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This paper presents the results of density functional theory calculations for the (3,1) carbon nanotube ensuing in two structural configurations, representing two local energy minima. To be sure in this conclusion, we used two distinct density functional theory implementations and three different structure optimization algorithms. The interatomic distances of the two kinds of (3,1) carbon nanotubes do not differ too much, but the other properties are more pronounced. We found that the HOMO-LUMO energy gap of the lower energy configuration is 0.69 eV, whereas the second configuration possesses the 0.36 eV HOMO-LUMO gap. Both isomers have been obtained by optimization because the calculations started either with a different initial configuration or with different starting parameters critical for convergence, efficiency and/or accuracy. [ABSTRACT FROM AUTHOR]

In this paper, we report on the deposition of zinc oxide thin films by the plasma enhanced chemical vapor deposition technique. The effects of oxygen flow rate on surface morphology, optic transmission, and gap energy are studied. The X-ray diffraction technique shows polycrystalline phases in the deposited material, the crystal structure is hexagonal, and the preferential orientation of crystal growth is in the (101) direction. The best optical transmission of zinc oxide is of the order of ~ 89%, and a wide optical gap of ~ 3.7 eV. To make a comparison with the present results and theoretical data, an ab initio calculation is carried out by the density functional theory method. To study the oxygen vacancies concentration effect on bandgap and optical transmission, we use three different configurations, namely ZnO0,97, ZnO0,94, and ZnO0,91. To confirm our experimental and calculated results, we compared them to those given in the literature. [ABSTRACT FROM AUTHOR]

In the present paper, inter-ionic reactions involving two cations and four anions were used to model the formation of neutral ion pairs. Moreover, density functional theory technique has been used to describe the physical, chemical, and vibrational properties of the ionic liquids, containing imidazolium-based cations and different anions at functional B3LYP with a def2-SVP basis set. The chemical parameters have been investigated for different ionic liquids along with frontier orbitals "highest occupied molecular orbital" and "lowest unoccupied molecular orbital" studies. All the optimized structures of the ionic liquids did not produce imaginary frequency (i.e., imaginary frequency is zero), which validates that the structures are energetically stable. The density functional theory method provides the stability sequence for ionic liquids: [BMIM][PF6] > [EMIM][PF6] > [BMIM][TFSI] > [EMIM][TFSI] > [EMIM][Cl] > [BMIM][Cl] > [EMIM][Br] > [BMIM][Br]. Herein, [BMIM][PF6] ionic liquid has highest energy gap (4.833 eV) that means that [BMIM][PF6] is the most stable. [ABSTRACT FROM AUTHOR]

Hydrogen bonded liquid crystal mixtures are derived from: (i) non-mesogenic compounds of diglycolic acid (DGA), (ii) mesogenic compounds of 4-amyloxybenzoic acid (5OBA) and (iii) 4-hexyloxy benzoic acid (6OBA). The existence of intermolecular H-bond is confirmed with FTIR and validated using the density functional theory studies. Polarized light microscopy and differential scanning calorimetry are used to observe the phase variations and transition temperature. In addition, enthalpy values of different mesogenic phases are determined. It is worth mentioning that the nematic mesogenic defects with S = ±1 and S = +1=2 are also analyzed. In order to discuss the induced higher order smectic F phase and its stability, the density functional theory study is applied. The band gap energy of the hydrogen bonded liquid crystal mixtures is found to be 5.1780 eV, based on the HUMO-LUMO approach. This induced thermochromic effect of hydrogen bonded liquid crystal mixtures is a useful phenomenon that can be utilized in optical device applications. In this paper, variation on liquid crystal parameters as well as the formation of H-bond between an acceptor and a donor, along with the extension of a chain length, are also reported. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the structural, elastic, electronic, and magnetic properties of Rh2CrGe full-Heusler alloy in the regular type (Cu2MnAl, prototype L21) phase by using the first-principle methods of density functional theory with local spin-density approximation. We have found that Rh2CrGe is stable in the ferromagnetic configuration. This result is confirmed by the calculated cohesive energies. The stability criteria show that Rh2CrGe is mechanically stable in L21 structure. The spin-polarized electronic structures depicted a metallic character. The calculated total magnetic moment of 3.78 μB is not in agreement to the value of 4 μB of the Slater-Pauling rule. Therefore the Rh2CrGe full-Heusler alloy is metallic ferromagnet in nature. [ABSTRACT FROM AUTHOR]

