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1
MUN, B. S., M. WATANABE, M. ROSSI, V. STAMENKOVIC, N. M. MARKOVIC, and P. N. ROSS. "THE STUDY OF SURFACE SEGREGATION, STRUCTURE, AND VALENCE BAND DENSITY OF STATES OF Pt3Ni(100), (110), AND (111) CRYSTALS." Surface Review and Letters 13, no. 05 (October 2006): 697–702. http://dx.doi.org/10.1142/s0218625x06008682.
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The surface segregation, structure, and valence band density of states of Pt 3 Ni (100), (110), and (111) single crystals are characterized with low energy ion scattering (LEIS), low energy electron diffraction (LEED), and ultraviolet photoemission spectroscopy (UPS). The results of LEIS clearly reveal the complete surface segregation of Pt to the top layer on all crystal alloys. LEED indicates the (5 × 1) surface reconstruction on the Pt 3 Ni (100), while (110) and (111) surfaces show (2 × 1) and (1 × 1) patterns, respectively, identical to Pt single crystals. The valence bands density of states on Pt 3 Ni alloys are compared to those of Pt single crystals via UPS measurements.
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PENG, J. L., SHAUN BULCOCK, PETER I. BELOBROV, and L. A. BURSILL. "SURFACE BONDING STATES OF NANO-CRYSTALLINE DIAMOND BALLS." International Journal of Modern Physics B 15, no. 31 (December 20, 2001): 4071–85. http://dx.doi.org/10.1142/s0217979201007865.
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The rough surface of nano-crystalline diamond spheres induces surface electronic states which appear as a broadened pre-peak over approx. 15 eV at the C K-edge energy threshold for carbon in the parallel electron energy loss spectrum (PEELS). This appears to be at least partially due to 1s-π* transitions, although typically the latter occupy a range of only 4 eV for the sp2 edge of highly-oriented pyrollytic graphite (HOPG). No π* electrons appear in the conduction band inside the diamond particles, where all electrons are sp3 hybridized. PEELS data were also obtained from a chemical vapour deposited diamond film (CVDF) and gem-quality diamond for comparison with the spectra of nano-diamonds. The density of sp2 and sp3 states on the surface of diamond nano-crystals is calculated for simple structural models of the diamond balls, including some conjecture about surface structures. The results are used to interpret the sp2/sp3 ratios measured from the PEELS spectra recorded as scans across the particles. Surface roughness at the atomic scale was also examined using high-resolution transmission electron microscopy (HRTEM) and electron nano-diffraction patterns were used to confirm the crystal structures.
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Liu, Xiao Qing, Rui Fang Zhang, Yi Guo Su, and Xiao Jing Wang. "Study on the Energy Band Structure of La Doped ZnO." Advanced Materials Research 233-235 (May 2011): 2119–24. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.2119.
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The energy bands of La -doped ZnO were studied systematically by the density functional theory (DFT). Based on the data of the band structure, DOS (Density of State) and PDOS( Partial Density of States), atomic populations and net charge, the influence on the energy band structure of the macrostructure of ZnO and La-doped ZnO was investigated. The results showed that the free electrons were produced by the doping of La on (or in) ZnO crystal. The Fermi energy was shifted up to the conduction band, making the ZnO particles having the characters of degenerated semiconductor. The excitation from impurity states to the conduction band may account for the blue shift of the absorption edge in the model of La-doped ZnO. Comparison with the different models of the La doped/loaded on the ZnO surface, La atoms loaded on the surface of ZnO and La atoms replaced of Zn atoms on the ZnO surface, the shift to the lower energy location were found after La doping/loading. The more shift and the large band gap was found for the model of La doped on the Zn position in the ZnO crystal.
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Donath, Markus. "Spin-polarised Electron Studies of Low-dimensional Magnetic Systems." Australian Journal of Physics 52, no. 3 (1999): 579. http://dx.doi.org/10.1071/ph99006.
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Spin-polarised electrons provide unique experimental access to magnetic properties of surfaces and layered structures. The combined use of different techniques allows us to develop a microscopic picture of the physics underlying the macroscopic magnetic properties, e.g. magnetic phase transitions, magnetic coupling phenomena, exceptional surface magnetic properties. In this paper, two techniques are described together with the kind of questions addressed by them. Spin-resolved appearance potential spectroscopy gives local magnetic information about multi-component systems by probing the spin-dependent local density of unoccupied states. Spin-resolved inverse photo-emission measures specific electron states above the Fermi level. In particular, two-dimensional states serve as magnetic sensors at surfaces. Examples from surfaces as well as thin-film structures of band and local-moment ferromagnets are presented.
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Ahuja, Babu Lal, Ashish Rathor, Vinit Sharma, Yamini Sharma, Ashvin Ramniklal Jani, and Balkrishna Sharma. "Electronic Structure and Compton Profiles of Tungsten." Zeitschrift für Naturforschung A 63, no. 10-11 (November 1, 2008): 703–11. http://dx.doi.org/10.1515/zna-2008-10-1114.
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The energy bands, density of states and Compton profiles of tungsten have been computed using band structure methods, namely the spin-polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) approach as well as the linear combination of atomic orbitals with Hartree-Fock scheme and density functional theory. The full potential linearized augmented plane wave scheme to calculate these properties and the Fermi surface topology (except the momentum densities) have also been used to analyze the theoretical data on the electron momentum densities. The directional Compton profiles have been measured using a 100 mCi 241Am Compton spectrometer. From the comparison, the measured anisotropies are found to be in good agreement with the SPR-KKR calculations. The band structure calculations are also compared with the available data.
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HONG, SOON C., and JAE IL LEE. "ELECTRONIC STRUCTURE OF THE Mo(001) SURFACE: LOCAL DENSITY STUDY." International Journal of Modern Physics B 07, no. 01n03 (January 1993): 524–27. http://dx.doi.org/10.1142/s0217979293001104.
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LEED observed an incommensurate surface reconstruction for the Mo(001) surface and a recent photoemission experiment measured electronic structure of the Mo(001) surface at room and low temperature (52 K). Employing the all-electron local density full potential linearized augmented plane wave (FLAPW) method, we calculated the electronic structure of the Mo(001) surface. Two prominent LDOS peaks at the surface are found just below Fermi level and E b = 0.50 eV and they are confirmed to come from surface states along [Formula: see text] symmetry line. The surface states (just below Fermi level) with even symmetry show no energy dispersion while the surface states ( E b = 0.50 eV ) with odd symmetry have upward energy dispersion from [Formula: see text] to [Formula: see text]. The two bands of surface states fade off at [Formula: see text], which is very consistent with experiments. The work function is calculated to be 4.20 eV. We will present the character of charge densities of the surface states and compare to experiments.
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REFOLIO, M. C., J. M. LÓPEZ SANCHO, M. P. LÓPEZ SANCHO, and J. RUBIO. "CORRELATION EFFECTS IN PHOTOEMISSION SPECTROSCOPY: Cl/Si(100)-(2 × 1)." Surface Review and Letters 04, no. 05 (October 1997): 923–27. http://dx.doi.org/10.1142/s0218625x9700105x.
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Different calculations of the electronic structure of this system have been unable to explain satisfactorily some puzzling features of the experimental surface band structure measured by angle-resolved photoemission (namely, the absence of any adsorbate structure near the Fermi level and the extremely small dispersion of all the adsorbate bands). Here we present a new calculation based on the lattice Anderson model in the (adsorbate) low-density regime. The one-electron Green function is computed directly from its Lehmann representation in terms of N-1 and N+1 electron states. These are obtained approximately with a new configuration interaction approach supplemented by renormalization group techniques in order to include iteratively states with an increasing number of electron–hole pairs. The resulting spectral function is in quantitative agreement with the photoemission spectrum: (1) all the adsorbate features lie between 5 and 10 eV below the Fermi level and (2) the adsorbate band dispersion is small (less than 0.5 eV). We also compare with the random phase approximation.
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Ushio, Hideki, and Hiroshi Kamimura. "III. Energy Bands, Fermi Surfaces and Density of States of the Hole Carriers in the Presence of the Local Antiferromagnetic Ordering." International Journal of Modern Physics B 11, no. 32 (December 30, 1997): 3759–96. http://dx.doi.org/10.1142/s0217979297001933.
