Calculated Band Width Research Articles

Insight on Cu-doping dependent structural, electronic and optical properties of AgZnF3 Fluro-perovskite for solar cell applications: A DFT study

The density function theory (DFT) with GGA and PBE was employed to determine the structural, electrical, and optical characteristics of pure and Cu doped AgZnF3 type Fluro-perovskite. The structural properties of composite are calculated in realistic agreement with those testified in the literature. The band gap of the hybrid AgZnF3 is small and indirect. AgZnF3 contained a calculated band width of 1.52 eV. AgZnF3's total electronic properties were principally controlled by the Zn atom, whereas the Zn-d state and the F-p state had a minor impact on its partial electronic properties and state density. Cu doping modified AgZnF3's electrical band structure by narrowing the band gap. With increasing doping concentrations, the partial densities of states, which are likewise impacted by doping concentrations decreased. This material is appropriate for a variety of applications due to the improvement in optical characteristics and decrease in the band gap.

Design of Ultra-Wideband Microstrip Antennas with Slots and Fractal Based Ground Plane

A rectangular microstrip antenna with slotted and fractal based ground plane has been introduced in this paper as a candidate for use in ultra-wideband applications. The slotted ground structure of the proposed antenna has been created on the radiating patch in two steps. At first, two slots have been made in the ground plane which offers a maximum impedance bandwidth (3.22 GHz to 10.6 GHz). In the second design, carpet Sierpinski type of the 2nd iteration are made in the ground plane the calculation bandwidth is (3.2 GHz to 12.6). The presented antenna has been fed with a single 50 Ohm strip line. The resulting antenna has a rectangular patch with dimensions of (11 mm x15mm). The characteristics of the proposed antenna structure have been predicated using full–wave numerical Method of Moment (MOM) by Microwave Office v. 7.5.

FPGA-accelerated textured surface defect segmentation based on complete period Fourier reconstruction

Real-time detection of surface defects in high-generation, large-size Liquid Crystal Display (LCD) panels is a serious challenge for both image algorithms and processing speed. For the defect detection of Thin Film Transistor-Liquid Crystal Display (TFT-LCD) images, effectively processing the periodic texture composed of gate lines and data lines is a prerequisite for the success of the algorithm. The traditional one-dimensional Fourier reconstruction algorithm uses a filter-based method to remove most of the texture, but due to the spectral leakage problem, the image boundary cannot be effectively processed. The compensation based on the period extension introduces a more complex ringing effect at the image connection. Starting from the implicit periodic principle of Fourier transform, we propose a strategy of complete period truncation based on subpixel period, which completely eliminates the boundary texture. Furthermore, we fully exploit the potential of parallel execution of the algorithm, resampling the liquid crystal segments truncated in the complete period to an integer power length of 2. The FPGA structure of one-dimensional Fourier reconstruction defect segmentation algorithm with dual-task parallelism and two-pixel parallelism is designed and the calculation bandwidth of 500 MB/s can be realized at 125-MHz clock frequency. We demonstrate the superiority of the proposed method qualitatively and quantitatively. The one-dimensional Fourier reconstruction algorithm based on the complete period truncation can effectively detect various defects such as spots, scratches, fibers and dirt, and the false-positive rate of defects has been reduced by half. The resampling-based Fourier transform speeds up the computational process and the FPGA parallel acceleration architecture is three times faster than comparable server CPUs, reducing the scan detection time of the entire 8.5-generation LCD panel to 8.5 s.

One-electron spectra and susceptibilities of the three-dimensional electron gas from self-consistent solutions of Hedin's equations

A few approximate schemes to solve the Hedin equations self-consistently introduced in (Phys. Rev. B 94, 155101 (2016)) are explored and tested for the 3D electron gas at metallic densities. We calculate one electron spectra, dielectric properties, compressibility, and correlation energy. Considerable reduction in the calculated band width (as compared to the self consistent GW result) has been found when vertex correction was used for both polarizability and self energy. Generally, it is advantageous to obtain the diagrammatic representation of polarizability from the definition of this quantity as a functional derivative of the electronic density with respect to the total field (external plus induced). For self energy, the first order vertex correction seems to be sufficient for the range of densities considered. Whenever it is possible, we compare the accuracy of our vertex-corrected schemes with the accuracy of the self-consistent quasi-particle GW approximation (QSGW), which is less expensive computationally. We show that QSGW approach performs poorly and we relate this poor performance with an inaccurate description of the screening in the QSGW method (with an error comprising a factor 2-3 in the physically important range of momenta).