In this paper, we present the first principle calculation of the different properties of the full Heusler compounds Cd2LaB, Cd2PrB, and Cd2CeB. Our calculations are based on density functional theory, using the full potential muffin-tin linear orbital method implemented in the LmtART code. For the determination of the exchange and correlation potential, we used the local density approximation and local spin density approximation. The elastic constants are also calculated. The total magnetic moment of Cd2LaB, Cd2PrB, and Cd2CeB using local spin density approximation are 3.334, 3.482, and 3.473 μB at ambient pressure, respectively. We also present the thermal effects using the quasi-harmonic Debye model, in which the vibrations of the network are taken into account. The effects of temperature and pressure on structural parameters, heat capacity, entropy, coefficient of thermal expansion, and the Debye temperatures are determined for unbalanced Gibbs functions. [ABSTRACT FROM AUTHOR]

The I2-II-IV-VI4 series of quaternary chalcogenides semiconductors have drawn wide interest for their potential application as solar-cell absorbers. In this paper, we present a study of electronic and optical properties of the equilibrium kesterite structure (KS) of Cu2ZnGeS4 (CZGS) calculated by means of the full potential linearized augmented plane wave method. For this purpose, we used the Wien2k code based on the density functional theory with the generalized gradient approximation (GGA), modified Becke-Johnson exchange potential (mBJ) and the Hubbard potential U. The TB-mBJ is used alone or combined with U (TB-mBJ, and TB-mBJ+U). The results are compared with other theoretical results and the available experimental ones. The obtained results show that the top of the valence band is mainly composed by the Cu d orbital while the bottom of the conduction band is a mixture of Ge s and S p states. It was found that KS-CZGS has a direct band gap of 0.3, 1.8 and 2.0 eV using GGA, GGA+TB-mBJ and GGA+TB-mBJ+U, respectively. It is observed that states exist above the Fermi level (0 eV) with a width of 0.3 and 0.2 eV when we use GGA and GGA+TB-mBJ, while these states come down under the Fermi level when using GGA+TB-mBJ+U. The optical properties are calculated and an almost isotropic behavior is found in contrast to the reported properties of the stannite phase. This behavior can be linked to the charge density and the structure. [ABSTRACT FROM AUTHOR]

The paper presents the results of the plane wave density functional theory calculations of newly predicted Y2FeSi full-Heusler alloy with optimized lattice constants. We have explored two most likely structures (AlCu2Mn and CuHg2Ti prototypes) with different atomic arrangements and including collinear magnetic ordering. The results show that the classic L21 structure is more favourable in terms of energy than the second one studied in this work. Moreover, for both crystalline structures ferromagnetic arrangement is more favourable, although in the second structure the difference in energy between ferromagnetic and nonmagnetic state is small. Study did not revealed band gap in any spin channel, yet the spin polarization in majority channel at the Fermi level is significant (σ = 83%). The calculated structural lattice a parameter for the energetically lowest structure is a = 13:0996 a0. For the lattice constant range of 12.2 to 13.2 a0 the total magnetic moment varies significantly from 0.86 μB to 1.74 μB per formula unit. [ABSTRACT FROM AUTHOR]

In this paper, we studied the relaxation of (001) surface of BaTiO3 and SrTiO3 slabs with two termination surfaces and with 3, 5, and 7 layers thickness for each cases, using density functional theory and generalized gradient approximation for exchange-correlation functional and pseudo potential method. We calculated the slab energy and the rate of expansion and contraction of the layers and compare them for different thicknesses. Band structure and density of states for these slabs and for BaTiO3 and SrTiO3 bulk were computed to find out the variation of band gap with respect to slab thickness. It is found that in comparison with bulk, in TiO2 slabs of both materials gap size decreases while in SrO and BaO slabs it increases. [ABSTRACT FROM AUTHOR]

In this paper we investigate fundamental gaps of three octametallic Cr-based molecular rings Cr8F8(Piv)16, Cr7NiF8(Piv)16 and Cr7CdF8(Piv)16 using the SIESTA package. We find that for the ground-state antiferromagnetic configurations, the gap of the homometallic ring is significantly higher than those of the heterometallic rings. In addition, the HOMO and LUMO orbitals are plotted and discussed. [ABSTRACT FROM AUTHOR]

The electronic structures of ε-phase of solid oxygen (O2)4 are studied within the framework of densityfunctional theory. The intriguing molecule has been known to have magnetic properties at room temperature by applying pressure. Nevertheless, until now there was no evidence of band structure studied in the antiferromagnetic behaviour of (O2)4. We report a comparison study for spin and non-spin polarization orbital which suggests that this ferromagnetic configuration of (O2)4 could not be seen experimentally, and antiferromagnetic configuration of (O2)4 was seen at higher pressure of about 10 GPa. The antiferromagnetic state transforms into the superconducting state as the sample temperature decreases. The results can serve as a useful approximation in studying general features of the electronic structure. The (O2)4 clusters are reported in the Raman study, having significant absorption at 1516 cm-1 below infrared region. [ABSTRACT FROM AUTHOR]

