Search

The hydroxylated carbon nanotubes (CNTs-OH), due to their propensity to trap electrons, are considered in many applications. Despite many case studies, the effect of the electronic structure of the CNT-OH electrode on its oxidation properties has not received in-depth analysis. In the present study, we used Fe(CN)63−/4− and Ru(NH3)63+/2+ as redox probes, which differ in charge. The CNT-OH and CNT electrodes used in the cyclic voltammetry were in the form of freestanding films. The concentration of holes in the CNTs-OH, estimated from the upshift of the Raman G-feature, was 2.9 × 10 13   c m − 2 . The standard rate constant of the heterogeneous electron transfer (HET) between Fe(CN)63−/4− and the CNTs-OH electrode was 25.9 × 10 − 4   c m · s − 1 . The value was more than four times higher than the HET rate on the CNT electrode ( k s = 6.3 × 10 − 4   c m · s − 1 ), which proves excellent boosting of the redox reaction by the holes. The opposite effect was observed for the Ru(NH3)63+/2+ redox couple. While the redox reaction rate constant at the CNT electrode was 1.4 × 10 − 4   c m · s − 1 , there was a significant suppression of the redox reaction at the CNT-OH electrode ( k s < 0.1 × 10 − 4   c m · s − 1 ). Based on the DFT calculations and the Gerischer model, we find that the boosting of the HET from the reduced form of the redox couple to CNT-OH occurs when the reduced forms of the redox couples are negatively charged and the occupied reduced states are aligned with acceptor states of the nanotube electrode. [ABSTRACT FROM AUTHOR]

The local environment of atoms in a semiconductor compound TlInTe2 with tetragonal syngony is studied by the density functional theory (DFT). The introduction of a point defect (indium vacancies) into the TlInTe2 lattice is modeled using supercells. The DFT electronic properties (total and local partial densities of states (PDOS) of electrons) are modeled for the primitive TlInTe2 cell (16 atoms per unit cell) and for the defective TlInTe2 cell (where is the vacancy In) consisting of 32 atoms. The DFT-GGA calculations of the TlInTe2 band structure show that the band gap () is = 1.21 eV. This value is significantly different from the experimental value. The Hubbard model is used to correct the interaction of particles in the lattice. The DFT-GGA + U (U is the Hubbard potential) calculated by the TlInTe2 band gap is 0.97 eV. For the TlInTe2 supercell, the energies of the formation of a vacancy, the chemical potential of indium, and the standard enthalpy of the formation of TlInTe2 are calculated. When explaining the effect of various factors on the transport phenomena in TlInTe2, their thermal and electrical conductivity, both the DFT-calculated data and experimental data, are used. Taking into account the experimental data for the p‑TlInTe2 crystals, the mechanism of conduction in the direction of structural chains (c axis of the crystal) is established. From the experimental data in the temperature range = 148–430 K, the band gap = 0.94 eV and the activation energy of impurity conduction = 0.1 eV (at 210–300 K) are estimated. At temperatures of ≤ 210 K, DC hopping conduction takes place in the p-TlInTe2 crystals. With this in mind, the following physical parameters are calculated for p-TlInTe2: the density of states localized near the Fermi level, their energy spread, and the average hopping distance. [ABSTRACT FROM AUTHOR]

The local environment of atoms in a semiconductor compound TlInTe2 with tetragonal syngony is studied by the density functional theory (DFT). The introduction of a point defect (indium vacancies) into the TlInTe2 lattice is modeled using supercells. The DFT electronic properties (total and local partial densities of states (PDOS) of electrons) are modeled for the primitive TlInTe2 cell (16 atoms per unit cell) and for the defective TlInTe2 cell (where is the vacancy In) consisting of 32 atoms. The DFT-GGA calculations of the TlInTe2 band structure show that the band gap () is = 1.21 eV. This value is significantly different from the experimental value. The Hubbard model is used to correct the interaction of particles in the lattice. The DFT-GGA + U (U is the Hubbard potential) calculated by the TlInTe2 band gap is 0.97 eV. For the TlInTe2 supercell, the energies of the formation of a vacancy, the chemical potential of indium, and the standard enthalpy of the formation of TlInTe2 are calculated. When explaining the effect of various factors on the transport phenomena in TlInTe2, their thermal and electrical conductivity, both the DFT-calculated data and experimental data, are used. Taking into account the experimental data for the p‑TlInTe2 crystals, the mechanism of conduction in the direction of structural chains (c axis of the crystal) is established. From the experimental data in the temperature range = 148–430 K, the band gap = 0.94 eV and the activation energy of impurity conduction = 0.1 eV (at 210–300 K) are estimated. At temperatures of ≤ 210 K, DC hopping conduction takes place in the p-TlInTe2 crystals. With this in mind, the following physical parameters are calculated for p-TlInTe2: the density of states localized near the Fermi level, their energy spread, and the average hopping distance. [ABSTRACT FROM AUTHOR]