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We have separated a hole carrier and a localized spin, by treating the exchange interaction between the spins of a carrier hole and a localized spin in a mean field sense. Then we have constructed the effective one-electron-type band structure for the hole carriers in the presence of the antiferromagnetic (AF) ordering of the localized spins. In the case of the undoped La2CuO4 all the energy bands are fully occupied by electrons so that La2CuO4 is an insulator. In this sense the present energy bands which include the many body effect fully is completely different from the ordinary energy band in the local density functional method. The top of the highest valence band is at (π/a, π/a, 0)-point, and the calculated Fermi surface is small as far as the spin correlation length of the AF order is larger than the mean free path. Based on this energy band and Fermi surfaces we have calculated various normal state properties and explained their anomalous features, such as the x-dependence of the electronic specific heat, the linear temperature dependence of the resistivity down to T c , the x-dependence of the Hall coefficient with the sign change, the large T dependence of R H , the incommensurate peak of the neutron scattering and the instability at x=0.125.
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Su, Hong Bin, Ping Yang, Jin Biao Wang, and Nan Huang. "First-Principles Calculations on the Geometry and Electronic Structure of Rutile TiO2 (110) Surface." Advanced Materials Research 79-82 (August 2009): 1201–4. http://dx.doi.org/10.4028/www.scientific.net/amr.79-82.1201.
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In this paper, both geometrical and electronic properties of rutile TiO2 (110) surfaces have been investigated using First-Principles Density-Functional calculations with CASTEP code, the model of stoichiometric surface is a (2x1) super-cell which has 12 atomic-layer slabs with the bottom 6 held fixed, the bridging-oxygen vacancy surface has been constructed by removing a neutral bridging oxygen atom from this surface. For the stoichiometric surface, the atom relaxations are: Ti6f (+0.2865Å), Ti5f (-0.1039Å), O3f (+0.2433Å) and Ob (+0.0075Å), we find no reconstruction and no surface states in the band gap, the density of states (DOS) is similar to the bulk except the lower conduction band intensity, in accord with recent experiments. Whereas, as a result of bridging-oxygen vacancy, the atom relaxations exchanged and reconstruction occur. The 2 excess electrons left behind removal of one bridge O atom are localized on the Ti-t2g conduction band orbitals, convert some of the Ti4+ ions into Ti3+ ions and result a compensatory shift in the Fermi level. The band gaps we calculated for stoichiometric surface is similar to the bulk, but its increase can be found for Ob vacancy surface.
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Бекенев, В. Л., and С. М. Зубкова. "Атомная и электронная структура реконструкций поверхности (111) в кристаллах ZnSe и CdSe." Физика твердого тела 60, no. 1 (2018): 187. http://dx.doi.org/10.21883/ftt.2018.01.45308.136.
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AbstractThe atomic and electron structure of four variants of polar (111)-(2 × 2) surfaces in ZnSe and CdSe terminated by a cation, namely, the ideal, relaxed, reconstructed, and relaxed after reconstruction surfaces, are calculated for the first time from the first principles. The surface is simulated by a film with a thickness of 12 atomic layers and a vacuum gap of ~16 Å in the layered superlattice approximation. Four fictitious hydrogen atoms with a charge of 0.5 electrons each are added for closing dangling Se bonds on the opposite side of the film. Ab initio calculations are performed using the QUANTUM ESPRESSO software based on the density functional theory. It is shown that relaxation results in splitting of atomic layers. We calculate and analyze the band structures and total and layer-wise densities of electron states for four variants of the surface.
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McGhee, Joseph, and Vihar P. Georgiev. "Simulation Study of Surface Transfer Doping of Hydrogenated Diamond by MoO3 and V2O5 Metal Oxides." Micromachines 11, no. 4 (April 20, 2020): 433. http://dx.doi.org/10.3390/mi11040433.
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In this work, we investigate the surface transfer doping process that is induced between hydrogen-terminated (100) diamond and the metal oxides, MoO3 and V2O5, through simulation using a semi-empirical Density Functional Theory (DFT) method. DFT was used to calculate the band structure and charge transfer process between these oxide materials and hydrogen terminated diamond. Analysis of the band structures, density of states, Mulliken charges, adsorption energies and position of the Valence Band Minima (VBM) and Conduction Band Minima (CBM) energy levels shows that both oxides act as electron acceptors and inject holes into the diamond structure. Hence, those metal oxides can be described as p-type doping materials for the diamond. Additionally, our work suggests that by depositing appropriate metal oxides in an oxygen rich atmosphere or using metal oxides with high stochiometric ration between oxygen and metal atoms could lead to an increase of the charge transfer between the diamond and oxide, leading to enhanced surface transfer doping.
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Demarina, N., and D. Grutzmacher. "Influence of Surface States on Electronic Band Structure and Electron Density in InAs Nanowires and InAs Shell Nanowires." ECS Transactions 64, no. 8 (August 9, 2014): 95–99. http://dx.doi.org/10.1149/06408.0095ecst.
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Liu, Hong Ge, Rui Jun Zhang, Hong Yan Jin, and Qiu Xiang Liu. "First Principles Study of Surface Properties for Silicon Carbide-Derived Structures." Advanced Materials Research 433-440 (January 2012): 306–12. http://dx.doi.org/10.4028/www.scientific.net/amr.433-440.306.
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Using first-principles ultra-soft pseudo-potential approach of the plane wave based on the density functional theory (DFT), we investigated the surface properties for silicon carbide-derived structure (i.e. SiCDS). The calculated results show that, movement of C and Si atoms caused by Si removal results in surface structural changing, and a nanoporous surface feature can be observed on the SiCDS surfaces when more Si atoms are removed. The mulliken population analysis indicates that the Si removal leads to the stronger chemical bonds between C–Si and the formation of new stronger chemical bands between C–C. From the density of states, as the Si removal proportion increases, C2p becomes gradually dominant in the SiCDS surface state electrons. Moreover, the Si removal leads to evidently different band gaps, indicating that the conductivity for SiCDS surface structures can be adjusted through the Si removal.
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Roslyak, Oleksiy, Godfrey Gumbs, and Danhong Huang. "Graphene nanoribbons in criss-crossed electric and magnetic fields." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368, no. 1932 (December 13, 2010): 5431–43. http://dx.doi.org/10.1098/rsta.2010.0215.
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Graphene nanoribbons (GNRs) in mutually perpendicular electric and magnetic fields are shown to exhibit dramatic changes in their band structure and electron-transport properties. A strong electric field across the ribbon induces multiple chiral Dirac points, closing the semiconducting gap in armchair GNRs. A perpendicular magnetic field induces partially formed Landau levels as well as dispersive surface-bound states. Each of the applied fields on its own preserves the even symmetry E k = E − k of the sub-band dispersion. When applied together, they reverse the dispersion parity to be odd, which gives E e, k =− E h,− k , and mix the electron and hole sub-bands within the energy range corresponding to the change in potential across the ribbon. This leads to oscillations of the ballistic conductance within this energy range. The broken time-reversal symmetry provides dichroism in the absorption of the circularly polarized light. As a consequence, one can observe electrically enhanced Faraday rotation, since the edges of the ribbon provide formation of the substantial density of states.
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Князев, Ю. В., А. В. Лукоянов, and Ю. И. Кузьмин. "Электронная структура соединения DyFe-=SUB=-2-=/SUB=-Si-=SUB=-2-=/SUB=-: зонный расчет и оптические исследования." Физика твердого тела 62, no. 3 (2020): 364. http://dx.doi.org/10.21883/ftt.2020.03.48997.632.
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Investigations of electronic structure and optical properties of DyFe2Si2 compound have been carried out. Calculations of the band structure were made with employing local electron density approximation with correction for strong electron correlation effects in the 4f-shells of rare earth metal (GGA+U method). Optical properties were studied by ellipsometric technique in wide wavelength interval. A number of spectral and electronic characteristics were determined. It is shown that the optical conductivity of the compound in interband transitions range is interpreted satisfactorily by means of the density of states calculations.
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Quaino, P., E. Santos, G. Soldano, and W. Schmickler. "Recent Progress in Hydrogen Electrocatalysis." Advances in Physical Chemistry 2011 (June 4, 2011): 1–14. http://dx.doi.org/10.1155/2011/851640.