In this paper, we studied the relaxation of (001) surface of BaTiO3 and SrTiO3 slabs with two termination surfaces and with 3, 5, and 7 layers thickness for each cases, using density functional theory and generalized gradient approximation for exchange-correlation functional and pseudo potential method. We calculated the slab energy and the rate of expansion and contraction of the layers and compare them for different thicknesses. Band structure and density of states for these slabs and for BaTiO3 and SrTiO3 bulk were computed to find out the variation of band gap with respect to slab thickness. It is found that in comparison with bulk, in TiO2 slabs of both materials gap size decreases while in SrO and BaO slabs it increases. [ABSTRACT FROM AUTHOR]

The theoretical study of the thermoelectric properties of the FeV1-xMnxSb half-Heusler alloy (x = 0, 0.25, 0.5, 0.75, and 1) has been conducted using density functional theory. The aim of this research was to investigate the effect of Mn substitution on the FeVSb system in order to achieve a higher value of ZT. Our findings show that a system with an Mn doping concentration of x = 0:75 achieves the highest values of ZT ~ 0:90 for the spin-down states in the temperature range from 300 to 800 K, making it a promising candidate for future thermoelectric applications. On the other hand, the Mn substitution also triggers the magnetic moment formation and causes a large spin polarization at the Fermi level, leading the system to change from insulator to half-metallic. [ABSTRACT FROM AUTHOR]

Structural properties of CuxLi2-xO (x = 0, 1, 2) system at ambient conditions were presented together with phase transition under high pressure from a cubic cuprite-type (C3) to an antifluorite-type (C1) structure of Cu2O compound (x = 2). The calculations were performed using the full potential linear muffin-tin orbitals approach based on the density functional theory. For the exchange-correlation potential term, we applied the local density approximation. For both the C1 and C3 phases, the lattice constants versus copper concentration (x) were found to deviate slightly from the linear relationship of Vegard's law. It was found that the phase transition from the C3 to the C1 structure for the Cu2O compound occurs at 82 GPa. [ABSTRACT FROM AUTHOR]

In this work, the density functional theory is employed to study the electronic and magnetic properties of Y(Fe,Co,Mn,Ni) doped ZnX (X = S, Se) hexagonal monolayers. The transition metal dopants are substituted in two different positions. The calculated results show that the magnetic properties of the ZnX monolayer can be tuned by changing the kind and distribution of impurities. The Mn and Ni doping does not show polarity and half-metallic property. In the structures doped with Fe and Co, we observed the 100% spin polarity and half-metallic property. Our findings suggest that the doping with the transition metals in this kind of monolayers is a suitable scheme for a future design of transition metal dichalcogenides as a based target in technological applications. [ABSTRACT FROM AUTHOR]

Stacking two sheets of graphene on top of each other and then rotating one of them so that the sheets are slightly misaligned is one of the hot research directions in nanoelectronics. Here, using the density functional theory, we show that the electronic properties of the graphene nanoisland on the graphene substrate are modulated by changing the rotation angle. We observed that the mutual rotation in the range 0-60° contributes to the induction of the van Hove singularity and the quantum oscillation of the density of states at the Fermi level. Our results provide guidance for future experiments targeting the next generation of devices for nanoelectronics and twistronics. [ABSTRACT FROM AUTHOR]

The work is a brief review of the current state of knowledge about high-pressure superconductors with a high value of critical temperature (Tc). The described results relate to hydrogen-rich superconductors with particular emphasis on well-known hydrogen sulfide compounds and also include newly-discovered lanthanum hydride compounds. Since in the considered systems the superconductivity is phononinduced, in theoretical predictions the Eliashberg equations formalism has been used, while some of the results were extended by including the results obtained in calculations using the density functional theory method. Theoretical predictions were compared with the results of experiments available in the literature. A holistic view of the latest results may lead the way to discover the superconductivity at room temperature. [ABSTRACT FROM AUTHOR]

Electronic properties of the LaSb2 superconductor and its non-superconducting LaAgSb2 analogue are determined within the density functional theory approach. The existence of 2D Dirac fermions in the bulk electronic structure of both compounds is unveiled and analysed based on weighted bands calculated around the Fermi level. Interestingly, a lack of superconductivity in LaAgSb2 can be explained in terms of the topological Feshbach shape resonance of some Fermi surface sheets, associated with the reduction of their dimensionality (from 3D to 2D). [ABSTRACT FROM AUTHOR]

An algebraic model of coupled anharmonic oscillators is introduced, capable of describing the stretching vibrations of medium-size molecules. This model is applied to the calculation of O-H vibrational modes of water molecules. In this paper, we have reported the stretching and bending vibrational energy levels of water molecule using the algebraic and density functional theory method. The results obtained by theoretical models show good agreement with the experimental values. [ABSTRACT FROM AUTHOR]