While it is known that the double-layer Bi 2 Sr 2 CaCu 2 O 8 + y (BSCCO) cuprate superconductor exhibits a one-dimensional (1D) incommensurate superlattice (IS), the effect of IS on the electronic structure remains elusive. Following the recent shift of interest from an underdoped phase to optimum and overdoped phases in BSCCO by increasing the hole doping x, controlled by the oxygen interstitials concentration y, here we focus on the multiple splitting of the density of states (DOS) peaks and emergence of higher order van Hove singularities (VHS) due to the 1D incommensurate superlattice. It is known that the 1D incommensurate wave vector q = ϵ b (where b is the reciprocal lattice vector of the orthorhombic lattice) is controlled by the misfit strain between different atomic layers in the range 0.209 – 0.215 in BSCCO and in the range 0.209 – 0.25 in Bi 2 Sr 2 Ca 1 − x Y x Cu 2 O 8 + y (BSCYCO). This work reports the theoretical calculation of a complex pattern of VHS due to the 1D incommensurate superlattice with large 1D quasi-commensurate supercells with the wave vector ϵ = 9 / η in the range 36 > η > 43 . The similarity of the complex VHS splitting and appearing of higher order VHS in a mismatched CuO 2 bilayer with VHS due to the moiré lattice in strained twisted bilayer graphene is discussed. This makes a mismatched CuO 2 bilayer quite promising for constructing quantum devices with tuned physical characteristics. [ABSTRACT FROM AUTHOR]

The results of studies by the density functional theory (DFT) method of the density of the electronic states (DOS) of supercells of the interface of defective graphene/Ge are presented. The regularities of the change in DOS in the series graphene/Ge → graphene + vacancy/Ge (GPV) are studied. The features of the distribution of the density of electronic states at the ordered vacancy–graphene/Ge interface are discussed. The nature of the bond between graphene and germanium and the adsorption properties of the GPV–Ge system are studied based on the DFT calculations and physicochemical modeling. [ABSTRACT FROM AUTHOR]

The electronic structure and optical properties of AgIn1−xGaxY2 (Y = Se, Te) are investigated using first-principles calculations based on density functional theory. Both the local density approximation (LDA) and generalized gradient approximation (GGA) are employed in the calculation. The crystal structure of ternary semiconductors is the tetragonal chalcopyrite structure with space group I 4 ¯ 2d . The lattice parameters a(Å) and c(Å) are found to vary with the change in Ga composition. The energy gap across the Fermi level in the density of states plots shows that these materials are semiconductors. To compute accurate energy gap values, the LDA + U method is adopted. The calculated elastic constants indicate that these compounds are mechanically stable at normal pressure. The semiconducting nature of these materials may prove their applications in solar cells and photovoltaic absorbers. The optical parameters such as dielectric function, electron energy loss function, refractive index and reflectivity are computed. [ABSTRACT FROM AUTHOR]

The structural, electronic and thermodynamic properties of LaRuX (X = Si, Ge) compounds are investigated using density functional theory by the Wien2k code. Using the first-principles procedure, the Hubbard parameter of La 5d electrons and Ru 4d electrons of LaRuX (X = Si, Ge) compounds is calculated. In these calculations, the exchange–correlation potential is calculated using the generalized gradient approximation (GGA) and generalized gradient approximation plus Hubbard parameter (GGA + U). The calculated results indicate that LaRuX (X = Si, Ge) compounds are stable in the nonmagnetic phase. The electron density of states and band structure of LaRuX (X = Si, Ge) compounds within GGA and GGA + U approaches in the presence of spin orbit coupling are calculated. The obtained results of the electronic band structure show that LaRuX (X = Si, Ge) compounds have metallic behavior. Furthermore, thermodynamic properties of LaRuX (X = Si, Ge) compounds using the quasi-harmonic Debye model within GGA and GGA + U approaches are investigated. [ABSTRACT FROM AUTHOR]