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Recently, we have proposed a unified model for electrochemical electron transfer reactions which explicitly accounts for the electronic structure of the electrode. It provides a framework describing the whole course of bond-breaking electron transfer, which explains catalytic effects caused by the presence of surface d bands. In application on real systems, the parameters of this model—interaction strengths, densities of states, and energies of reorganization—are obtained from density functional theory (DFT). In this opportunity, we review our main achievements in applying the theory of electrocatalysis. Particularly, we have focused on the electrochemical adsorption of a proton from the solution—the Volmer reaction—on a variety of systems of technological interest, such as bare single crystals and nanostructured surfaces. We discuss in detail the interaction of the surface metal d band with the valence orbital of the reactant and its effect on the catalytic activity as well as other aspects that influence the surface-electrode reactivity such as strain and chemical factors.
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Chettri, B., P. K. Patra, Sunita Srivastava, Lalhriatzuala, Lalthakimi Zadeng, and D. P. Rai. "Electronic Properties of Hydrogenated Hexagonal Boron Nitride (h-BN): DFT Study." Senhri Journal of Multidisciplinary Studies 4, no. 2 (December 28, 2019): 72–79. http://dx.doi.org/10.36110/sjms.2019.04.02.008.
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In this work, we have constructed the hydrogenated hexagonal boron nitride (h-BN) by placing hydrogen atom at different surface sites. The possibility of hydrogen adsorption on the BN surface has been estimated by calculating the adsorption energy. The electronic properties were calculated for different hydrogenated BNs. The theoretical calculation was based on the Density Functional Theory (DFT). The electron-exchange energy was treated within the most conventional functional called generalized gradient approximation. The calculated band gap of pure BN is 3.80 eV. The adsorption of two H-atoms at two symmetrical sites of B and N sites reduces the band gap value to 3.5 eV. However, in all other combination the systems show dispersed band at the Fermi level exhibiting conducting behavior. Moreover, from the analysis of band structure and Density Of States we can conclude that, the hydrogenation tunes the band gap of hexagonal boron nitride.
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RAJ, SATYABRATA, TAKAFUMI SATO, SEIGO SOUMA, TAKASHI TAKAHASHI, D. D. SARMA, and PRIYA MAHADEVAN. "METAL-INSULATOR TRANSITION OF NaxWO3 STUDIED BY ANGLE-RESOLVED PHOTOEMISSION SPECTROSCOPY." Modern Physics Letters B 23, no. 24 (September 20, 2009): 2819–46. http://dx.doi.org/10.1142/s0217984909021004.
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The electronic structure of sodium tungsten bronzes Na x WO 3 is investigated by high-resolution angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra measured in both insulating and metallic phases of Na x WO 3 reveals the origin of metal-insulator transition (MIT) in sodium tungsten bronze system. It is found that in insulating Na x WO 3 the states near the Fermi level (EF) are localized due to the strong disorder caused by the random distribution of Na + ions in WO 3 lattice. Due to the presence of disorder and long-range Coulomb interaction of conduction electrons, a soft Coulomb gap arises, where the density of states vanishes exactly at EF. In the metallic regime the states near EF are populated and the Fermi level shifts upward rigidly with increasing electron doping (x). Volume of electron-like Fermi surface (FS) at the Γ(X) point of the Brillouin zone gradually increases with increasing Na concentration due to W 5d t2g band filling. A rigid shift of the Fermi energy is found to give a qualitatively good description of the Fermi surface evolution. As we move from bulk-sensitive to more surface sensitive photon energy, we found the emergence of Fermi surfaces at X(M) and M(R) points similar to the one at the Γ(X) point in the metallic regime, suggesting that the reconstruction of surface was due to rotation/deformation of WO 6 octahedra.
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Campet, G., J. P. Manaud, C. Puprichitkun, Z. W. Sun, and P. Salvador. "Protection of Photoanodes Against Photo-Corrosion by Surface Deposition of Oxide Films: Criteria for Choosing the Protective Coating." Active and Passive Electronic Components 13, no. 3 (1989): 175–89. http://dx.doi.org/10.1155/1989/78914.
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Two strategies to solve the problem of instability of photoanodes against photocorrosion have been explored. The photocorrosion of photoanodes generally occurs when they enter the fabrication of efficient photoelectrochemical cells (i.e. showing high values of the open circuit voltage and photocurrent density).One of these strategies consists of protecting the photoanode against photocorrosion by a non-conducting oxide film deposited on its surface. The oxide must have a cationic valence band, or valence energy states, falling either above, or at the same level as, the top of the valence band of the anode. The significant photocurrent observed with the n-GaAs/Sr0.98Na0.01Ce0.01TiO3hybridelectrode structure confirms the validity of the model.The second possibility deals with the protection of the photoanode by a conducting oxide film in which the carrier transport occurs, close to the Fermi level, via either a partially filled band or a sufficiently high density of localized states. We have illustrated this method of protection by depositing n-SrTiO3on n-GaAs. The n-SrTiO3films have the Fermi level pinned within the forbidden band by Ti:3d(t2g) energy states. The corresponding electrochemical cells exhibit photoconversion efficiency as high as 18% for an illumination of 5 mW/cm2.
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Заводинский, В. Г., and А. П. Кузьменко. "Электронные состояния наносистем на основе сульфида кадмия в форме сфалерита." Физика и техника полупроводников 53, no. 10 (2019): 1419. http://dx.doi.org/10.21883/ftp.2019.10.48300.9092.
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The electronic structure of nanosystems on the basis of cadmium sulfide in a blende phase (zb-CdS) is investigated using the method of the density functional theory and pseudo-potentials. It is shown that the used approach allows to describe electronic states of this material rather correctly. It is revealed that the surface (100) - zb-CdS is characterized by the metal-like density of electronic states while the surfaces (110) - zb-CdS has a forbidden band at the Fermi level, and nanofilms with this orientation can be used as material for semiconductor devices. Epitaxial layered nanosystems (110) - zb-CdS-Si also show semiconductor properties.
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DRECHSLER, S. L., G. PAASCH, J. MÁLEK, S. V. SHULGA, H. ESCHRIG, and H. ROSNER. "THEORETICAL ASPECTS OF THE FIELD INDUCED SUPERCONDUCTIVITY IN POLYACENES AND C60." International Journal of Modern Physics B 16, no. 11n12 (May 20, 2002): 1547–51. http://dx.doi.org/10.1142/s0217979202011299.
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The electronic structure and the superconductivity in field-doped polyacenes are considered. Within a modified Thomas–Fermi approach for typical experimental values of the surface charge density the injected charge is confined to a monolayer. The electron–phonon coupling constant for internal modes λintra is estimated using the work of Devos and Lanoo (Ref. 4) and the density of states N(0) estimated from a 2D tight-binding model derived from a full potential LDA band structure calculation for bulk anthracene. The empirical values of the Coulomb pseudopotentials are significantly enhanced. The strong Coulomb interaction is considered as a key quantity which determines the large differences in the critical temperatures achieved for n-doped polyacenes and C 60.
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Elegbeleye, Ife Fortunate, Nnditshedzeni Eric Maluta, and Rapela Regina Maphanga. "Density Functional Theory Study of Optical and Electronic Properties of (TiO2)n=5,8,68 Clusters for Application in Solar Cells." Molecules 26, no. 4 (February 11, 2021): 955. http://dx.doi.org/10.3390/molecules26040955.
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A range of solution-processed organic and hybrid organic−inorganic solar cells, such as dye-sensitized and bulk heterojunction organic solar cells have been intensely developed recently. TiO2 is widely employed as electron transporting material in nanostructured TiO2 perovskite-sensitized solar cells and semiconductor in dye-sensitized solar cells. Understanding the optical and electronic mechanisms that govern charge separation, transport and recombination in these devices will enhance their current conversion efficiencies under illumination to sunlight. In this work, density functional theory with Perdew-Burke Ernzerhof (PBE) functional approach was used to explore the optical and electronic properties of three modeled TiO2 brookite clusters, (TiO2)n=5,8,68. The simulated optical absorption spectra for (TiO2)5 and (TiO2)8 clusters show excitation around 200–400 nm, with (TiO2)8 cluster showing higher absorbance than the corresponding (TiO2)5 cluster. The density of states and the projected density of states of the clusters were computed using Grid-base Projector Augmented Wave (GPAW) and PBE exchange correlation functional in a bid to further understand their electronic structure. The density of states spectra reveal surface valence and conduction bands separated by a band gap of 1.10, 2.31, and 1.37 eV for (TiO2)5, (TiO2)8, and (TiO2)68 clusters, respectively. Adsorption of croconate dyes onto the cluster shifted the absorption peaks to higher wavelengths.