As a three-dimensional (3D) metallic carbon, T14-carbon consisting of interlocking fused hexagons is predicted by first-principles calculations. In this work, an investigation of the structural, elastic, thermodynamic and anisotropic properties of T14-carbon under the pressures of up to 50 GPa is conducted using density functional theory. When the applied pressure increases from 0 GPa to 50 GPa, the elasticconstants, bulk modulus, Young’s modulus and Poisson’s ratio increase while the shear modulus decreases. T14-carbon has dynamic stability and ductility and its thermal conductivity changes slowly with pressure. The anisotropic studies of the bulk modulus, shear modulus, Young’s modulus and other parameters show that T14-carbon exhibits mechanical anisotropy, with maximum and minimum elastic anisotropy in the (100) and (111) planes according to Young’s modulus. [ABSTRACT FROM AUTHOR]

First principle calculations have been performed to investigate the effect of hydrostatic pressure on the electronic structure and optical properties of the narrow band gap InAs compound. The calculations have been done by the full-potential linearized augmented plane wave method, based on the density functional theory utilizing Wien2k package. The exchange-correlation potential is treated by the generalized gradient approximation and a combination of modified Becke-Johnson plus local-density approximation functional. Regarding the electronic structure, using the band structure calculations at different pressures, the pressure dependence of band gap energy is calculated. In the case of optical properties, the effect of hydrostatic pressure on the real and imaginary parts of the dielectric function ε(ω) is calculated. [ABSTRACT FROM AUTHOR]

Nowadays, the uses of nanobiomaterials are increasing and one of the most concerning biomaterial is the hydroxyapatite (HAp). In this study, the electronic properties of the nano hydroxyapatite were studied theoretically using density functional theory. Calculations were carried out on Gaussian 09 package program using the B3LYP functional method, 6-31G(d,p) basis set. We determined the fitting geometry, highest occupied molecular and lowest unoccupied molecular orbital energy, molecular electrostatic potential, electrostatic surface potential, and electronic properties of the nano hydroxyapatite from the calculations. The spectroscopic values of the nano-HAp were also obtained using ab initio computational method. Infrared and Raman spectroscopic data acquired via this method were compared with the literature results. These computational studies on nano hydroxyapatite provide a framework for materials design and selection for biomaterials used in many areas. [ABSTRACT FROM AUTHOR]

We calculate the mirror Chern number (MCN) and the band gap for the alloy Pb1_xSnxSe as a function of the concentration x by using virtual crystalline approximation. We use the electronic structure from the relativistic density functional theory calculations in the Generalized-Gradient-Approximation (GGA) and meta-GGA approximation. Our results obtained with the modified Becke-Johnson meta-GGA functional, are comparable with the available experimental data for the MCN as well as for the band gap. We advise to use modified Becke-Johnson approximation with the parameter c = 1:10 to describe the transition from trivial to topological phase for this class of compounds. [ABSTRACT FROM AUTHOR]

Magnesium based alloys belong to a class of materials, which have recently attracted great interest. In the present work, we report structural, elastic, and thermodynamic properties for the novel intermetallic compound MgNi3 calculated using plane-wave pseudo potential (PW-PP) method within density functional theory (DFT), with local density approximation (LDA) and generalized gradient approximation (GGA). The comparison of the calculated equilibrium lattice constants and experimental data showed very good agreement for both approximations. The elastic constants were determined from a linear fit of the calculated stress-strain function according to Hooke's law. Once the elastic constants were obtained, the bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio - anisotropy factor A, and the ratio B=G for MgNi3 compound were deduced using Voigt-Reuss-Hill (VRH) approximation. Our calculated elastic constants indicate that the ground state structure of MgNi3 is mechanically stable. The calculation results also show that this intermetallic crystal is stiff, elastically anisotropic, and ductile material. The Debye temperature is also predicted from elastic constants. The temperature dependence of the enthalpy H, free energy F, entropy S, and heat capacity at constant volume Cv of MgNi3 crystal in a quasi-harmonic approximation are obtained from phonon density of states and discussed for the first report. [ABSTRACT FROM AUTHOR]

The molecular geometry and vibrational frequencies of (7-chloro-2-oxo-2H-chromen-4-yl)-methyl diethylcarbamodithioate in the ground state have been calculated by using the Hartree-Fock and density functional theory methods (B3LYP and B3PW91) with 6-311++G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray data. The calculated vibrational frequencies are used to determine the types of molecular motions associated with each of the experimental bands observed. To investigate the nonlinear optics properties of the title compound, the polarizability and the first hyperpolarizability are calculated using the density functional B3LYP method. The predicted nonlinear optical properties of the title compound are greater than ones of urea. To determine conformational flexibility, molecular energy profile of the title compound is obtained by B3LYP calculations with respect to selected degree of torsional freedom, which is varied from -180° to +180° in steps of 10°. Besides, molecular electrostatic potential, natural bond orbitals, natural atomic charges, frontier molecular orbitals, and several thermodynamic properties are performed by the density functional theory methods. [ABSTRACT FROM AUTHOR]