Monolayer MnCX3 metal–carbon trichalcogenides have been investigated by using the first-principle calculations. The compounds show half-metallic ferromagnetic characters. Our results reveal that their electronic and magnetic properties can be altered by applying uniaxial or biaxial strain. By tuning the strength of the external strain, the electronic bandgap and magnetic ordering of the compounds change and result in a phase transition from the half-metallic to the semiconducting phase. Furthermore, the vibrational and thermodynamic stability of the two-dimensional structure has been verified by calculating the phonon dispersion and molecular dynamics. Our study paves guidance for the potential applications of these two mono-layers in the future for spintronics and straintronics devices. [ABSTRACT FROM AUTHOR]

While it is known that the double-layer Bi2Sr2CaCu2O8+y (BSCCO) cuprate superconductor exhibits a one-dimensional (1D) incommensurate superlattice (IS), the effect of IS on the electronic structure remains elusive. Following the recent shift of interest from an underdoped phase to optimum and overdoped phases in BSCCO by increasing the hole doping x, controlled by the oxygen interstitials concentration y, here we focus on the multiple splitting of the density of states (DOS) peaks and emergence of higher order van Hove singularities (VHS) due to the 1D incommensurate superlattice. It is known that the 1D incommensurate wave vector q=ϵb (where b is the reciprocal lattice vector of the orthorhombic lattice) is controlled by the misfit strain between different atomic layers in the range 0.209–0.215 in BSCCO and in the range 0.209–0.25 in Bi2Sr2Ca1−xYxCu2O8+y (BSCYCO). This work reports the theoretical calculation of a complex pattern of VHS due to the 1D incommensurate superlattice with large 1D quasi-commensurate supercells with the wave vector ϵ=9/η in the range 36>η>43. The similarity of the complex VHS splitting and appearing of higher order VHS in a mismatched CuO2 bilayer with VHS due to the moiré lattice in strained twisted bilayer graphene is discussed. This makes a mismatched CuO2 bilayer quite promising for constructing quantum devices with tuned physical characteristics.

Within the framework of the coherent potential approximation for the s-d model, we compute the electrical resistivity and Hall coefficient of disordered paramagnetic Au Pd alloys, taking the electron–phonon interaction into account. Based on the example of these alloys, the mechanisms responsible for the correlation between the resistivity and its temperature coefficient (Mooij rule) and the correlation between temperature dependencies of and are discussed. The results are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The thermal electromotive force (TEMF) and the thermal electromotive force coefficient (TEMFC) of the thermocouple consisting of a copper wire and an (X5CrNi1810) steel wire plastically deformed under tension or bending conditions were found to increase with increasing degree of plastic deformation. The increase in the degree of deformation disturbs the microstructure of steel due to increases in the density of chaotically distributed dislocations and internal microstress, resulting in a decrease in the electron density of states near the Fermi level. Through the effect of thermal energy, annealing at elevated temperatures up to 300°C leads to microstructural ordering along with simultaneous increases in the free electron density of states, TEMF and TEMFC. Based on the temporal change of the TEMF, the kinetics of microstructural ordering was determined. During the initial time interval, the process is a kinetically controlled first-order reaction. In the second time interval, the process is controlled by the diffusion of reactant species. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172057 and Grant no. TR35037]

Copyright of Nanosistemi, Nanomateriali, Nanotehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Structural, electronic, mechanical, thermodynamic and thermoelectric properties of Alkaline fluroperovskites ACdF3 (A = K, Rb, Cs) have been explored using the FP-LAPW method from the perspective of density functional theory (DFT) as employed in the Wien2k package within the generalized gradient approximation (GGA) as well as the local spin density approximation (LSDA). The volume optimization calculations of these materials agree well with experimental as well as available theoretical values. From the energy dispersion curves as well as DOS plots, all the investigated alkali fluroperovskites are found to have an indirect bandgap in Γ -M direction using both approximations. The second-order elastic constants as well as mechanical properties such as Young's modulus, shear modulus, density, anisotropic factor, B/G H ratio are also computed for these materials. In order to study the thermal and vibrational effects on the studied fluroperovskites, we have employed the quasi-harmonic Debye model that uses a set of energy versus volume calculations. The effects of temperature as well as pressure on the structural parameters are also studied using the non-equilibrium Gibbs function. The transport properties of these perovskites have been investigated using BoltzTrap Code. Comparatively, a good figure of merit of these compounds reveals their possible use in thermoelectric applications. [ABSTRACT FROM AUTHOR]