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Riech, I., M. Acosta, M. A. Zambrano-Arjona, F. Peñuñuri, M. Rosado-Mendoza, E. Marín, P. Rodríguez-Fragoso, and J. G. Mendoza-Álvarez. "Physical Properties of Macroporous Tungsten Oxide Thin Films and Their Impact on the Photocurrent Density." International Journal of Photoenergy 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/765297.
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Tungsten trioxide (WO3) films were prepared using polystyrene spheres of two different diameters as a template in order to create porous layers. X-ray diffraction data and electron microscopy images show that annealed films exhibit polycrystalline structure with monoclinic phase and pore size of approximately hundred nanometers. The optical band gap energies have been determined by photoacoustic spectroscopy as 3.17 eV, and this value was not affected by sample morphology. Low temperature photoluminescence spectra exhibit broad band in the blue region. Deconvolutions of PL spectra show that there are two transitions which intensity depends on thin film pore size. We discuss the possible origin of this emissions associated with oxygen vacancies and surface states. A comparative study of the WO3films used as photoanodes is presented and correlated with PL results.
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Gernhart, Zane C., Juan A. Colón Santana, Lu Wang, Wai-Ning Mei, and Chin Li Cheung. "Photoelectron Spectroscopy Characterization and Computational Modeling of Gadolinium Nitride Thin Films Synthesized by Chemical Vapor Deposition." MRS Proceedings 1729 (2015): 131–36. http://dx.doi.org/10.1557/opl.2015.193.
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ABSTRACTHere we report our study of the electronic properties of [100]-textured gadolinium nitride (GdN) thin films synthesized using a chemical vapor deposition (CVD) method. The electronic properties of the films were investigated using photoemission and inverse photoemission spectroscopy coupled with computational modeling. Our density functional theory (DFT) calculations suggest that the theoretically predicted half-metallic electronic structure of GdN is likely due to its low density of states (DOS) at the Fermi level. These calculations are supported by our photoemission and inverse photoemission spectroscopic measurements which show a band gap for the prepared films of a few milli-electron volts, seemingly consistent with the predicted electronic structure. Additionally, the use of a CVD gallium nitride capping layer was found to decelerate the surface oxidation of our GdN samples.
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Князев, Ю. В., А. В. Лукоянов, Ю. И. Кузьмин, S. Gupta, and K. G. Suresh. "Электронные и спектральные свойства интерметаллических соединений RRhSn (R=Gd, Tb)." Физика твердого тела 60, no. 2 (2018): 222. http://dx.doi.org/10.21883/ftt.2018.02.45371.218.
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AbstractThe investigations of electronic structure and optical properties of GdRhSn and TbRhSn were carried out. The calculations of band spectrum, taking into account the spin polarization, were performed in a local electron density approximation with a correction for strong correlation effects in 4f shell of rare earth metal (LSDA + U method). The optical studies were done by ellipsometry in a wide range of wavelengths, and the set of spectral and electronic characteristics was determined. It was shown that optical absorption in a region of interband transitions has a satisfactory explanation within a scope of calculations of density of electronic states carried out.
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Gao, Hongtao, Bing Lu, Fangfang Liu, Yuanyuan Liu, and Xian Zhao. "Photocatalytical Properties and Theoretical Analysis of N, Cd-Codoped TiO2Synthesized by Thermal Decomposition Method." International Journal of Photoenergy 2012 (2012): 1–9. http://dx.doi.org/10.1155/2012/453018.
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N, Cd-codoped TiO2have been synthesized by thermal decomposition method. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-visible diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) specific surface area analysis, respectively. The products represented good performance in photocatalytic degradation of methyl orange. The effect of the incorporation of N and Cd on electronic structure and optical properties of TiO2was studied by first-principle calculations on the basis of density functional theory (DFT). The impurity states, introduced by N 2p or Cd 5d, lied between the valence band and the conduction band. Due to dopants, the band gap of N, Cd-codoped TiO2became narrow. The electronic transition from the valence band to conduction band became easy, which could account for the observed photocatalytic performance of N, Cd-codoped TiO2. The theoretical analysis might provide a probable reference for the experimentally element-doped TiO2synthesis.
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Lu, Jibao, Hao Jin, Ying Dai, Kesong Yang, and Baibiao Huang. "Effect of Electronegativity and Charge Balance on the Visible-Light-Responsive Photocatalytic Activity of Nonmetal Doped Anatase TiO2." International Journal of Photoenergy 2012 (2012): 1–8. http://dx.doi.org/10.1155/2012/928503.
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The origin of visible light absorption and photocatalytic activity of nonmetal doped anatase TiO2were investigated in details in this work based on density functional theory calculations. Our results indicate that the electronegativity is of great significance in the band structures, which determines the relative positions of impurity states induced by the doping species, and further influences the optical absorption and photocatalytic activities of doped TiO2. The effect of charge balance on the electronic structure was also discussed, and it was found that the charge-balance structures may be more efficient for visible light photocatalytic activities. In addition, the edge positions of conduction band and valence band, which determine the ability of a semiconductor to transfer photoexcited electrons to species adsorbed on its surface, were predicted as well. The results may provide a reference to further experimental studies.
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Wang, Jingqin, Jianyu Yang, Yancai Zhu, Guangzhi Zhang, Delin Hu, and Guanglin Huang. "Effect of Ni, N Co-Doped on Properties of AgSnO2 Contact Materials." Crystals 11, no. 6 (June 20, 2021): 707. http://dx.doi.org/10.3390/cryst11060707.
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The first-principles method based on density functional theory was used to analyze the impurity formation energies, energy bands, density of states, electron overlap population and elastic modulus of SnO2, SnO2–Ni, SnO2–N and SnO2–Ni–N. SnO2 powders with different additives were prepared by the sol-gel method, and then X-ray diffraction experiments and wettability experiments were carried out. The powder metallurgy method was used to prepare AgSnO2 contacts with different additives. The simulation experiments on hardness, electrical conductivity and electrical contact were carried out. The simulation results show that the conductivity of Ni–N co-doped SnO2 is best, and more impurity levels are introduced into the forbidden band, thereby increasing the carrier concentration, reducing the band gap, and improving the conductivity. The experimental results show that Ni, N doping does not change the structure of SnO2, so doped SnO2 still belongs to the tetragonal system. Ni–N co-doping can better improve the wettability between SnO2 and Ag, reduce the accumulation of SnO2 on the contact surface and reduce the contact resistance. Ni–N co-doped SnO2 has the smallest hardness, improving ductility, molding and service life of the AgSnO2 contact material.
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Mebrek, M., M. Berber, B. Doumi, and A. Mokaddem. "First-principles study of the structural, electronic, and elastic properties of Sc2SiX (X=C, N)." Revista Mexicana de Física 67, no. 3 May-Jun (April 30, 2021): 500. http://dx.doi.org/10.31349/revmexfis.67.500.
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Using ab-initio calculations, we studied the structural, elastic, and electronic properties of Sc2SiX compounds with, (X=C, N). The negative formation energy and the positive cohesive energy indicate that these compounds are energetically stable and can be synthesized in normal conditions. Sc2SiC and Sc2SiN compounds are mechanically stable, estimated by the individual elastic constants. Elastic constants and modulus increase when C is substituted by N. The elastic anisotropy in Sc2SiC is high compared to Sc2SiN. Both nanolaminates are fragile in nature. Sc2SiC is more conductive than Sc2SiN. The calculated electron band structures and the density of states imply that the chemical bond in two compounds is a combination of covalent, ionic, and metallic nature. The main factors governing the electronic properties are the hybrid states Sc- 3d, Si-3p, and C -2p and the bond (p-d) stabilizes the structure. Fermi's surface characteristics have been studied for the first time, which are changed when replacing N by C. Based on the estimate of the total energy, we conclude that the replacement of C by N will lead to a stabilization of the hexagonal structure and a decrease of the metallic support.
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Лукоянов, А. В., Ю. В. Князев, and Ю. И. Кузьмин. "Электронная структура интерметаллического соединения GdCuGe." Физика твердого тела 60, no. 4 (2018): 627. http://dx.doi.org/10.21883/ftt.2018.04.45667.288.