Experimental validation of acoustic intensity bandwidth extension by phase unwrapping.

The phase and amplitude gradient estimator (PAGE) method for active acoustic intensity uses pairwise microphone transfer functions to obtain the phase gradient, which improves the calculation bandwidth over the traditional weighted quadspectral method. Additionally, for broadband sources, the PAGE theory indicates that the transfer function phase can be unwrapped to further extend the usable frequency range to beyond the spatial Nyquist frequency. Here, two experiments demonstrate intensity bandwidth extension by more than an order of magnitude using phase unwrapping. First, plane-wave tube results show accurate one-dimensional intensity calculations with the microphones separated by five wavelengths, 30 times the traditional limit. Second, two-dimensional measurements of a laboratory-scale jet with a four-microphone probe yield physically reasonable calculations at frequencies 15 times the traditional limit.

Electronic structure of Na, K, Si, and LiF from self-consistent solution of Hedin's equations including vertex corrections

A few self-consistent schemes to solve the Hedin equations are presented. They include vertex corrections of different complexity. Commonly used quasiparticle approximation for the Green function and static approximation for the screened interaction are avoided altogether. Using alkali metals Na and K as well as semiconductor Si and wide gap insulator LiF as examples, it is shown that both the vertex corrections in the polarizability P and in the self energy $\Sigma$ are important. Particularly, vertex corrections in $\Sigma$ with proper treatment of frequency dependence of the screened interaction always reduce calculated band widths/gaps, improving the agreement with experiment. The complexity of the vertex included in P and in $\Sigma$ can be different. Whereas in the case of polarizability one generally has to solve the Bethe-Salpeter equation for the corresponding vertex function, it is enough (for the materials in this study) to include the vertex of the first order in the self energy. The calculations with appropriate vertices show remarkable improvement in the calculated band widths and band gaps as compared to the self-consistent GW approximation as well as to the self-consistent quasiparticle GW approximation.

A comparative density functional theory study of electronic structure and optical properties of -aminobutyric acid and its cocrystals with oxalic and benzoic acid

Abstract In this letter, we study the electronic structure and optical properties of the active medicinal component γ -aminobutyric acid (GABA) and its cocrystals with oxalic (OXA) and benzoic (BZA) acid by means of the density functional theory formalism. It is shown that the cocrystallization strongly weakens the zwitterionic character of the GABA molecule leading to striking differences among the electronic band structures and optical absorption spectra of the GABA crystal and GABA:OXA, GABA:BZA cocrystals, originating from distinct sets of hydrogen bonds. Calculated band widths and Δ -sol band gap estimates indicate that both GABA and GABA:OXA, GABA:BZA cocrystals are indirect gap insulators.

Ag(001) 표면 위에 놓인 Fe 선의 자성과 전자구조

The electronic structure and magnetism of Fe chain along the [110] direction on Ag(001) were investigated by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within generalized gradient approximation (GGA). The magnetic moment of Fe atom in Fe chain is calculated to be , which is slightly larger than that () of the Fe[110] chain on Cu(001). The reduced coordination number for the Fe chain induced the Fe-d band narrowing and exchange-splitting enhancement, which are responsible for the large magnetic moment of the Fe chain. The calculated band width of the Fe-d band and the exchange-splitting are 1.7 eV and 3.2 eV, respectively.