In this work, we have used the first-principle calculations approach based on spin-polarized density functional theory, and predicted the half-metallic behavior of In1-xMnxSb alloys (x = 0:25, 0.50, 0.75). The structural, electronic and magnetic properties of these ternary cubic crystals have been investigated. The electronic exchangecorrelation energy has been characterized by the generalized gradient approximation with the WC functional improved by the Tran-Blaha modified Becke-Johnson exchange potential approximation. The calculated formation energy indicates that In1-xMnxSb compounds (at all compositions) are thermodynamically stable, and can be synthesized. Our calculated structural parameters are in good accordance with the available theoretical and experimental data. The ternary alloys In1-xMnxSb are half-metallic ferromagnets with a spin polarization at the Fermi level of 100%. Our investigation shows an antiferromagnetic interaction between Mn-Sb and Mn-In, the total magnetic moment is equal to 4:00 μB for all studied structures. These materials are half-metallic ferromagnets, and thus may be potential candidates for spintronics applications. [ABSTRACT FROM AUTHOR]

The ab initio calculations based on density functional theory were performed to study structural, elastic, and opto-electronic properties of the Cu2MgSiS4 compound in three zinc-blende derived and one wurtzite derived structures. These calculations are carried out using the full potential linear augmented plane wave plus local orbital method, implemented into the WIEN2k computer code. Within generalized gradient approximation based on the revised Perdew-Burke-Ernzerhof exchange-correlation density functional the optimized lattice parameters and atomic positions are found to be in a good agreement with available experimental values. The total energies, obtained at equilibrium of this compound in four phases, reveal that both stannite and wurtzite-stannite are the most energetically favorable structures whereas the kesterite structure remains energetically probable under ambient conditions. The mechanical stability of this compound in these three phases is examined and established. Moreover, several isotropic elastic moduli were estimated via the calculated single crystalline elastic constants. In particular, our results show that this compound in these structures could be classified as ductile material and the highest elastic anisotropy were demonstrated by WS structure. On the other hand, the calculations of the electronic structure and optical properties were performed at the Perdew-Burke-Ernzerhof exchange-correlation density approximation level, improved by the Tran-Blaha modified Becke-Johnson potential to give an enhanced depiction of the band-gap energies and optical spectra. The fundamental band gap for the WS phase is calculated to be 2.44 eV. Analysis of the electronic structure reveals that the Cu(3d)-S(3p) hybridized antibonding state forms the valence band edge, while the conduction band edge is composed of the Si(3s)-S(3p) hybridized antibonding state. The optical response of the material in the visible and ultraviolet range is determined by calculating its complex dielectric tensor. It was observed that this compound in these three phases does not exhibit a large optical anisotropy. The estimated optical band gap 3.10 eV for WS phase is found to be in much closer agreement with the experimental findings. Over all, the obtained results seem to be more reliable compared to previous reported calculations and with available experimental results. [ABSTRACT FROM AUTHOR]

The density functional theory calculations are performed on the structural and electronic properties of the MoS2/BN van der Waals heterostructure under an external electric field (E-field). Our results reveal that the MoS2/BN van der Waals heterostructure has a direct band gap of 1.81 eV in the raw, and electrons prefer to transfer from MoS2 to BN due to the deeper potential of BN monolayer. Moreover, by applying an E-field, ranging from -0.40 to +0.50 V/Å, the band gap decreases from 1.81 eV to zero, which is linked to the direction and strength of the E-field. Through partial density of states plots, it is revealed that d and p orbitals of Mo, S, B, and N atoms are responsible for the significant variations of the band gap. These obtained results predict that the tunable band gap of the MoS2/BN van der Waals heterostructure carries potential applications for nanoelectronic and spintronic devices. [ABSTRACT FROM AUTHOR]

Graphene is an attractive candidate for the future generation of nanoelectronic and nanophotonic devices, gas sensors, biosensors, and batteries for energy storage. The fact that pristine graphene is not magnetic limits its application in areas such as magnetic storage and spintronics. However, recent theoretical and experimental results indicate that adsorption of metal adatoms and substitutional doping are promising ways to modulate the electronic properties and induce a magnetic state of graphene-based systems. Using the density functional theory we study the properties of graphene sheets substitutionally doped with Sc, Ti, and Zn atoms. In particular, the influence of metal doping on geometric structure, electronic structure, and magnetic behavior of graphene were analysed. The obtained results indicate that the optimized geometries show distortion on doping and the electronic structures are significantly modified. To examine the magnetic state of doped graphene both ferromagnetic and antiferromagnetic cases were taken into consideration. [ABSTRACT FROM AUTHOR]