Our previous study of XFeSi (X = La, Gd, Tb) bulks shows that Fe atom has negligible contribution to the magnetic properties of these compounds. In this paper, the contribution of Fe atom to the magnetic properties of XFeSi (X = La, Gd, Tb) nano-layers is investigated. The calculated results are performed based on the density functional theory. The exchange–correlation potential is calculated using generalized gradient approximation and generalized gradient approximation plus Hubbard parameter. The structural, electronic and magnetic properties of XFeSi (X = La, Gd, Tb) nano-layers are investigated in the presence of spin–orbit coupling. The calculated results are compared with the corresponding results of their bulks. Furthermore, the thermodynamic properties of these nano-layers are investigated using the quasi-harmonic Debye model. The bulk modulus, Debye temperature, specific heat at constant pressure and volume and thermal expansion coefficient of these nano-layers are calculated and compared with the corresponding results of their bulks. [ABSTRACT FROM AUTHOR]

Atomic structure of an Ag-containing 4A zeolite with the Ag/Al atomic ratio of about 10% was investigated by a pair distribution function (pdf) analysis. Valence- and conduction-band O 2 p partial electronic structures of this insulating material were respectively measured by soft X-ray emission and absorption spectroscopies using an O 1 s -2 p resonance technique. Moreover, a density functional theory (DFT) hybridized by 25% of Hartree–Fock exchange was applied to determine the atomic structures and electronic states. Although the box size of the DFT calculation was small due to the limited computational power, the present DFT results excellently reproduce the pdf data as well as O 2 p partial electron density of states (DOS). The electronic charge distributions in this zeolite with an antibacterial function obtained by the present DFT calculation revealed half-filled charges on the Ag atoms, which may act as a formation of deactivating the bacteria. [Display omitted] • Atomic structures of Ag containing zeolite were studied by a pair distribution function analysis. • Electronic structures were obtained by soft X-ray absorption and emission spectroscopies. • DFT calculations were carried out for obtaining basic knowledges beyond the experimental data. • Antibacterial function is related to a smattering charge on the Ag atoms for a free radical effect. [ABSTRACT FROM AUTHOR]

We study theoretically the features of impurity-induced states on the surface of a three-dimensional Weyl semimetal in this work. For calculating the impurity-induced local density of states based on T -matrix formulation, we found that for different Weyl semimetal phases the behaviors of a local impurity exhibit distinguishable prominent features for the surface Fermi arc states. Due to two opposite-directional and -chirality surface currents for a surface, a bound state appears at the unitary limit of scattering intensity near the impurity site. Then the resonance condition for different Weyl semimetal phases and scattering intensity is investigated. Our results can be used to identify distinctive topological phases of Weyl semimetal. Furthermore, the relevance of topological nodal-point and -line systems is discussed. Some relation between our theoretical results and current experimental scheme are also discussed. [ABSTRACT FROM AUTHOR]

Adsorption of water on (001)-terminated α-V 2 O 5 surface has been investigated in the framework of density functional theory. According to our calculations, molecular adsorption is preferred, and two types of adsorption sites (Lewis acid center on V atom and Lewis base center on O atoms) have been found. Water adsorption on Lewis acid site does not change the electronic structure of V 2 O 5 surface. Adsorption on Lewis base site is less favorable but reduces the band gap value by half (from 2.5 to 1.3 eV). The reason of this decreasing is the localization of the non-bonding 1 b 2 electron state of water molecule within the forbidden gap of V 2 O 5 surface. The idealized structure of V 2 O 5 ∙ n H 2 O xerogel has been computationally studied at n  = 0 and 1. It is proved that only Lewis base sites are suitable for water positions. At n  = 1, the water absorption energy in xerogel is close to adsorption energy of water on the oxygen atoms of α-V 2 O 5 surface. The presence of the non-bonding states of physically absorbed water in the forbidden gap is also found in the xerogel case. This results in decreasing of the band gap from 2.7 eV to 0.7 eV. [ABSTRACT FROM AUTHOR]

