First principles study of structural and electronic properties of BNNTs

In this article the electronic and structural properties of single-walled boron nitride (BN) nanotubes with a diameter range of 4–22 Å have been investigated using the generalized gradient approximation with both Perdew, Burke and Ernzerhof (PBE) and Becke–Lee–Yang–Parr (BLYP) functionals based on density functional theory. The variation of radial distribution, bond length, lattice constant, density of states, buckling separation, total energies and the electronic band gap of BN nanotubes have been studied in terms of the diameter of the nanotube. Our results revealed a correlation between the buckling and band gap: the higher the buckling, the lower the band gap, and by decreasing the tube diameter, the buckling separation increases. It is revealed that for both armchair and zigzag boron nitride nanotubes (BNNT) the value of the band gap increases by increasing the nanotube diameter. Moreover, it is concluded that for small BN nanotubes by reducing the radius, the band gap of the armchair nanotube remains almost constant, while the band gap of the zigzag nanotubes has a rapidly decreasing trend. The value of band gap obtained by the BLYP hybrid functional is more accurate than the PBE functional. The PDOS calculations revealed that the VBM comes from the N 2p orbitals, while the CBM is ruled by the B 2p orbitals. According to the obtained results, BNNTs are suggested as good materials for applications in the nanoscale optoelectronic devices.     

DFT study on structural,electronic, and optical properties of cubic and monoclinic CuO

First-principles calculations were made to explore the structural, electronic, and optical properties of copper oxide (CuO) with monoclinic (m-CuO) and cubic (c-CuO) structures. We calculated the equilibrium structural parameters: lattice parameters (a, b, and c), angle \(\beta \), and volume V. The obtained results were in good agreement with the experimental data reported in the literature. The cohesive energy showed that m-CuO is more stable than c-CuO. The band structure indicated that c-CuO is an indirect band gap semiconductor with a band gap of 0.87 eV along R–G, while m-CuO has a metallic behavior. Furthermore, electrovalent and covalent bonds were observed in both c-CuO and m-CuO. The linear optical properties were calculated and analyzed along different polarization directions of the incident light. The results indicated that m-CuO possesses optical anisotropic properties. In particular, c-CuO can be used as a potential UV detector material because of its high absorption coefficient (356351.3).     

First-principles investigation of Sn doping on the geometric and electronic structures of V2O5

Abstract

The influence of Sn doping on the geometric and electronic structures of V₂O₅ were investigated by the plane-wave pseudopotential technique based on density functional theory (DFT) with LDA/CA-PZ functional. After Sn doping, the unit cell volume of V₂O₅ increases slightly and the system changes from intrinsic semiconductor to n-type semiconductor. In the Sn doped V₂O₅, the V-O bonds show a significant covalent bond character, while the Sn-O bonds exhibits mainly ionic bond character; the V?=?O bonds from the vanadium and terminal oxygen have the strongest bond strength among all the V-O bonds in the system; in addition, the bond strength of the terminal/apical V-O bonds adjacent to Sn atom weakens obviously.     

Exploring the electronic and optical absorption properties for homo- and hetero-pyrrole-graphene quantum dots

Journal of Computational Electronics - Density functional theory as well as molecular mechanics force field (MMFF94) techniques are used to study intermolecular/intramolecular interactions, band...     

单相电子式电能表的特点及其原理

介绍了单相电子式电能表的特点、结构和工作原理、电能计量芯片特点。     

First principles modeling of disorder scattering in graphene

It is important to investigate impurity scattering phenomena when modeling graphene nanoscale devices, as impurities are invariably present in any realistic system and can significantly influence graphene carrier transport. We present a short review of quantum transport where density functional theory (DFT) is carried out within the nonequilibrium Green’s function formalism (NEGF), focusing on a recent extension of this framework in the form of nonequilibrium vertex correction (NVC) that captures random graphene impurity scattering in a systematic fashion. Our results show that disorder effects significantly alters the electronic and transport properties of graphene devices. We argue that disorder effects should not be ignored if one were to model graphene nanoscale devices in realistic situations, including arriving at fundamental electronic properties such as Ohm’s law.     