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AbstractThe electronic structure of GdCuGe intermetallic compound has been studied. Spin-polarized energy spectrum calculations have been performed by the band method with allowance for strong electron correlations in the 4 f -shell of gadolinium ions. Antiferromagnetic ordering of GdCuGe at low temperatures has been obtained in a theoretical calculation, with the value of the effective magnetic moment of gadolinium ions reproduced in fair agreement with experimental data. The electronic density of states has been analyzed. An optical conductivity spectrum has been calculated for GdCuGe; it reveals specific features that are analogous to the ones discovered previously in the GdCuSi compound with a similar hexagonal structure.
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Alnarabiji, Mohamad Sahban, Noorhana Yahya, Sharifah Bee Abdul Hamid, Khairun Azizi Azizli, Muhammad Kashif, Saima Qureshi, and Bilal Alqasem. "The Role of Surface Area of ZnO Nanoparticles as an Agent for some Chemical Reactions." Defect and Diffusion Forum 354 (June 2014): 201–13. http://dx.doi.org/10.4028/www.scientific.net/ddf.354.201.
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Synthesising zinc oxide nanoparticles (ZnO-NPs) to get certain characteristics to be applied in Enhanced Oil Recovery (EOR) is still challenging to date. In this work, the importance of high surface area of ZnO nanoparticles as EOR agent was highlighted. A simulation on density of state (DOS), band structure and adsorption energy of hydrogen and nitrogen gases on the surface of ZnO was carried out; it is observed that from the band structure of the band gap value for ZnO is 0.808ev. For the ZnO, Zn 4s states contribute to conduction band and O 2p states contribute to valence band. ZnO-NPs were synthesised using the sol-gel method by dissolving zinc nitrate hexahydrate in nitric acid and varying the stirring time (1 and 24h) and sintering time (30 and 40 min). A microwave oven was used for annealing ZnO without insulating the samples in any casket. The results show that 30 and 40 min of annealing and stirring for 1 & 24 h influenced the morphology and size of ZnO-NPs. These parameters could be tailored to generate a range of nanoparticle morphology (flask and/with agglomerated nanoparticles in a corn shape) obtained by Field Emission Scanning Electron Microscope (FESEM) and hexagonal crystal, determined by X-ray diffractometer (XRD), with the mean size of 70.5 & 74.9 nm and a main growth at the peak (101). The prepared sample via stirring for 24h and sintering for 40 min was chosen to prepare ZnO nanofluid because it has the highest surface area (BET) among the rest of samples, 0.23 m2/g. 10% of Original Oil In Place (OOIP) was recovered successfully to prove that ZnO is a good candidate to be applied in some chemical reactions. Moreover, it was found that ZnO is a promising catalyst for ammonia synthesis based on the adsorption energy of hydrogen and nitrogen gases (-1.05 and-1.60 kcal/mol respectively).
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Князев, Ю. В., А. В. Лукоянов, Ю. И. Кузьмин, and M. Vasundhara. "Структура электронных состояний в FeSb-=SUB=-2-=/SUB=- по данным оптической спектроскопии и зонных расчетов." Физика твердого тела 61, no. 6 (2019): 1047. http://dx.doi.org/10.21883/ftt.2019.06.47677.374.
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The electronic structure and optical properties of the binary intermetallic compound FeSb2 have been studied. The band structure was calculated in the local density approximation, which showed the existence of a narrow ~0.3 eV gap in the energy spectrum of this material. The spectral characteristics were studied by ellipsometric method in the wavelength range of 0.22-18 μm. It is shown that the experimental optical conductivity of the compound in the region of interband transitions is satisfactorily interpreted in the framework of the calculations of the density of electronic states. The work was performed as part of the state assignment of the Ministry of Education and Science of the Russian Federation (theme Electron, N AAAA-A18-118020190098-5) with partial support from the Russian Foundation for Basic Research (project N 17-52-45056).
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Pakdel, Sahar, Mahdi Pourfath, and J. J. Palacios. "An implementation of spin–orbit coupling for band structure calculations with Gaussian basis sets: Two-dimensional topological crystals of Sb and Bi." Beilstein Journal of Nanotechnology 9 (March 28, 2018): 1015–23. http://dx.doi.org/10.3762/bjnano.9.94.
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We present an implementation of spin–orbit coupling (SOC) for density functional theory band structure calculations that makes use of Gaussian basis sets. It is based on the explicit evaluation of SOC matrix elements, both the radial and angular parts. For all-electron basis sets, where the full nodal structure is present in the basis elements, the results are in good agreement with well-established implementations such as VASP. For more practical pseudopotential basis sets, which lack nodal structure, an ad-hoc increase of the effective nuclear potential helps to capture all relevant band structure variations induced by SOC. In this work, the non-relativistic or scalar-relativistic Kohn–Sham Hamiltonian is obtained from the CRYSTAL code and the SOC term is added a posteriori. As an example, we apply this method to the Bi(111) monolayer, a paradigmatic 2D topological insulator, and to mono- and multilayer Sb(111) (also known as antimonene), the former being a trivial semiconductor and the latter a topological semimetal featuring topologically protected surface states.
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Liu, Fang, Hao Zheng, Tianze Jiang, Bin Liu, Jianming Zhang, Hang Yuan, Fengcheng Liu, Xiaoxue Fan, and Xiaoping Ouyang. "Effect of H2O Molecule Adsorption on the Electronic Structure and Optical Properties of the CsI(Na) Crystal." Materials 14, no. 7 (March 31, 2021): 1720. http://dx.doi.org/10.3390/ma14071720.
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We investigated H2O molecule adsorption that had an effect on the luminescence properties of the CsI(Na) crystal using experiments and first-principle calculations. We measured the emission spectra of the CsI(Na) crystal at different exposure times under gamma ray excitation. The experimental results showed that the energy resolution of the CsI(Na) crystal was worse when the crystal surface adsorbed more H2O molecules, and the crystal surface deliquescence decreased the luminescence efficiency of the CsI(Na) crystal. We studied the band structure, density of states, and optical properties changes caused by H2O molecule adsorption on the CsI(Na) (010) surface. The generalized gradient approximation (GGA) was used to describe the exchange and correlation potential between the electrons. Our calculation results showed that the band gap width of the CsI(Na) (010) surface decreased after adsorbing H2O molecules, while three new peaks appeared in the valence band, and the absorption coefficient decreased from 90,000 cm−1 to 65,000 cm−1, and the reflection coefficient decreased from 0.195 to 0.105. Further, the absorption coefficient was reduced by at least 25% because of H2O molecule adsorption, which led to the luminescence degradation of the CsI(Na) crystal.
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Jena, Soumyasree, and Sanjoy Datta. "Role of Exchange-Correlation Functional in Bulk Bismuth." Materials Science Forum 978 (February 2020): 446–53. http://dx.doi.org/10.4028/www.scientific.net/msf.978.446.
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Presence of Bismuth (Bi) leads to topologically nontrivial band structure in many materials, especially in topological insulators. Traditionally Bi is known to be a semimetal but, quite surprisingly, in a recent experiment bulk Bi has been found to be a superconductor below 0.53 mK at ambient pressure. In order to have a closer look at the electronic properties of bulk Bi in the wake of this unexpected experimental evidence of superconducting phase, we have performed density-functional-theory (DFT) based first principle calculations using plane-wave basis set and with suitable ionic pseudopotentials. We have computed the band structure, density of states and Fermi surfaces for two different type of exchange-correlation (XC) functionals, namely Perdew-Zunger (PZ) and Perdew-Burke-Ernzerhof (PBE) type. Each of these XC functional has been considered without and with spin orbit (SO) interaction. After carefully examining the energy-convergence with respect to plane wave basis set and k-points in each case, the band structure has been calculated along the path Γ-L-T-Γ. Without SO coupling, electron pocket is found near ‘L’ and exactly at ‘Г’ and hole pocket is at ‘T’ for PZ type XC functional, while in the case of PBE-type electron pocket is found exactly at ‘L’ but the hole pocket to be near to ‘T’. With SO coupling, in PZ-type, electron pocket remains at same position, but hole pocket appears only at ‘Г’ point. Finally, when SO coupling is taken into account along with PBE-type XC functional electrons and holes are found at ‘L’ and at ‘T’ respectively. Furthermore, in this case we also observe an increase in the number of holes at ‘T’.