A theoretical study of NO2 sensing capability of MoS2 doped with elements including Si and Fe is carried out. To understand the interaction effects between MoS2 and NO2 in consideration of electronic transport properties has been observed carefully. By bringing dopants and defects into the 2D sheets of MoS2 have significant effects on transport properties which are observed from I-V curves. Finally, we conclude that MoS2 can be used as potential gas sensor and the sensing properties of MoS2 can be enhanced with Fe dopant. [ABSTRACT FROM AUTHOR]

The temperature dependences of the electrical resistivity and thermal electromotive force (thermal e.m.f.) of the Ni-25 at % V, Ni-28 at % V, and Ni-33 at % V alloys in a temperature range of 300-1600 K have been reported; the dependences have been measured during slow heating and cooling of quenched and annealed samples. It has been shown that, near the order-disorder phase-transformation temperature, the temperature dependences of the electrical resistivity of the NiV and NiV alloys demonstrate a kink (second-order phase transition) and a jump (first-order phase transition), respectively. The behavior of the experimental dependences is discussed in terms of the band Mott s-d scattering model. [ABSTRACT FROM AUTHOR]

The structural, elastic, vibrational, thermodynamic and electronic properties of the Mo 2 B intermetallic under pressure are assessed using first-principles calculations based on the generalized gradient approximation (GGA) proposed by Perdew-Wang (PW91). Our results show that the calculated structural parameters at a pressure of zero GPa are in good agreement with the available experimental data. The effect of high pressures on the lattice constants shows that the compression along the c-axis and along the a-axis are similar. The elastic constants were calculated using the static finite strain technique, and the bulk shear moduli are derived from the ideal polycrystalline aggregate. We find that the elastic constants, elastic modulus and hardness monotonically increase as a function of pressure; consequently, the structure is dynamically stable and tends from brittle to ductile behavior under pressure. The Debye temperature θ D increases and the so-called Gr u ¨ neisen constant γ decreases due to stiffening of the crystal structure. The phonon dispersion curves were obtained using the direct method. Additionally, the internal energy (ΔE), the Helmholtz free energy (ΔF), the entropy (S) and the lattice contribution to the heat capacity C v were calculated and analyzed with the help of the phonon dispersion curves. The N(E F ) and the electron transfer between the B and Mo atoms increase as a function of pressure. [ABSTRACT FROM AUTHOR]

First-principles calculations based on density functional theory have been done on the technologically important liquid crystalline material azobenzene. The orthorhombic structure of azobenzene has been simulated and the structural parameters have been found out. Structures of Ortho-fluorinated and Para-fluorinated azobenzene have also been simulated. Electron density of states (EDOS) have been computed in all the three cases which exhibits a narrow band gap and are looking similar to that of a semiconductor in all the three cases. Dielectric constant of the material has been computed and it has been observed that the value of dielectric constant decreases due to fluorination. Phonon modes computed in all the three cases show that the structure is very much stable in all the three cases. [ABSTRACT FROM AUTHOR]

Mixed-valence manganites gain increasing attentions thanks to their extraordinary properties including half-metallicity and colossal magnetoresistive response, rendering them ideal candidate for oxide spintronics applications. Oxygen vacancies in oxides have been approved to be important functional defects and are effective to manipulating their multifunctional properties. To gain a deep insight into the roles of oxygen vacancies on regulating the atomic structure and electronic properties of the mixed-valence manganites, two high-quality epitaxial La2/3Sr1/3MnO3 films around a critical point (without/with oxygen vacancies) were designed and fabricated. From the experiments and theoretical calculations, it was found that the oxygen vacancies induce a weakening of Mn-O-Mn hybridized bond and an increase of concentration of Mn3+ ions, impair the double exchange between Mn3+ and Mn4+, and therefore lead to the transition from metal to insulator and the degraded magnetic properties. Our finding demonstrates a practical approach to tune the magnetic and transport properties of oxide thin films by precisely controlling the oxygen vacancies for high performance spintronics applications. [ABSTRACT FROM AUTHOR]