A first principles study of key electronic,optical, second and third order nonlinear optical properties of 3-(4-chlorophenyl)-1-(pyridin-3-yl) prop-2-en-1-one: a novel D-$$\pi $$-A type chalcone derivative

In this work we assess the significant electrooptic properties of a novel chalcone derivative 3-(4-chlorophenyl)-1-(pyridin-3-yl) prop-2-en-1-one using a computational approach. The ground-state molecular geometry was optimized, and geometrical parameters and vibrational modes are established and found to be in strong correlation with experimental results. The excitation energy is observed to be 326 nm (3.8 eV), calculated at the TD/B3LYP/6-31G level (stands for time dependent/Becke’s three Lee-Yang-Parr/basis set). Additionally, a unique insight was gained on a number of properties of the molecular levels such as the HOMO-LUMO gap (i.e. \({\sim } 4\,\hbox {eV}\)) and electrostatic potential maps. The potential applications of the 3-(4-chlorophenyl)-1-(pyridin-3-yl)prop-2-en-1-one (CPP) molecule in nonlinear optics are confirmed by second and third harmonic generation studies at five different characteristic wavelengths. The static and dynamic polarizability are found to be many-fold higher than that of urea. The second and third harmonic generation values of the titled molecule are found to be 56 and 158 times higher than standard urea molecule, respectively, computed at same wavelength (i.e. 1064.13 nm). From these studies it is clear that the material possesses superior properties and could be applied in optoelectronic device fabrications.     

Comparison between optical fiber birefringence induced by stressanisotropy and geometric deformation

A variational formulation-based vector perturbation model is used to compare the contribution of stress anisotropy and geometric deformation toward optical fiber birefringence. We show that relative impact of stress on birefringence and differential group delay depends significantly on the exact fiber index profile     

Thermoelectric,electronic and structural properties of CuNMn3 cubic antiperovskite

Using first-principles calculations, in this work we report the structural, electronic and, for the first time, thermoelectric properties of CuNMn3 cubic antiperovskite. The structural properties are explored using GGA and \(\hbox {GGA}{+}\hbox {U}\) approximations. Structural optimization shows that the compound is stable in the ferrimagnetic phase, and the electronic properties confirm the metallicity of this compound. At room temperature, high values of the Seebeck coefficient are obtained between \(-\) 0.8 and 0.5 \(\upmu (\hbox {eV})\) chemical potential, whereas outside this region the Seebeck coefficient diminishes. Also, thermal conductivities are minimal in this region of chemical potential; therefore, the material can be used to achieve thermocouples. Thermal conductivity is high for 900 K. The maximum electrical conductivity is obtained at 0.38 \(\upmu (\hbox {eV})\) chemical potential, with a value of \(4.15\times 10^{20}(\Omega ~\hbox {ms})^{-1}\). The figure of merit ZT values obtained are still low, so for thermoelectric applications of the material, it is necessary to improve the figure of merit coefficient by doping the material with a suitable element.     

Electrical and non-linear optical properties of Ba2NaNb5O15 thin films

Abstract

Tungsten Bronze-type Ba₂NaNb₅O₁₅ (BNN) films were deposited on the fused quartz, Si and substrates using a RF magnetron sputtering method. The sputtering conditions, such as a deposition ratio and rate of the BNN film, were optimized.     

The pressure effects on electronic,thermoelectric, thermodynamic,and optical features of Li3Bi

First-principles electronic, thermoelectric, thermodynamic, and optical calculations of an alkali pnictide compound, Li₃Bi, are implemented by WIEN2k, BoltzTraP and Gibbs2 using density functional theory in the presence of spin–orbit coupling. The generalized gradient approximation and modified Becke and Janson functionals with the generalized gradient approximation are utilized for the treatment of exchange and correlation potential. The Li₃Bi electronic band structure indicates that this compound is a semiconductor at zero pressure. The energy band gap of this compound closes at a pressure of 6.0 GPa. In contrast, low pressures enhance the energy band gap and reduce the band width of the valence and conduction bands. The pressure and temperature effects on the thermoelectric and thermodynamic performance of this compound are investigated. This results reveal (1) an increase in the power factor values under high temperatures and low pressures, (2) a reduction in the thermal expansion and the specific heat capacity at constant volume and an increase in the Debye temperature under high pressures at constant temperature. Also, the evaluation of optical properties under various hydrostatic pressures shows an increase in the static real part of the dielectric function and the static reflectivity of Li₃Bi at a pressure of 6 GPa.

     

Systematic study of elastic,electronic, and magnetic properties of lanthanum cobaltite oxide

The electronic structure, elastic constants, and magnetic properties of lanthanum cobaltite oxide \(\hbox {La}_{4}\hbox {Co}_{3}\hbox {O}_{9}\) compound, which crystallizes in orthorhombic space group Pnma, are investigated theoretically for the first time using the full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory plus Hubbard correction term (DFT \(+\) U). The calculated equilibrium lattice constants and fractional atomic coordinates are in a good agreement with available experimental data. Our result for the formation energy and elastic constants confirms that the predicted \(\hbox {La}_{4}\hbox {Co}_{3}\hbox {O}_{9}\) is mechanically stable. This compound is found to be ductile in nature in accordance with Pugh’s criteria. The anisotropy factors (\({A}_{1})\), (\({A}_{2})\), and (\({A}_{3})\) of \(\hbox {La}_{4}\hbox {Co}_{3}\hbox {O}_{9}\) material are also predicted through the elastic constants. The electronic band structures show metallic behavior; the conductivity is mostly governed by Co-3d and O-2p states. The total magnetic moments of the tetrahedral (\(\hbox {CoO}_{4})\) and octahedral (\(\hbox {CoO}_{6})\) environments are, respectively, 2.502 \(\mu _{B}\) and 2.874 \(\mu _{B}\), which are consistent with the experimental measurements.     