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Юнусов, М. Б., Р. М. Хуснутдинов, and А. В. Мокшин. "Электронные и теплофизические свойства газовых гидратов: результаты моделирования из первых принципов." Физика твердого тела 63, no. 2 (2021): 308. http://dx.doi.org/10.21883/ftt.2021.02.50485.203.
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The results of an ab-initio molecular dynamics study of the electronic and thermophysical properties of methane hydrate with a cubic sI structure are presented. Good agreement of the simulation results for heat capacity at constant volume and density with experimental data is found. Based on the analysis of the density of electronic states, the temperature dependences of the electronic properties of methane hydrate, including the Fermi energy level, width and boundaries of the band gap are determined. For the empty framework of the hydrate (water clathrate framework), the electron energy spectra E(k) were calculated along the directions M-X, X-G, G-M, and G-R. It was found that the presence of CH4 molecules in an aqueous clathrate leads to an increase in the Fermi energy of the hydrate from 2.4 to 3.0 eV.
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Комолов, А. С., Э. Ф. Лазнева, Н. Б. Герасимова, Ю. А. Панина, А. В. Барамыгин, Г. Д. Зашихин, and С. А. Пшеничнюк. "Плотность электронных состояний в зоне проводимости сверхтонких пленок дикарбоксильно замещенного и тетракарбоксильно замещенного нафталина на поверхности окисленного кремния." Физика твердого тела 60, no. 4 (2018): 799. http://dx.doi.org/10.21883/ftt.2018.04.45696.281.
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AbstractThe results of examination of the electronic structure of the conduction band of naphthalenedicarboxylic anhydride (NDCA) films in the process of their deposition on the surface of oxidized silicon are presented. These results were obtained using total current spectroscopy (TCS) in the energy range from 5 to 20 eV above the Fermi level. The energy position of the primary maxima of the density of unoccupied states (DOUS) of an NDCA film was determined based on the experimental TCS data and calculated data and compared with the position of the DOUS maxima of a naphthalenetetracarboxylic dianhydride (NTCDA) film. The theoretical analysis involved calculating the energies and the spatial distribution of orbitals of the molecules under study at the B3LYP/6-31G(d) DFT (density functional theory) level and correcting the obtained energies in accordance with the procedure that was proven effective in earlier studies of the conduction band of films of small conjugated organic molecules. It was found that the DOUS maxima of the NTCDA film in the studied energy interval from 5 to 20 eV above the Fermi level are shifted toward lower electron energies by 1–2 eV relative to the corresponding DOUS maxima of the NDCA film Subdivision of the Ufa Federal Research Centre of the .
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Long, Jin-Ping, Zhou Wan, Xin-Guo Yan, Wei-Qing Huang, Gui-Fang Huang, and Ping Peng. "Band gap engineering by lanthanide doping in the photocatalyst LaOF: First-principles study." International Journal of Modern Physics B 28, no. 11 (March 26, 2014): 1450069. http://dx.doi.org/10.1142/s0217979214500696.
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Recent experiment [Xie et al., Catal. Commun., 27, 21 (2012)] reported that LaOF is an active catalyst for water reduction: the catalytic activity per surface area of LaOF is about ten times higher than that of anatase TiO 2. First-principles density functional theory (DFT) calculations have been performed on Ln-doped LaOF (Ln = Ce , Pr , Nd and Pm ) to evaluate the effect of lanthanide doping on the electronic and optical properties. It is found that the lowest conduction band (CB) edge potential of LaOF is less than zero (versus normal hydrogen electrode (NHE)), confirming it has enough driving force for photocatalytic water splitting. The band gap of LaOF could be reduced significantly by lanthanide doping. Electronic structure analysis shows that the impurity states appear deep inside the band gap of LaOF, which is in favor of the separation center of photogenerated carriers due to large effective mass differences between electron and hole. Moreover, doping both Pm and Nd into LaOF is an effective approach to extend the optical absorption edge to the visible light. These findings suggest that LaOF doped with lanthanide element is a promising candidate for the photocatalytic hydrogen generation from water and pollutant decomposition.
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Князев, Ю. В., А. В. Лукоянов, Ю. И. Кузьмин, and А. Г. Кучин. "Роль 3d-электронной подсистемы в эволюции зонной структуры, магнитных и оптических свойств соединений ErNi-=SUB=-5-x-=/SUB=-Co-=SUB=-x-=/SUB=- (x=0-4)." Физика твердого тела 61, no. 1 (2019): 5. http://dx.doi.org/10.21883/ftt.2019.01.46888.173.
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AbstractThe evolution of the electronic structure and optical and magnetic properties of ErNi_5 – _ x Co_ x compounds ( x = 0–4), occurring upon substitution of nickel by cobalt atoms, has been investigated. Spin-polarization calculations of the band spectrum of these intermetallic compounds have been performed within the local spin density approximation with a correction for strong electron correlations in the 4 f shell of a rare-earth ion (method LSDA+U). The values of magnetic moments for erbium, nickel, and cobalt ions (located at different crystallographic sites) are obtained. The exchange-interaction parameters for the 3 d sublattice of transition metals are determined. The spectral properties of the compounds have been investigated in the wavelength range of 0.22–15 μm by optical ellipsometry. The experimental frequency dependences of the optical conductivity in the interband absorption region are compared with the corresponding characteristics calculated based on the density of electronic states.
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Hinks, D. G. "The Nature of Superconductivity in Ba1-XKXBiO3." MRS Bulletin 15, no. 6 (June 1990): 55–59. http://dx.doi.org/10.1557/s0883769400059522.
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Superconductivity in potassium-doped BaBiO3 was first observed by Mattheiss et al. in 1988 and the structure of the superconducting material was determined by Cava et al. The material crystallizes in a simple perovskite structure with potassium substituted on the barium site as shown in Figure 1. Unlike the layered copper-oxide materials, this compound is simple cubic and thus isotropic in the superconducting state and shows no magnetism. Band theory calculations show that the electronic structure is simple, with conduction bands composed of Bi(sp)O(p) hybridized orbitals and, unlike the copper-oxide materials, there are no d electrons at the Fermi surface or involved in the superconductivity. Photoemission and inverse-photoemission agree well with the theoretical calculations and show metallic behavior with a low density of states at the Fermi level consisting of Bi-O sp hybrids. This material is structurally and electronically simple compared to the copper-oxide compounds and, therefore, should be much easier to investigate experimentally and understand theoretically. This article discusses recent results concerning the structural properties of the material and describes several experiments that give information on the superconducting state.
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Diao, Xin-Feng, Yan-Lin Tang, Quan Xie, Tian-Yu Tang, Jia Lou, and Li Yuan. "Study on the Properties of Organic–Inorganic Hole Transport Materials in Perovskite Based on First-Principles." Journal of Nanoelectronics and Optoelectronics 14, no. 12 (December 1, 2019): 1786–95. http://dx.doi.org/10.1166/jno.2019.2687.
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Newport Inc. was licensed recently by the National Renewable Energy Laboratory of the United States to update the highest efficiency of the perovskite solar cell (PSC) certification of PSCs by 23.7%. Exploring new hole transfer layer is the key to the future development of PSC. In this paper, we constructed seven organic hole transport material molecules such as copper-phthalocyanine (CuPc), 2',7'-bis(bis(4-methoxyphenyl)amino)spiro[cyclopenta-[2,1-b:3,4-b']dithiophene-4,9'-fluorene] (FDT), Poly-triarylamine (PTAA), poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate) (PEDOT/PSS) poly(3-hexylthiophene) (P3HT) and six in-organic hole transport material molecules such as CuCSN, CuI, InCuS2, CuO, Cu2O, NiO with Material Studio software. By the structure optimization, their energy band, density of state (DOS), HOMO/lowest unoccupied orbit (LUMO) energy level and absorption spectrum were calculated. Furthermore, the HOMO/LUMO electron cloud distribution map of FDT molecule was analyzed in detail. The results show that the electron cloud is closer to the nucleus with the increase of the isopotential surface value. From the absorption spectra, the absorption wavelengths of most inorganic hole transport materials are mainly concentrated at about 200 nm, which is relatively short. But the absorption wavelengths of organic hole transport materials are distributed in long wavelength region, most of them are above 2000 nm. Only the absorption spectra of PTAA, Spiro OMetad and CuPc are in the range of solar spectrum. The HOMO energy levels of seven organic hole transport materials are slightly higher than the values of valence band of CH3NH3PbI3 and NH2CH = NH2PbI3, which are favorable for carrier injection and transport. The band gap of inorganic hole transport materials CuCSN and CuI is wider. From the energy band structure curve, the effective mass of NiO, CuO, Cu2O carriers is smaller, which the carrier transport rate is relatively high. The hole transport material must have high hole mobility and hole conductivity so as to ensure the effective transport of the hole at the interface between the hole transport layer and the perovskite layer.