Preparation of metallic BEDT-TTF charge transfer complex of 3,3′,5,5′-tetranitro-4,4′-biphenyldiol dianion (TNBP2−) having flexible molecular shape

Two kinds of 3,3′,5,5′-tetranitro-4,4′-biphenyldiol dianion (TNBP2−) molecules having different dihedral angles (φ) between the two phenyl rings exist in the tetrabutylammonium salt of TNBP2− (φ = 0° and 35°), while only one kind of TNBP2− molecule exists in the tetraphenylphosphonium salt (φ = 0°). The 4∶1 cation radical salt of BEDT-TTF (ET) with TNBP2− asa counter anion is metallic down to 3 K. The ET molecules form a two-dimensional conducting layer which is sandwiched by the layers of flat TNBP2− molecules (φ = 0°). The crystal structure indicates the β″432-type stacking of tetramerized ET molecules which is caused by hydrogen bonds between the CH groups of ET and the oxygen atoms (nitro and phenol) of TNBP2−. The optical spectra in a KBr pellet are consistent with both the highly conductive and distorted structural nature. The magnetic susceptibility at room temperature is high (χ = 6.7 × 10−4 emu spin−1) compared with the conventional organic metal based on ET (χ = 3.4–5.5 × 10−4 emu spin−1) indicating strong electron correlation in the 4∶1 complex. The temperature dependence of the magnetic susceptibility suggests a semimetallic nature which is consistent with the calculated Fermi surface. The calculated band width is comparable to the estimated effective on-site Coulomb repulsive energy. A semiconductive behavior with high conductivity is observed in the nearly 2∶1 ET complex of TNBP2−. A partial charge transfer state of the ET molecules is supported by the optical spectra. The high conductivity and optical data suggest that the 2∶1 salt is not (ET1+)2(TNBP2−) but most plausibly (ET0.5+)2(HTNBP1−).

Spin- and k-dependent electronic structure of ferromagnetic nickel

We have measured the spin- and angle-resolved photoemission spectra of ferromagnetic Ni(110) and determined the spin-dependent energy-dispersions along the Γ-K-X direction of the Brillouin zone. We have observed the exchange-split band dispersions and assigned the bands to s -like Σ 1 band and d -like Σ 1 , Σ s and Σ 4 bands in Γ-K region and S 1 , S 2 and S 4 bands in K-X region. Comparing the observed results with the theoretical LDA band calculation, we found that the width of d -band is narrower than the calculated band width. The narrowing in the majority spin band is larger than in the minority spin band. It is shown that the electron correlation in the majority spin band is much stronger than in the minority spin band. We also found that the observed values of the exchange splitting are much smaller than the calculated values.

Spin- and k-dependent electronic structure of ferromagnetic nickel

We have measured the spin- and angle-resolved photoemission spectra of ferromagnetic Ni(110) and determined the spin-dependent energy-dispersions along the Γ-K-X direction of the Brillouin zone. We have observed the exchange-split band dispersions and assigned the bands to s-like Σ 1 band and d-like Σ 1, Σ s and Σ 4 bands in Γ-K region and S 1, S 2 and S 4 bands in K-X region. Comparing the observed results with the theoretical LDA band calculation, we found that the width of d-band is narrower than the calculated band width. The narrowing in the majority spin band is larger than in the minority spin band. It is shown that the electron correlation in the majority spin band is much stronger than in the minority spin band. We also found that the observed values of the exchange splitting are much smaller than the calculated values.

Electronic structure of bis [1,2,5]thiadiazolo- p-quinobis (1,3-dithiole) (BTQBT) studied by ultraviolet photoemission spectroscopy

Ultraviolet photoemission spectroscopy (UPS) has been used to investigate the electronic structure of the unusually high conductive organic compound, bis [1,2,5]thiazolo- p-quinobis(1,3-dithiole) (BTQBT). The observed spectral features were analyzed with the aid of the semiempirical MNDO-SCF-MO (modified neglect of diatomic overlap self-consistent field molecular orbital) method. BTQBT shows a low photoionization threshold of 4.57 eV in the solid state as compared with the gas phase value of 6.4 eV which is evaluated from the oxidation potential. This lowering from the gas phase can be explained with respect to the strong intermolecular interactions: if we take the calculated band width of 0.7 eV, the polarization energy and the other solid state effects of about 1.5 eV contribute to this lowering. The work function of BTQBT was found to be 4.3 eV. From this value and the ionization threshold energy, the energy difference between the Fermi level and the top of the valence band is determined to be 0.3 eV. This small value, in agreement with the observed activation energy in electric conduction, should be at least part of the origin of the high conductivity in BTQBT. These observations show that the strong intermolecular interaction in the solid state of BTQBT, suggested from the crystal structure of this compound, is essential for the high conductivity of this compound