Theoretical investigation of electronic performance,half-metallicity,and magnetic properties of Cr-substituted BaTe

We have investigated the structural, electronic, and ferromagnetic properties of chromium (Cr)-doped rocksalt BaTe (\(\hbox {Ba}_{1-x}\hbox {Cr}_{x}\hbox {Te}\)) compounds with compositions \(x = 0.25\), 0.5, and 0.75, based on density functional theory with generalized gradient approximation of Wu–Cohen (GGA-WC) and Tran–Blaha-modified Becke–Johnson (TB-mBJ) potential using the WIEN2k package. We found that the electronic structure showed half-metallic ferromagnetic character with spin polarization of 100 % around the Fermi level. In addition, the minority-spin bands depicted a half-metallic ferromagnetic (HMF) gap and half-metallic (HM) gap. The improved HMF and HM gaps found with the TB-mBJ potential are higher than with the GGA-WC approximation. These large HM gaps make \(\hbox {Ba}_{1-x} \hbox {Cr}_{x}\hbox {Te}\) compounds promising candidates for use in spintronics applications.     

Simulation of power electronic circuits with principles used inwave digital filters

Simulation is a well-known technique to study complex systems. This paper introduces a new simulation technique based on the theory of wave digital filters. They are candidates to substitute classical analog filters by digital electronic circuits in signal processing. In addition, they show advantages compared with other classes of digital filters such as fast algorithms and simple models of electric components. Therefore, the theory of wave digital filters is used to build a new simulator for transient simulation. So far, the properties of this simulator permit a fair comparison between the new simulation technique and well-known simulation programs. The new simulator is easily linked to a CAD program to design and optimize switch mode power supplies already in use in industry     

Atomistic calculations of the electronic, thermal, and thermoelectric properties of ultra-thin Si layers

Low-dimensional semiconductors are considered promising candidates for thermoelectric applications with enhanced performance because of a drastic reduction in their thermal conductivity, κ _l , and possibilities of enhanced power factors. This is also the case for traditionally poor thermoelectric materials such as silicon. This work presents atomistic simulations for the electronic, thermal, and thermoelectric properties of ultra-thin Si layers of thicknesses below 10 nm. The Linearized Boltzmann theory is coupled: (i) to the atomistic sp³d⁵s^? tight-binding (TB) model for the electronic properties of the thin layers, and (ii) to the modified valence-force-field method (MVFF) for the calculation of the thermal conductivity of the thin layers. We calculate the room temperature electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, and ZT figure of merit of ultra-thin p-type Si layers (UTLs). We describe the numerical formulation of coupling TB and MVFF to the linearized Boltzmann transport formalism. The properties of UTLs are highly anisotropic, and optimized thermoelectric properties can be achieved by the choice of the appropriate transport and confinement orientations, as well as layer thickness.     

Simulating electronic and optical processes in multilayer organic light-emitting devices

A detailed investigation of the device operation of a blue-emitting multilayer organic light-emitting device (OLED) using an electronic device model is presented. In particular, a transient electroluminescence overshoot at turn-on is found to originate from charge and recombination confinement effects at internal interfaces. The location of the emission zone is obtained from the electronic model and its experimental determination exemplified by a sensing layer method. Moreover, the optimization of emission intensity and color is discussed for a red-emitting OLED. The thin-film interference effects are analyzed with help of an optical device model.     

Influence of hydrogen and cerium dopant on structural,optical, and magnetic properties of anatase nanoparticles

Journal of Electroceramics - Cerium-incorporated TiO2 nano-composite powders were fabricated by a facile procedure included co-decomposition of the required chemical complexes. The structures of...     

Sensor and optical properties of ferroelectric and porous fluoropolymers

The fabrication and performance of sensors utilizing the piezoelectric properties of P(VDF/TrFE) copolymer thin films are described. The IR spectra of porous PTFE films, and electron micrographs showing their structure, are presented. Finally the fabrication and performance of a sensor utilizing the piezoelectric properties of a porous PTFE film in contact with a compact or normal PTFE film are described.     

Synthesis and investigations of structural,magnetic and dielectric properties of Cr-substituted W-type Hexaferrites for high frequency applications

Journal of Electroceramics - In current study, Cr-substituted W-type hexaferrites with chemical formula (BaNi2CrxFe16-xO27 for x?=?0.0, 0.1, 0.2, 0.3 and 0.4) have been investigated in...