculation for the Zn31Fe1S32 supercell show that this material is a direct-band semiconductor with the width of the band gap at the Γ point of about 1.96 eV. 3d electrons with spin down are localized in narrow energy bands near the Fermi level and at the bottom of the conduction band. The pseudogap value for electrons with spin down is 0.53 eV. The magnetic moment of the supercell is also equal to 4 μB. It is found from the results of the calculation for the Zn30Cr1Fe1S32 supercell that 3d electrons of the Cr atom with spin up are localized in the vicinity of the top of the valence band and the Fermi level, which is inside the valence band. The optical gap at the Γ point is equal to 0.60 eV and the indirect fundamental gap (Γ – R) is 0.59 eV. The pseudogap value for electrons with spin down is 0.60 eV. The magnetic moment of the supercell equals 8.04 μB. The calculations are performed using the ABINIT program. The hybrid exchange-correlation functional PBE0 is used to eliminate the self-interaction error of Cr and Fe 3d electrons. [ABSTRACT FROM AUTHOR]

The electronic energy band spectra of CdX crystals (X = O, S, Se, Te) in the wurtzite phase have been calculated. We have revealed that Cd 4d electrons are localized in the narrow energy intervals of the valence band. The results obtained here show that the exchange-correlation functionals developed within the LDA and GGA approaches are not applicable to the strongly correlated 4d electron subsystem. Indeed, the band gap found for the CdO crystal in these approaches is Eg = 0, and its values for CdS, CdSe, and CdTe materials are 1.48, 0.67, and 0.84 eV, respectively. They all are much smaller than the measured Eg for CdX materials, which are 0.91, 2.5, 1.8 and 1.8 eV, respectively. We found that “GGA – Green’s function” calculation scheme, which is very effective for s-p electron systems, did not produce successful results for CdX crystals. That is why we have chosen a combination of “hybrid functional – Green’s function” approach. The Eg values found in CdX crystals without spin-orbit interaction are 0.90, 2.49, 1.92 and 2.10 eV, respectively. The spin-orbit interaction causes a negligible narrowing dESO of the Eg parameter in CdO and CdS crystals. However, in CdSe and CdTe materials, the narrowing parameter dESO values are 0.12 and 0.27 eV, respectively. Corrected by dESO band gaps of CdSe and CdTe crystals have the values of 1.80 and 1.83 eV, respectively. The Eg values found here are well compared with the experiment. It is found that the energy bands of the semicore Cd 4d electrons obtained without spin-orbit interaction overlap in CdX crystals. Spin-orbit interaction leads to a widening of Cd 4d energy bands. Moreover, in CdSe and CdTe crystals, the spin-orbit interaction leads to a clear separation of 4d electron energy bands into two parts, the lower of which contains 8 and the upper 12 branches of the spectrum. [ABSTRACT FROM AUTHOR]

In this work the electronic properties of the MnCoSi half-Heusler alloy are evaluated within the formalism of the electron density functional. The calculations are made using ABINIT code in two approaches. They are based on the projector augmented waves (PAW) and on the norm-conserving pseudopotentials (NCPP). The hybrid exchange-correlation functional PBE0, which allows to remove partly the self-interaction of strongly correlated 3d electrons of Co and Mn atoms, is implemented on the PAW basis. The electronic energy spectra of the MnCoSi crystal in the magnetic and nonmagnetic phases have been evaluated in the PAW basis states. In the process of optimizing the crystal structure, the interpolants of total energy E(V) and pressure P(V) as the functions of volume, and V(P) as a function of pressure are found. Based on these dependencies, the bulk modulus B0 = 196.1 GPa is found. As established, in the magnetic state the MnCoSi material is a metal for spin up and a semiconductor for spin down. In the non-magnetic state, the material is a metal. Electronic properties are obtained for the uncompressed and compressed states of the crystal. The pressure dependencies of the magnetic moment of atoms are also found. Within the second approach (NCPP), the elastic constants c11, c12, and c44 are calculated, from which the moduli of elasticity, a sound waves velocities, and Debye temperature are derived. The bulk modulus B0 = 197.1 GPa found in this approach is well compared with one obtained on the PAW basis. [ABSTRACT FROM AUTHOR]

The papers presents the results of the theoretical calculations of the partial and total density of states of LaF3:Sm and LaF3:Pm crystals. We analyze the positions of 4f and 5d energy states of activator ions in the energy structure of the host material. We calculated and described electronic energy band structures of the above mentioned crystals. We made a quantitative and qualitative comparison between the energy structure of LaF3:Sm and LaF3:Pm crystals. [ABSTRACT FROM AUTHOR]

The three-stage calculation of the electronic and optical properties of T-phthalocyanine, where T {Mn, Fe, Co, Ni, Cu, Zn}, has been performed. On the first stage, the hybrid functional PBE0 of the exchange-correlation energy was employed. The use of the hybrid functional has enabled us to obtain better energy levels of the semi-core 3d electrons of the T-elements. The crystal wave functions, electron densities, potentials and the electronic energy band spectrum formed the basis for the second stage of the calculations. The second stage was made on the basis of Green’s function (GF) approach, namely, on the first order of perturbation theory, called the GW approximation. This approximation clearly takes into account the electron and hole, but only in the static version of their interaction. In the formalism of the GF, we obtained a quasi-particle spectrum of electrons and holes, which agrees very well with the experiment. Therefore, having completed the second stage of the calculations, we have obtained a good basis for performing the third stage, namely for calculating the optical properties of the materials under consideration. The third stage has been done within the Bethe-Salpeter equation (BSE). Within this approach, the electron and hole move, in contrast with PBE0 and GW methods. Optical absorption obtained from the BSE approach illustrates better agreement with measured data for all the materials considered here. [ABSTRACT FROM AUTHOR]