Vibrational relaxation and frequencies of liquid molecules. II. Comparison of theoretical and experimental results

The Raman isotropic band widths and the peak frequencies of totally symmetric vibrational modes were measured for the CH 3I, CD 3I, CH 3Br, and CHCl 3 molecules in liquid phases at various temperatures. The integrated intensities of the Raman scattering and the infrared absorption of the fundamental and overtone bands were measured to obtain the intensity parameters required for calculating the band widths and the gas-to-liquid shifts of the frequency by the theory reported in part I. The agreement between the calculated and the observed values is reasonably good. The phase modulation was the dominant process both in the band broadening and in the frequency shift. It was pointed out, for the first time, that the cross term between the attractive and the repulsive parts of the mechanical collision potential played an important role in the band broadening. Without the cross term, the calculated band widths of the ν CH and δ HCH modes would be an order of magnitude larger than the observed widths.

Closed-shell crystal orbital calculations on columnar stacks of conjugated macrocyclic ligands

Closed-shell π -electron crystal orbital calculations with the Hückel and SCFPPP methods (as modified by Ladik) have been performed for eleven macrocyclic conjugated molecules placed in perfect columnar stacks at a separation of 0.373 nm. The results from both methods correlate well with each other, and the calculated band widths indicate that the band model is only applicable at, or below the above-mentioned spacing for exactly superimposed molecules. The crude calculated band gaps are (as expected) unsatisfactory, and recommended methods have been used to improve them.

An Investigation of the Electronic Structure of GaSe and GaTe by Photoelectron Spectroscopy, Using a Synchrotron Source, and Electron Energy Loss Spectroscopy

AbstractThe valence band structure as well as the location of the Ga 3d levels have been investigated for vacuum cleaved GaSe and GaTe single crystals by photoelectron spectroscopy using a synchrotron source. In addition the conduction band structure has been probed by photoemission partial yield spectroscopy and by electron energy, loss spectroscopy. The experimental results are in reasonable agreement with theoretical predictions although calculated band widths are generally too narrow. A feature in the partial yield and electron loss spectra is tentatively interpreted in terms of surface states.

Influence of Plasmons on X‐Ray Emission Bands of Some Simple Metals

AbstractThe appearance of plasmon satellites in the X‐ray emission spectra should give rise to a reduction in free electron conduction band widths according to the intensity conservation rule. A simple method is suggested to study this reduction by modifying the Sommerfeld formula for the phase space available to the single‐particle excitations and the effective electronic mass due to the existence of the plasmons. It is found that the calculated band widths agree fairly well with corresponding experimental values for some simple metals. The inclusion of the exchange and correlations, however, removes the agreement between the theoretical and experimental values of the band width. This is attributed to the fact that the long‐ and short‐wavelength tails are avoided in experimental measurements, whereas their effects are included in the exchange and correlation corrections.

Band structure and transport of charge carriers in metal-free phthalocyanine

The band structures for an excess electron and an excess hole in the metal-free phthalocyanine crystal were calculated in the tight binding approximation. The LCAO wave functions for the cation and anion radicals were calculated by the unrestricted SCF method. The Goeppert-Mayer-Sklar type potential was used as an average potential. Simplified formulas were derived for the calculation of the resonance penetration integrals between carbon and nitrogen atoms. The calculated band width was of the order of 10-2 ev for an electron and 10-3 ev for a hole. The calculation predicted the large anisotropy of the mobility tensor of an excess electron.