First-principles calculations based on density functional theory have been done on the chlorinated phenyl benzamides; 4-chloro-phenyl-benzamide – C13H10ClNO, and 2-chloro-3-chloro-phenyl-benzamide – C13H9Cl2NO. The triclinic structure of 4-chloro-phenyl-benzamide and orthorhombic structure of 2-chloro-3-chloro-phenyl-benzamide have been simulated and the structural parameters have been found out. Electron density of states has been computed in the materials using the electronic structure calculation code of Quantum-Espresso which gives a band gap of 0.74 eV in case of 4-chloro-phenyl-benzamide. This value is close to the value exhibited by semiconducting materials and photonic band gap materials. Band gap in case of 2-chloro-3-chloro-phenyl-benzamide comes out to be 3.08 eV. This value is in the range exhibited by NLO materials. Dielectric constant of the materials has been computed. The value of dielectric constant in 4-chloro-phenyl-benzamide comes out to be 2.78, 3.14, and 3.92 along X, Y, and Z axes, respectively, and the average value comes out to be 3.28. The value of dielectric constant in case of 2-chloro-3-chloro-phenyl-benzamide comes out to be 1.39, 1.53, and 1.34 along X, Y, and Z axes, respectively, and the average value comes out to be 1.42. Thus, additional chlorination is increasing the band gap and decreasing the dielectric constant in phenyl benzamide. [ABSTRACT FROM AUTHOR]

We present low-dimensional functionalization and characterization of electron density of states using highly correlated/precisely guided proton beam trajectories and a silicon nanocrystal as a target, representing at a same time a versatile nanolaser technique capable for coherent control of atomic quantum states and for scanning the interior of an atom with resolution comparable to 10% of the Bohr radius. [ABSTRACT FROM PUBLISHER]

Ab initio quantum modeling is applied to check the ideas that motivated studies of both plasma phase transition (PPT) and Brazhkin semiconductor-to-metal phase transition, and to analyze both similarity and difference between them as well as with the Wigner metallization. Electron density of states and the characteristic gap in it are investigated to verify the semiconductor-to-metal nature of the transition. The change of plasma frequency is suggested to be used instead of the 'degree of ionization' to characterize the difference between two plasma phases at PPT. Electron density of states, pair distribution function, and conductivity are calculated as well. It is shown that Norman-Starostin ideas about (a) PPT and (b) phase diagram for fluids are not anymore a hypothesis. They are confirmed by the experimental data. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The results of calculations by PM3 and LDA-DFT methods of the structure and properties of six new polymorphic types of diamond, in which all atomic sites are crystallographically equivalent, are presented. The structures of LA5 ( Cmca), LA7 ( Cmcm), and LA8 ( I4/ amd) phases are obtained as a result of stitching graphene layers and of CA9 $$(Fd\bar 3m)$$, CA10 $$(R\bar 3m)$$, and CA11 ( P6/ mmc) phases by stitching fullerenelike clusters. For these phases the geometrically optimized structures are calculated and the structural parameters, density, sublimation energy, bulk modulus, electron density of states, and X-ray diffraction pattern are measured. It is found that the properties of polymorphic types of diamond depend on the degree of their structure deformation in comparison with the cubic diamond structure. [ABSTRACT FROM AUTHOR]

Abstract: We investigate whether well-known DFT-GGA errors in predicting the chemisorption energy (E chem) of CO on transition metal surfaces manifest in analogous NO chemisorption systems. While widely investigated in the case of CO/metal, analogous DFT-GGA errors have long been claimed to be absent in NO/metal chemisorption. Here, we provide theoretical evidence of systematic enhanced back-donation in NO/metal chemisorption at the DFT-GGA level. We use electronic structure analysis to show that the partially filled molecular NO 2π ⁎ orbital rehybridizes with the transition metal d-band to form new bonding and anti-bonding states. We relate the back-donation charge transfer associated with chemisorption to the promotion of an electron from the 5σ orbital to the 2π ⁎ orbital in the gas-phase NO G2Σ− ←X2Π excitation. We establish linear relationships between E chem and ΔE G←X and formulate an E chem correction scheme in the style of Mason et al. [Physical Review B 69, 161401(R)]. We apply the NO E chem correction method to the (111) surfaces of Pt, Pd, Rh, and Ir, with NO chemisorption modeled at a coverage of 0.25ML. We note that the slope of E chem vs. ΔE G←X and the dipole moment depend strongly on adsorption site for each metal, and we construct an approximate correction scheme which we test using NO/Pt(100) chemisorption. [Copyright &y& Elsevier]