By using density functional theory within the Perdew-Burke-Ernzerhof generalized gradient approximation implemented in the VASP code, we study the structural, elastic, electronic, and thermodynamic properties of C15 Laves-phase compound HfZn2. Comparing the lattice constants calculated from the Perdew-Burke-Ernzerhof generalized gradient approximation and local density approximation, we find that the former is in better agreement with the experimental data. The elastic constants of HfZn2 calculated by strain-stress method indicate that they keep stable up to 100 GPa. The bonding characteristics are discussed by analyzing the energy band structure, charge density distribution and charge density difference. Phonon dispersion curves and phonon density of states of HfZn2 at the different pressure are predicted for the first time. In addition, there is no imaginary frequency in the phonon band at different pressure, which also shows that HfZn2 is stable up to 100 GPa. Vibrational models are also illustrated based on phonon and group theory. The thermodynamic properties under high temperature and high pressure are calculated by different thermodynamic models. The heat capacity at constant pressure and low temperature calculated by quasi-harmonic approximation is more close to the measurement than that calculated by quasi-harmonic Debye models. [ABSTRACT FROM AUTHOR]

A series of InxTl1-xI (x = 0:4-0:9) single crystalline solid state alloys were successfully synthesized by the vertical Bridgman method. For the first time the density functional theory based band structure calculations are performed and features of the band energy dispersion are discussed. Comparison with the experimental energy gap Eg obtained from the optical photoconductivity is discussed. An essential role of the localized defects and excitons in formation of the edge photoconductivity is analyzed. Relation between the crystal structure and photoconductivity of the materials studied is discussed. Also the origin of the principal valence and conduction bands is explored. Experimental measurements of the band gap Eg by the optical and photoconductivity methods have given opposite dependences with respect to the indium content x. Features of the photoconductivity spectra for different crystallographic directions have been discussed with taking into account the chemical bonds anisotropy. [ABSTRACT FROM AUTHOR]

In this article, density functional theory has been used to investigate the structural and optoelectronic properties of PbZrO3 (PZO) under pressure from 0 to 350 GPa. In order to achieve ground state structural stability, generalized gradient approximations has been utilized. By studying electronic properties, indirect band-gap nature of PZO appears to change at 15 GPa to direct band-gap. Optical analysis include under pressure responses of real and imaginary parts of dielectric function, optical conductivity, optical absorption coefficient, energy loss function, refractive index, reflectivity and extinction coefficient. Most of the results have been found to be consistent with literature. Study reveals that static dielectric constant and band-gap are in accordance with the Penn model which validates our computed results. Moreover, static dielectric constant and static refractive index directly increases with pressure. Material preserves its positive value of refractive index at all pressures and therefore, it is not a negative index metamaterial. Plasma frequency increases directly with pressure that destabilize the under study material. Our results could be very useful for developing novel optoelectronic devices based on PZO suitable to work under extreme conditions. [ABSTRACT FROM AUTHOR]

The structural, magnetic, electronic, dynamical and thermodynamic properties of PuN have been studied within the frameworks of the density-functional theory, DFT+U and hybrid DFT. The calculations have been performed using the full-potential-linearized augmented plane-wave method. The ferromagnetic and antiferromagnetic configurations are considered in this work. The lattice constants, bulk moduli, densities of states, and thermodynamic data have been computed and compared to available experimental data and other theoretical calculations published in the literature. Total energy results obtained with DFT+U and hybrid DFT indicate that the ground state of PuN is antiferromagnetic, in agreement with experiment. The chemical bonds between Pu and N have a mixture of covalent and ionic components, but the ionic character is stronger than covalent character. The phonon dispersion curves and the optical-mode frequencies are also reported. At last, the effect of spin-orbit coupling on the structural, magnetic, and electronic properties of PuN has been discussed. [ABSTRACT FROM AUTHOR]

Positron implantation profiles in various materials for 22Na isotope source are discussed. The spatial distribution of positrons in materials with densities from 1 to 21 g/cm³ are simulated using GEANT4 code. The results indicate that depth distributions of thermalized positrons in any homogeneous medium can be described by the sum of two exponential functions. Contribution of the short-range exponent is about 11% in the materials. The both absorption coefficients can be well represented as a function of material density and atomic number. Proposed empirical model agrees well with available experimental data. [ABSTRACT FROM AUTHOR]