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Gong, Shi-Jing, Cheng Gong, Yu-Yun Sun, Wen-Yi Tong, Chun-Gang Duan, Jun-Hao Chu, and Xiang Zhang. "Electrically induced 2D half-metallic antiferromagnets and spin field effect transistors." Proceedings of the National Academy of Sciences 115, no. 34 (August 3, 2018): 8511–16. http://dx.doi.org/10.1073/pnas.1715465115.
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Engineering the electronic band structure of material systems enables the unprecedented exploration of new physical properties that are absent in natural or as-synthetic materials. Half metallicity, an intriguing physical property arising from the metallic nature of electrons with singular spin polarization and insulating for oppositely polarized electrons, holds a great potential for a 100% spin-polarized current for high-efficiency spintronics. Conventionally synthesized thin films hardly sustain half metallicity inherited from their 3D counterparts. A fundamental challenge, in systems of reduced dimensions, is the almost inevitable spin-mixed edge or surface states in proximity to the Fermi level. Here, we predict electric field-induced half metallicity in bilayer A-type antiferromagnetic van der Waals crystals (i.e., intralayer ferromagnetism and interlayer antiferromagnetism), by employing density functional theory calculations on vanadium diselenide. Electric fields lift energy levels of the constituent layers in opposite directions, leading to the gradual closure of the gap of singular spin-polarized states and the opening of the gap of the others. We show that a vertical electrical field is a generic and effective way to achieve half metallicity in A-type antiferromagnetic bilayers and realize the spin field effect transistor. The electric field-induced half metallicity represents an appealing route to realize 2D half metals and opens opportunities for nanoscale highly efficient antiferromagnetic spintronics for information processing and storage.
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Kosarev, A., A. Torres, Y. Hernandez, R. Ambrosio, C. Zuniga, T. E. Felter, R. Asomoza, et al. "Silicon-germanium films deposited by low-frequency plasma-enhanced chemical vapor deposition: Effect of H2 and Ar dilution." Journal of Materials Research 21, no. 1 (January 1, 2006): 88–104. http://dx.doi.org/10.1557/jmr.2006.0013.
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We have studied structure and electrical properties of Si1−YGeY:H films deposited by low-frequency plasma-enhanced chemical vapor deposition over the entire composition range from Y = 0 to Y = 1. The deposition rate of the films and their structural and electrical properties were measured for various ratios of the germane/silane feed gases and with and without dilution by Ar and by H2. Structure and composition was studied by Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and Fourier transform infrared (FTIR) spectroscopy. Surface morphology was characterized by atomic force microscopy (AFM). We found that the deposition rate increased with Y, maximizing at Y = 1 without dilution. The relative rate of Ge and Si incorporation is affected by dilution. Hydrogen preferentially bonds to silicon. Hydrogen content decreases for increasing Y. In addition, optical measurements showed that as Y goes for 0 to 1, the Fermi level moves from mid gap to the conduction band edge; i.e., the films become more n-type. No correlation was found between the pre-exponential and the activation energy of conductivity. The behavior of the conductivity γ-factor suggests a local minimum in the density of states at E ≈ 0.33 eV for the films grown with or without H-dilution and E ≈ 0.25 eV for the films with Ar dilution.
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Al-Khabouri, Saja, Salim Al-Harthi, Toru Maekawa, Mohamed E. Elzain, Ashraf Al-Hinai, Ahmed D. Al-Rawas, Abbsher M. Gismelseed, Ali A. Yousif, and Myo Tay Zar Myint. "Free and partially encapsulated manganese ferrite nanoparticles in multiwall carbon nanotubes." Beilstein Journal of Nanotechnology 11 (December 29, 2020): 1891–904. http://dx.doi.org/10.3762/bjnano.11.170.
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Free and partially encapsulated manganese ferrite (MnFe2O4) nanoparticles are synthesized and characterized regarding structure, surface, and electronic and magnetic properties. The preparation method of partially encapsulated manganese ferrite enables the formation of a hybrid nanoparticle/tube system, which exhibits properties of manganese ferrite nanoparticles inside and attached to the external surface of the tubes. The effect of having manganese ferrite nanoparticles inside the tubes is observed as a shift in the X-ray diffraction peaks and as an increase in stress, hyperfine field, and coercivity when compared to free manganese ferrite nanoparticles. On the other hand, a strong charge transfer from the multiwall carbon nanotubes is attributed to the attachment of manganese ferrite nanoparticles outside the tubes, which is detected by a significant decrease in the σ band emission of the ultraviolet photoemission spectroscopy signal. This is followed by an increase in the density of states at the Fermi level of the attached manganese ferrite nanoparticles in comparison to free manganese ferrite nanoparticles, which leads to an enhancement of the metallic properties.
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Ilyas, Bahaa, and Badal Elias. "A first principles study of the phonon anharmonicity, electronic structure and optical characteristics of LaAlO3." International Journal of Computational Physics Series 1, no. 1 (March 1, 2018): 161–80. http://dx.doi.org/10.29167/a1i1p161-180.
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The way elementary excitations work together with their couplings and interact as condensed matter systems is very important when designing optimum energy-conversion devices. We investigated the electronic structure of LaAlO3, and we show that the bandgap insulator of LaAlO3 obtained theoretically by the hybrid functional HSE06 is an indirect 5.649eV that show a very good agreement with experimental data. The lattice constant is obtained exactly as experiment. In thermos-electric materials, the concept of conversion-efficiency (heat to electricity) is improved instantly by suppressing the phonon quasi-particles propagations that are responsible for draft macroscopic thermal transport. The material presented here for thermo-electric conversion-efficiency of cubic perovskite LaAlO3, show that it has an ultralow thermal-conductivity, while the formalism to its strong phonon scattering interactions resides mostly unclear. From the bases of Ab-initio simulations, the 4-dimensional phonon-dispersion surfaces of the cubic perovskite LaAlO3, have been mapped and we found that the origins of the ionic potential an-harmonicity being responsible for the unique behaviour and properties of LaAlO3. It is investigated that these phonon scattering arise solely from the LaAlO3 unstable electronic-structure, with its orbital interactions resulting to lattice instability similar to the ferroelectric instabilities. Our results show a microscopic insight bonding electronic-structure and phonon an-harmonicity in LaAlO3, and provides some new picture the way interactions happen between phonon–electron and phonon–phonon this lead to understand the concept of ultralow thermal-conductivity. Ab-initio calculations was performed on cubic perovskite LaAlO3 to obtain the phonon density of states (DOS) from 50 K to 5000 K, we find that the anharmonic behaviour starts around temperature limits of 500 K. The computed optical spectra were obtained using both the Beth Slapter Equation BSE and compared with the perturbed method using HSE06, optical spectra show that the inter-band transition occur precisely from the O-valence bands to the La-conduction bands throughout the low energy area. The energy-loss spectrum, optical conductivity and reflectivity and the refractive index are computed from first principles by using HSE06 hybrid functional. The optical band gap of material shows about 6.21 eV, which agrees with some cited experimental measurements.
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Salih, Ehab, and Ahmad I. Ayesh. "Enhancing the Sensing Performance of Zigzag Graphene Nanoribbon to Detect NO, NO2, and NH3 Gases." Sensors 20, no. 14 (July 15, 2020): 3932. http://dx.doi.org/10.3390/s20143932.