Ab initio investigation of the two porous coordination polymers Cu[Cu(pdt)2] and Cu[Ni(pdt)2] has been performed. The dispersion laws and partial density of states was obtained with the PBE0 hybrid functional. The results found here show that the materials under consideration are degenerate p-type semiconductors. Here, the effect of partial self-interaction removing of the strongly correlated 3d electrons of Cu and Ni was examined. In case of Cu-containing materials, the obtained results con1rm that the 3d electrons of Cu reveal strong correlations, and, therefore, their electronic properties could be evaluated by means of a hybrid functional of the exchange-correlation energy. We also obtained quasiparticle properties within the Green's function (G0W0) and Bethe-Salpeter approaches. The last one was used in order to examine excitonic properties in the degenerate semiconductors. The imaginary part of the dielectric function was obtained within random-phase approximation as well as the Bethe-Salpeter approach. [ABSTRACT FROM AUTHOR]

We have found that the energies of the Zn semicore 3d electrons in crystals ZnX (X = O, S, Se, Te), in the wurtzite phase, are localized in narrow intervals within the valence band. It was found that the widths of these intervals at Γ point of the first Brillouin zone are equal to 1.24, 0.68, 0.50 and 0.40 eV for ZnO, ZnS, ZnSe and ZnTe crystals, respectively. It was found that the wave functions of the Zn 3d electrons strongly overlap with the states of the valence and the conduction bands. Consequently, the widely used exchange-correlation energy functionals, constructed in the LDA and GGA-PBE approaches, are inappropriate for systems with narrow band of highly correlated 3d electrons. That is why we performed calculations based on the hybrid exchange-correlation energy functional, HSE06, and the obtained eigenenergies and eigefunctions were used in the construction of the Green's function. Consequently, the basis of this study is based on the two modern concepts of electronic theory of crystals, namely the hybrid exchangecorrelation functional and quasiparticle approach. The values of the bandgap, Eg, obtained here in the GGA-PBE approximation, are well-matched to the results found by other authors. The values of Eg, calculated using the combination of Green's function methods and the hybrid functional for the exchangecorrelation energy, HSE06, are equal to 2.34, 3.28, 2.35 and 2.13 eV for ZnO, ZnS, ZnSe and ZnTe crystals, respectively, if the mixing factor in the functional is 0.25, that it is the standard. We calculated the electron energy spectra for ZnO, ZnS, ZnSe and ZnTe crystals, with mixing factors, different from the standard ones, namely of 0.40, 0.375, 0.35 and 0.325. The corresponding band gaps have been acquired the values of 3.29, 3.83, 2.81 and 3.43 eV, which are very well matched with the experiment. [ABSTRACT FROM AUTHOR]

The influence of strong d-electron correlations on the values of the parameters of the electron energy bands in the solid solution Cd1-xMnxTe (x = 0.25) was studied. At the first stage, the spin-resolved electronic energy bands were obtained in the GGA approach. At the second stage, strong correlations were taken into account for the Mn d-electrons by means of the hybrid exchange-correlation function PBE0, and at the third stage, correlations of the Mn and Cd d-electrons were included simultaneously. It was revealed that the material is a semiconductor for both spin channels. Found that for spin-up electrons, after taking into account the strong correlations of the Mn 3d-electrons, the top of the valence band was shifted by - 0.10 eV, and the bottom of the conduction band has increased by 0.02 eV, which resulted in an increase in the band gap, Eg, by 0.12 eV. Strong correlations of the Cd 4d-electrons add to an increase in Eg a value of 0.03 eV. The total increase in Eg for spin-up electrons is equal to 0.15 eV. For the spin-down electrons, the inclusion of strong 3d-electron correlations of Mn led to an increase in the top of the valence band by 0.12 eV, and the bottom of the conduction band has increased by 0.54 eV, resulting in an increase in the band gap by 0.42 eV. Strong correlations of the Cd 4d-electrons add to an increase in Eg a value of 0.02 eV. The total increase in Eg for spin-down states equals 0.44 eV. It was found that for spin-up electrons, the value of Eg of solid solution, without taking into account strong correlations of d-electrons, is 1.32 eV, and the inclusion of 3d-electron correlations of Mn leads to the Eg value of 1.44 eV. And the additional inclusion of 4d-electron correlations of Cd gives the Eg value of 1.47 eV. It was found that for spin-down electrons, the value of Eg of a solid solution, without taking into account the strong correlations of d-electrons, is 1.69 eV, and the inclusion of 3d-electron correlations of Mn leads to the Eg value of 2.11 eV. And the accounting of 4d-electron correlations of Cd has caused only a slight increase in the Eg to 2.13 eV. [ABSTRACT FROM AUTHOR]

The Green’s function method, implemented in the first order of the perturbation theory (GW), was applied for an accurate description of the electronic structure of cubic BaSnO3 and SrSnO3 perovskites. First, the band structure of these materials was calculated within the generalized gradient approximation (GGA). Then, in order to obtain the accurate band gaps, the quasiparticle corrections to the eigenenergies were evaluated. The calculated electronic structure by means of the GW approximation was compared to the structure obtained within the GGA. The application of quasiparticle corrections to the eigenenergies led to a significant widening of the band gaps and provided a much better agreement with the experimental data. The GW corrections to the band energies, found for both crystals at the points of the first Brillouin zone, are quite different. Consequently, the use of a scissor operator can lead to errors in a calculation of the optical constants. [ABSTRACT FROM AUTHOR]