A computational study of the ozonolysis of phenanthrene has been carried out using DFT methods (B3LYP and M06-2X). The reaction mechanism for the ozonolysis was studied in both gas phase and in solution, using the polarizable continuum solvation model. The structures for all proposed reaction mechanisms were optimized using M06-2X and B3LYP methods with 6-31G(d), 6-31+G(d), and 6-31G(2df,p) basis sets. In solution, all structures were optimized using B3LYP/6-31+G(d,p) and polarizable continuum solvation model. Six different mechanistic pathways were explored for the ozonolysis of phenanthrene that forms aldehyde compounds. The activation energy of the formation of the primary ozonide intermediate in pathway A is 13 kJ mol-1 in the polarizable continuum model with the B3LYP/6-31+G(d,p) method. This reaction is followed by a dissociation into a zwitterionic Criegee intermediate with an activation energy of 76 kJ mol-1 in polarizable continuum model with B3LYP/6-31+G(d,p). Furthermore, the nucleophilic addition reactions of methanol to the Criegee intermediate have been studied along two pathways, B1 and B2. The water-mediated mechanism for pathways B2 and C2, where the water molecule acts as a mediator through a 1,5-proton shift, dropped the activation barriers by 18 and 26 kJ mol-1, respectively, based on B3LYP/6-31G(2df,p) method. The solvation model (polarizable continuum) reduces the energy barriers for all pathways except for the reaction of methanol with the Criegee intermediate. This study provides an insight into understanding the mechanism of transformation of this pollutant into non-toxic compounds. [ABSTRACT FROM AUTHOR]

We have employed the density functional theory plane-wave pseudopotential method with local density approximation and generalized gradient approximation to investigate the structural, elastic and mechanical properties of the intermetallic compound NiGa. The calculated equilibrium lattice constant and bulk modulus are in good agreement with the experimental and other calculated values. According to our best knowledge, from the elastic constants, the bulk modulus B, anisotropy factor A, shear modulus G, the Young modulus E and the Poisson ratio σ for NiGa compound are obtained for the first time. By comparison, our results for the elastic constants Cij, bulk modulus B, shear modulus G and the Young modulus E are as good as those of NiAl compound. The dependences of the elastic and mechanical parameters of NiGa compound on pressure were also investigated. It was found that the cubic NiGa compound is mechanically stable under pressure according to the elastic stability criteria up to 13 GPa, and it is not elastically isotropic. By analyzing the ratio (B/G), it was concluded that NiGa compound is ductile in nature. [ABSTRACT FROM AUTHOR]

The structure and spectroscopic data of the molecules in the ground state were calculated using density functional theory employing B3LYP/6-311 + +G(d,p) basis set. The dipol moment, linear polarizability and first hyperpolarizability values were also computed using the same basis set. A study on the electronic properties, such as HOMO-LUMO energies, were performed by time-dependent density functional theory approach. A detailed description of spectroscopic behaviour of compounds was given based on the comparison of experimental data and theoretical computations. [ABSTRACT FROM AUTHOR]

Ab initio calculations based on the density functional theory have been performed to investigate the migrations of interstitial helium (He) atoms in Au-Ag alloys with two different mass ratios (Au3Ag2 and AuAg). The results show that the migration mechanisms of He atoms mainly depend on the crystal structures of alloys, and their migration energy barriers are affected by the migration paths in Au-Ag alloys. He interstitials preferentially occupied the most stable sites, but it is difficult for He interstitials to migrate to nearest most stable sites via second stable positions at room temperature. When He atom is at the tetrahedral position which has higher formation energy, it possibly migrates to nearest tetrahedral positions directly for AuAg alloy. In addition, comparing the migration of He defects in the two alloys, we found that the properties of migration energy and relative stability of He atoms probably slightly depend on the mass-density of Au-Ag alloys. [ABSTRACT FROM AUTHOR]

The structural, elastic anisotropy and thermodynamic properties of the P4m2-BC7 are investigated using firstprinciples density functional calculations and the quasi-harmonic Debye model. The obtained structural parameters and elastic modulus are in consistency with the available theoretical data. Elastic constants calculations show that P4m2-BC7 is elastic anisotropic. The bulk modulus as well as other thermodynamic quantities of P4m2-BC7 (including the Grüneisen constant, heat capacity and thermal expansion) on temperatures and pressures have also been obtained. [ABSTRACT FROM AUTHOR]

First principles calculations on structural, elastic and thermodynamic properties of K2S have been made using the full-potential augmented plane-waves plus local orbitals within density functional theory using generalized gradient approximation for exchange correlation potentials. The ground state lattice parameter, bulk moduli have been obtained. The second-order elastic constants, Young and shear modulus, Poisson ratio, have also been calculated. Calculated structural, elastic and other parameters are in good agreement with available data. The elastic constants and thermodynamic quantities under high pressure and temperature are also calculated and discussed. [ABSTRACT FROM AUTHOR]

We investigate the morphology and charge distribution at the (001)-diamond/BN heteropolar junctions of the cubic materials. Our investigations are based on the first principles calculations in the framework of the density functional theory. These studies reveal that reconstruction of the interface leads to possible charge compensation at the interface and increases also the stability of the junction in comparison to the abrupt interfaces. [ABSTRACT FROM AUTHOR]