Spin-polarized calculations of three half-metallic, half-Heusler compounds, namely NiMnSb, PdMnSb and PtMnSb are presented. The calculations were performed using tight-binding linear muffin-tin orbital method within the local density approximation. In this work, the lattice constants, bulk modulus, band structures, density of states and energy gap in the minority spin direction and magnetic moment of these compounds were calculated at ambient conditions and under pressure. The effect of pressure on the magnetic properties and on the energy gap was studied. We have predicted that NiMnSb, PdMnSb and PtMnSb show the magnetic phase transition under pressure from the ferromagnetic to nonmagnetic phase at 195.6, 292.4 and 533 GPa, respectively. The magnetic phase transition is of second order in nature. The transition pressure increases from Ni(3 d) to Pt(5 d) in the compound. The calculated energy gap in the minority spin direction increases with pressure. The bulk modulus of these compounds have been predicted to be 140.2, 137.25 and 157.45 GPa, respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied the band structure and Fermi surface of LaO1−x F x BiS2. [•] Studied the Fermi surface nesting at different electron and hole-doping. [•] We calculated the bare susceptibility and found it is different with LaOFeAs. [Copyright &y& Elsevier]

Abstract: We report measurements of the specific heat of two samples of carbon-doped MgB2, Mg(B1− x C x )2, x =0.05 and 0.1, in magnetic fields to μ 0 H =9 T and at temperatures from ∼1 K to somewhat above the critical temperature for superconductivity for each sample. The carbon doping reduced the critical temperature from 39K for MgB2 to 31.4K and 19.7K for the x =0.05 and 0.1 samples, respectively. The results give the electron–phonon coupling and the electron density of states, including the individual contributions of the π and σ bands. These quantities are compared with theoretical calculations. The results also give the energy gaps on the π and σ bands, which are compared with other experimental determinations, and also with theoretical calculations that include predictions of the “merging” of the two gaps as a consequence of the band filling and increased interband scattering associated with doping. [Copyright &y& Elsevier]

An interaction of an electron with phonon in a crystal shows the dependence of electronic heat capacity on temperature in low temperature limit. It is also found from theory that electronic heat capacity is a linear as well as non-linear function of electron-phonon coupling constant, linear function of force constant change parameter and polaron state upto second order. An electron Green's function has been evaluated using equation of motion technique of quantum dynamics. The response function has been obtained from electron Green's function to give electron-phonon linewidth and shift. This electron-phonon linewidth has been responsible for electron density of states. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of 15 different transition metal adatoms on graphene is studied using first-principles density-functional theory with the generalized gradient approximation. The adsorption energy, stable geometry, density of state, and magnetic moment of each adatom–graphene system are calculated. For the adatoms studied from Sc to Zn of the Periodic Table, and noble metals, the distortion of the graphene layer on B of T sites is quite significant in some cases, and the adsorption is characterized by strong hybridization between adatom and graphene electronic states. The favored adsorption site indicates the main chemical bond between adsorbate and graphene. Half filled d shell TM atoms and Au, Ag, Zn have small adsorption energy. The reduction in magnetic moment from the isolated to the adsorbed atom is explained by the perspective of charge transfer, and electron shift between different orbit states of the adatom. [Copyright &y& Elsevier]

Abstract: One-dimensional atomic chains can be synthesized on stepped surfaces and the electronic structure of the high vicinal surface plays an essential role in determining the physical properties of atomic chains grown on top of it. We have applied surface analysis techniques to study the surface of a Pt(997) single crystal. The STM image of the surface showed that the surface was uniform with a well defined distance between the terraces. Angle resolved photoemission spectroscopy (ARPES) was used to characterize the electronic states of the Pt(997) surface, and confinement of electrons with wave vector perpendicular to the step direction was observed. [Copyright &y& Elsevier]