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In this article, a zigzag graphene nanoribbon (ZGNR)-based sensor was built utilizing the Atomistic ToolKit Virtual NanoLab (ATK-VNL), and used to detect nitric oxide (NO), nitrogen dioxide (NO2), and ammonia (NH3). The successful adsorption of these gases on the surface of the ZGNR was investigated using adsorption energy (Eads), adsorption distance (D), charge transfer (∆Q), density of states (DOS), and band structure. Among the three gases, the ZGNR showed the highest adsorption energy for NO with −0.273 eV, the smallest adsorption distance with 2.88 Å, and the highest charge transfer with −0.104 e. Moreover, the DOS results reflected a significant increase of the density at the Fermi level due to the improvement of ZGNR conductivity as a result of gas adsorption. The surface of ZGNR was then modified with an epoxy group (-O-) once, then with a hydroxyl group (-OH), and finally with both (-O-) and (-OH) groups in order to improve the adsorption capacity of ZGNR. The adsorption parameters of ZGNR were improved significantly after the modification. The highest adsorption energy was found for the case of ZGNR-O-OH-NO2 with −0.953 eV, while the highest charge transfer was found for the case of ZGNR-OH-NO with −0.146 e. Consequently, ZGNR-OH and ZGNR-O-OH can be considered as promising gas sensors for NO and NO2, respectively.
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Awada, Chawki, Goodfriend M. Whyte, Peter O. Offor, Favour U. Whyte, Mohammed Benali Kanoun, Souraya Goumri-Said, Adil Alshoaibi, Azubike B. C. Ekwealor, Malik Maaza, and Fabian I. Ezema. "Synthesis and Studies of Electro-Deposited Yttrium Arsenic Selenide Nanofilms for Opto-Electronic Applications." Nanomaterials 10, no. 8 (August 8, 2020): 1557. http://dx.doi.org/10.3390/nano10081557.
Full textAbstract:
Nanocomposite films grown by incorporating varying concentrations of Yttrium, a d-block rare-earth ion, into the binary chalcogenide Arsenic selenide host matrix is here presented. Films were grown via the wet-chemical electro-deposition technique and characterized for structural, optical, surface morphology, and photoluminescence (PL) properties. The X-ray Diffraction (XRD) result of the host matrix (pristine film) showed films of monoclinic structure with an average grain size of 36.2 nm. The composite films, on the other hand, had both cubic YAs and tetragonal YSe structures with average size within 36.5–46.8 nm. The fairly homogeneous nano-sized films are shown by the Scanning Electron Microscopy (SEM) micrographs while the two phases of the composite films present in the XRD patterns were confirmed by the Raman shifts due to the cleavage of the As-Se host matrix and formation of new structural units. The refractive index peaked at 2.63 within 350–600 nm. The bandgap energy lies in the range of 3.84–3.95 eV with a slight decrease with increasing Y addition; while the PL spectra depict emission bands across the Vis-NIR spectral regions. Theoretically, the density functional theory (DFT) simulations provided insight into the changes induced in the structure, bonding, and electronic properties. Besides reducing the bandgap of the As2Se3, the yttrium addition has induced a lone pair p-states of Se contributing nearby to Fermi energy level. The optical constants, and structural and electronic features of the films obtained present suitable features of film for IR applications as well as in optoelectronics.
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ANWAR, M., S. A. SIDDIQI, and I. M. GHAURI. "AC CONDUCTION IN MIXED OXIDES Al–In2O3–SnO2–Al STRUCTURE DEPOSITED BY CO-EVAPORATION." Surface Review and Letters 13, no. 04 (August 2006): 457–69. http://dx.doi.org/10.1142/s0218625x06008438.
Full textAbstract:
Conductivity-frequency and capacitance-frequency characteristics of mixed oxides Al – In 2 O 3– SnO 2– Al structure are examined to elicit any correlation with the conduction mechanisms most often observed in thin film work. The existence of Schottky barriers is believed to be due to a strong donor band in the insulator established during the vacuum evaporation when a layer of mixed oxides In 2 O 3– SnO 2 system is sandwiched between two metal electrodes. Low values of activation energy at low temperatures indicate that the transport of the carriers between localized states is mainly due to electronic hopping over the barrier separating the two nearest neighbor sites. The increase in the formation of ionized donors with increase in temperature during electrical measurements indicates that electronic part of the conductivity is higher than the ionic part. The initial increase in conductivity with increase in Sn content in In 2 O 3 lattice is caused by the Sn atom substitution of In atom, giving out one extra electron. The decrease in electrical conductivity above the critical Sn content (10 mol% SnO 2) is caused by the defects formed by Sn atoms, which act as carrier traps rather than electron donors. The increase in electrical conductivity with film thickness is caused by the increase in free carriers density, which is generated by oxygen vacancy acting as two electron donor. The increase in conductivity with substrate and annealing temperatures is due to either the severe deficiency of oxygen, which deteriorates the film properties and reduces the mobility of the carriers or to the diffusion of Sn atoms from interstitial locations into the In cation sites and formation of indium species of lower oxidation state ( In 2+). Calculations of C and σac from tan δ measurements suggest that there is some kind of space-charge polarization in the material, caused by the storage of carriers at the electrodes. Capacitance decreases not only with the rise of frequency but also with the lowering of temperature. At low temperatures the major contribution to capacitance arises from the ionic polarization, however, with the increase of temperature the contribution from orientation polarization would considerably increase. The decrease in capacitance with the increase in frequency may be attributed to interfacial polarization.
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Darvishi, Reza, and Esmaeil Pakizeh. "A Combined Experimental and First-Principle Calculation (DFT Study) for In Situ Polymer Inclusion Membrane-Assisted Growth of Metal-Organic Frameworks (MOFs)." International Journal of Polymer Science 2020 (June 5, 2020): 1–12. http://dx.doi.org/10.1155/2020/1018347.
Full textAbstract:
A simple yet effective strategy was developed to prepare a metal-organic framework- (MOF-) based asymmetric membrane by depositing the Zeolitic imidazolate framework-8 (Zif-8) layer on the aminosilane-functionalized surface of a polymer inclusion membrane via an in situ growth process. During the extraction of the ligand molecules from the source to stripping compartment, metal ions react with ligand, and layers of Zif-8 were gradually grown onto aminosilane-modified polymer inclusion membrane (PIM). The properties of the surface-grown Zif-8 nanocrystalline layer were well characterized by powder X-ray diffraction, adsorption-desorption analysis, and scanning electron microscopy. The potential use of these Zif-8-supported PIM membranes for the separation of gases N2, CH4, and CO2 was evaluated at two temperatures (25 and 50°C) and pressures (1, 3, and 5 bar), by comparing the permeability and selectivity behavior of these membranes with neat PIM. The gas permeability of both pure PIM (PCO2=799.2 barrer) and PIM-co-MOF (PCO2=675.8 barrer) increases with the temperature for all three gases, and the permeation rate order was CO2 > CH4 > N2. The results showed that the presence of a layer of Zif-8 on the surface of the polymer inclusion membranes can get a slightly reduced permeability (~21%) but an enhanced selectivity of up to ~70% for CO2/CH4 and ~34% for CO2/N2. In the case of both membrane types, the ideal permselectivity decreases with the temperature, but this decrease was slightly more pronounced for the case of PIM-co-MOF. To understand more details about the electronic structure and optical and adsorption properties of Zif-8 and M+Zif-8 (M=N2,CH4,and CO2) compounds, the periodic plane-wave density functional theory (DFT) calculations were used. The electronic band structures and density of states for pure Zif-8 showed that this compound is metallic. Also, using DFT, the formation energy of M+Zif-8 compounds was calculated, and we showed that the CO2+Zif-8 composition is more stable than other compounds. This result suggests that the tendency of the Zif-8 compound to absorb the CO2 molecule is higher than that of other molecules. Confirming these results, DFT optical calculations showed that the affinity of the CO2+Zif-8 composition to absorb infrared light was greater than that of the other compounds.
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Басалаев, Ю. М., and А. Б. Гордиенко. "Электронная структура кристаллов Be-IV-P-=SUB=-2-=/SUB=- с решеткой халькопирита." Физика твердого тела 62, no. 11 (2020): 1799. http://dx.doi.org/10.21883/ftt.2020.11.50107.136.
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A group of crystalline compounds of the type Be-IV-P2, (IV = C, Si, Ge, Sn) with a chalcopyrite structure has been studied using the density functional theory methods. The equilibrium parameters of the crystal lattice, band structures, spectra of total and partial densities of states, maps of the charge distribution of valence electrons, tensors of dielectric constant and effective charges, and optical absorption spectra are calculated and obtained.