The electronic structure of Ce1-xLaxPtIn is studied by means of ab initio full-potential local orbital basis (coherent potential approximation) (FPLO-CPA) and spin polarized relativistic Korringa-Kohn-Rostoker (SPRKKR- CPA) methods within the densities functional methodologies. In both methods, we have observed decrease of the density of states at the Fermi level versus of La concentration. The theoretical photoemission spectra of LaPtIn and CePtIn are compared with the experimental data and the agreement is good. We have also reported the optical properties of LaPtIn and CePtIn compounds obtained in GGA and GGA+U approximation. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of alkaline-earth oxide BaO under epitaxial strains are investigated using a first principles density functional theory. The electronic structure is particularly sensitive to the compressive or tensile strain, e.g., the splitting of energy band, the increase of the total density of state, and the shift of the partial density of states. Especially, the trends in the variation of the optical band gap are predicted by two different exchange-correlation potential schemes. Our results indicate that the optical band gaps undergo a decrease for both compressive and tensile strains. [ABSTRACT FROM AUTHOR]

The EPR parameters (g factors g∥, g⊥ and hyperfine structure constants A∥, A⊥) of the tetragonal Ti3+-O2--VM centers in MgO and CaO crystals are calculated from the high-order perturbation formulae based on the cluster approach. The calculated results are in reasonable agreement with the observed values. The local structural parameters for the tetragonal Ti3+ centers in both crystals are also obtained from the calculation. These results are discussed. [ABSTRACT FROM AUTHOR]

The band structure investigations for Sm(Ni1-xCox)3 alloys by means of X-ray photoelectron spectroscopy (XPS) and an ab initio density functional theory (DFT) calculations are presented. The aim was to determine an effect of Ni/Co substitution on the electronic structure of the alloys. Investigations have shown that the Ni/Co substitution results in a reconstruction of the valence band (VB), especially the intensity near the Fermi level decreases with Co content. An ab initio simulated XPS VB spectra agree qualitatively with experimental ones with the exception of the Sm-4f sub-spectra where the multiplet decomposition is observed. Calculations shown that variation of magnetization in Sm(Ni1-xCoxq)3 is driven mainly by the Ni/Co-3d and Sm-5d states polarization and increases linearly with rising Co content. [ABSTRACT FROM AUTHOR]

The DFT estimates of magnetic couplings in molecular nanomagnets are computationally demanding and their values have not achieved the satisfactory accuracy in spite of a lot of effort. We concentrate here on comprehensive tests for predictions of the recently proposed augmented symmetry approach aiming at reducing the computational complexity of the DFT calculations which is particularly important for the Wien2k code. Using the B3LYP functional, we demonstrate the numerical stability of magnetic couplings, magnetic moments and the HOMOLUMO gaps, changing the fraction of exact exchange α. We reach the significant gain in the computing time without a loss in the accuracy of the final results with respect to those obtained by the standard PBE approach. We conclude that the value α = 0:25 leads to best estimation of magnetic couplings for hybrid functionals within Wien2k. [ABSTRACT FROM AUTHOR]

We perform exact numeric calculations for a few versions of the two-orbital Hubbard model on the four site cluster. We show that the conventional spin 1 Heisenberg Hamiltonian can be obtained in the strong coupling limit, but only for some versions of the two-orbital Hubbard model. Then we propose a modified version of the Heisenberg Hamiltonian, that we call the two-orbital Heisenberg model, which is relevant in those cases, where the conventional spin 1 Heisenberg model fails. [ABSTRACT FROM AUTHOR]

We measured thermopower, thermal conductivity and electrical resitivity for Ca2Sn sample across 4-350 K temperature range. Contrary to expectations from recent DFT based calculations the thermopower is not particularly large, reaching 7 μV at 350 K. The thermoelectric figure of merit renders this material in unmodified form practically unusable for thermoelectric aplications. [ABSTRACT FROM AUTHOR]

We study the magnetic behavior of the diamond system. In this system diamond bulk is involved which is doped with different transition metals, namely Cu, Cd, Hg, and Zn. The VASP code is employed for all calculations which are based on density functional theory. The substitutional point defects is introduced in the diamond bulk and occupied by the transition metals. Results exhibit that all transition metals show ferromagnetism behavior and Cu is a good advocate of conductivity among all transition metals. The range of magnetic moments is 2.89, 1.99, 1.96, and 1.80 μB per Cu, Cd, Hg, and Zn atom in diamond bulk, respectively. Strong magnetic behavior points out that these materials could be used for spintronics. [ABSTRACT FROM AUTHOR]

We examine the electronic and magnetic properties of three frustrated Cr9 molecules with a single bond defect using density functional theory method. Five non-equivalent broken-symmetry spin configurations with S = ±3=2 for Cr are considered, the corresponding differences between the total energies are calculated and the exchange interaction parameters J extracted using different scenarios. We find that the couplings for all molecules are antiferrimagnetic. We also estimate the fundamental gaps and in addition, the high occupied molecular orbitals and low occupied molecular orbitals are plotted and discussed. [ABSTRACT FROM AUTHOR]