Abstract: We focused our study on the hydrated polyethylenimine (PEI) crystals which are characterized by the presence of 0.5, 1.5 or 2 water molecules per ethylenimine monomer unit. We propose a theoretical study in the framework of periodic linear combination of atomic orbitals (LCAO) using different Hamiltonians based on density functional theory (DFT) and hybrid Hartree–Fock (HF) – DFT level of theory. Once hydrogen atoms added when missing and redundant atoms withdrawn in the PEI structures, ab initio calculations yielded relaxed geometries at the ground state. The closest structural parameters to the experimental values are observed for hybrid Hamiltonians and the use of the 6-31++G∗ basis set reduces this difference. We provide the IR vibration modes at the Γ point, with assignments of the bands. The electronic study reveals that these PEI hydrates have an insulating character with a quasi constant band gap whatever the number of water molecules. From the projected density of states (PDOS), we have found that the nitrogen orbital has the major contribution to the valence band, while the conduction band is mainly constructed from hydrogen bondings. [Copyright &y& Elsevier]

The lowest total energy crystal structure of Li[sub2]MgN[sub2]H[sub2] was identified by the first principle calculation with RPBE exchange-correlation function. Furthermore, the fine structure parameters of this crystal structure were calculated with PBE and PW91 exchange-correlation function. In a further step, the density of states, electron density, charge density difference on (0 0 1) plane and heat of formation of Li[sub2]MgN[sub2]H[sub2] hydrogenation were computed with PW91 exchange-correlation function. Consequently, the electronic structures and chemical bonds in this compound were analyzed and discussed, and then the thermodynamic character of Li[sub2]MgN[sub2]H[sub2] for hydrogen storage was evacuated. [ABSTRACT FROM AUTHOR]

The influence of Ag, Ni and Ti on the electronic properties of Bi2Te3 has been analysed. The relaxation of clean Bi2Te3(0001) surface and relaxation of silver, nickel and titanium on clean Bi2Te3(0001) surface have been studied using ab-initio density-functional techniques. STM images of surface, the total density of states and the band structure of bismuth telluride were determined by using the Quantum-Espresso ab-initio simulation package based on pseudopotential method. The relaxation was performed on a 8x8x1 k-point mesh, whereas in the calculations of the density of states the 12x12x1 k-point mesh was used. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the structural and electronic properties including band structure, energy gap and density of states have been studied for different phases of Pb(Zr1−x Ti x )O3 compounds with a wide range of Ti/Zr ratio (i.e. from x =0 to x =1). The calculations were performed in the framework of density functional theory (DFT), using the full potential-linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). In general, our results show that for all cases (x =0, 0.33, 0.5, 0.66 and 1) by increasing the amount of Ti atoms the band gap decreases, because of the strong hybridization between Ti-3d and O-2p orbital. But, in other hand, decreasing the crystal symmetry results in widening the band gap. For the monoclinic phase (x =0.5) the effect of excess Ti on the band gap is less than the effect of crystal symmetry, so there is an increase in the band gap. [Copyright &y& Elsevier]

Abstract: The nanostructured powders of the Ni95.4Mo4.6 and Ni99Mo1 alloys (average crystallite dimensions of 14 and 21nm) were obtained by the electrochemical deposition from ammonium solutions of nickel and molybdenum salts. The method of differential scanning calorimetry (DSC) and measurement of temperature dependence of the powder''s electrical resistivity, magnetic permeability and the thermoelectromotive force were employed to examine structural changes of the powders. The nanocrystalline alloys Ni95.4Mo4.6 and Ni99Mo1 were stable up to about 460K. The thermal stabilization of the alloys takes place within the temperature interval of 460–570K. As a result of this process, a decrease in the electrical resistivity and increases in magnetic permeability as well as electron state density in the proximity of the Fermi level are observed. The crystallization temperature depends upon the current density of powder formation. The nanocrystalline alloy Ni95.4Mo4.6 obtained at j=70mAcm−2 becomes crystallized in the temperature range between 650 and 840K, while the Ni99Mo1 alloy obtained at j=180mAcm−2 crystallizes in the 580–950K temperature interval. The electrical resistivity and magnetic permeability of the nanocrystalline alloy decreased while the alloy''s electron state density near the Fermi level increased after the process of crystallization took place. The electrical resistivity decrease recorded during the structural changes was due to an increase in the electron state density in the proximity of the Fermi level, as well as to an increase in the mean free path of the conducting electrons. [Copyright &y& Elsevier]