Orbital Energy Spectra Research Articles

Reliability Evaluation of Superluminescent Diodes in Space Environment Based on Bayesian Networks

Reliability evaluation of electronic systems in space environment is a critical issue. In this work, reliability evaluation of superluminescent diode (SLD) systems, which are sensitive to both displacement damage effects and charge–discharge effects, was investigated by the Bayesian network model. Displacement equivalence model of the SLDs is verified by the irradiation results of 5-MeV protons and 1-MeV electrons. Charge–discharge effects of SLDs are induced by 110-keV electrons. Orbital energy spectra and cumulative distribution functions for the equivalent irradiation fluence are calculated by self-built software. Based on the experimental and calculated results, the Bayesian networks under various conditions are established. The probabilities of the type of faults prone in the system under each condition can then be analyzed and quantified. The proposed method provides a good idea for on-orbit reliability evaluation of complex systems.

The inner oxygen-substituted strategy effects on structure, aromaticity and absorption spectra of corrole isomers: A theoretical study

Corrole and oxaporphyrin have been successfully synthesized and applied in many research fields such as organic photoelectronics and sensors with the unique photophysical and chemical properties. However, the low synthesis yields of oxacorrole drive researchers turning their attention to theoretical studies for more reasonable molecular structure as the appeal of energy conservation and green chemistry. Corroles, oxacorroles (OC) and dioxacorroles (DOC), a total of 14 molecules, are calculated to systematically explore their structures, intramolecular hydrogen bonds, molecular aromatic and absorption spectral properties influenced by the inner O atoms positions with density functional theory (DFT) and time-dependent density functional theory (TDDFT). The smaller NICS(1)ZZ values of oxacorrole (−35.23 ppm to −33.54 ppm) and dioxacorrole (−34.91 ppm to −33.24) than these of corroles (−32.97 ppm and −33.12 ppm) indicate that the O atoms attendances can increase the molecular aromaticity. The gradually increasing energy gaps of H-8 to H-3 from Corrole1 and Corrole2 to DOC series and the larger charge of CO (+0.208e—+0.380e) than that of CN (+0.065e—+0.177e) illustrate that the substitution of O can reduce the degeneracy degree of energy levels and change the charge distributions. With Hirshfeld method, the molecular orbital contributions of H-1, HOMO, LUMO and L+1 exhibit the regular effects of O atoms positions on orbital energy and electron absorption spectra. For series 1, 23O is beneficial to the red shift of electron absorption spectra. These theoretical conclusions manifest that OC1-23 and DOC1-1 possess the excellent absorption characteristics in the visible region, which can be used as potential materials in the fields of photoelectric materials.

Investigation of chemical bonding and electronic network of rGO/PANI/PVA electrospun nanofiber

Reduced graphene oxide-reinforced polyaniline and poly(vinyl alcohol) (PVA/PANI/rGO) nanofibers were synthesized by electrospinning method with different rGO content varying from 1 to 5wt%. The PVA/PANI/rGO nanofibers were characterized by SEM, FTIR, Raman, XPS and UV–visible spectroscopy to investigate the morphology, vibrational bonding, elemental composition and optical properties, respectively. The XRD results reveal the broad peak at 2θ = 25° corresponding to (002) for rGO and three peaks at 2θ = 14°, 20° and 25° corresponding to (011), (020) and (200), respectively for PANI. The FTIR signatures at 1088, 1245, 1359, 1411, 1717, 2930 and 3305 cm−1 correspond to ν-(C–O), ν-(N–H), ν-(C–OH), ν-(C=O), ν-(C–H) and ν-(O–H), respectively. The optical bandgap of PVA/PANI/rGO nanofibers was decreased from 4.20 to 4.07 eV as the rGO wt% increased. The structural and electronic network of carbon was analyzed by semiempirical Gaussian peaks to predict various binding energy of core orbital binding energy spectra in PVA/PANI/rGO nanofibers.

The Synchrotron Emission Pattern of Intrabinary Shocks

Abstract We model millisecond pulsar winds colliding with radiatively driven companion winds in black widow and redback systems. For the redbacks, the geometry of this intrabinary shock (IBS) is quite sensitive to the expected equatorial concentration in the pulsar outflow. We thus analytically extend IBS thin-shock models to pulsar winds. We compute the synchrotron emission from such shocks, including the buildup and cooling of the particle population as it accelerates along the IBS. For reasonable parameters, this IBS flux dominates the binary emission in the X-ray band. The modeling shows subtle variation in spectrum across the IBS peak, accessible to sensitive X-ray studies. As example applications, we fit archival CXO/XMM data from the black widow pulsar J1959+2048 and the redback PSR J2339–0533, finding that the model reproduces well the orbital light-curve profiles and energy spectra. The results show a very hard injected electron spectrum, indicating likely dominance by reconnection. The light-curve fitting is sensitive to the geometric parameters, including the very important orbital inclination i. Coupled with optical fits of the companion star, such IBS X-ray light-curve modeling can strongly constrain the binary geometry and the energetics of the millisecond pulsar wind.

Comparison of Green’s functions for transition metal atoms using self-energy functional theory and coupled-cluster singles and doubles (CCSD)

We demonstrate in the present study that self-consistent calculations based on the self-energy functional theory (SFT) are possible for the electronic structure of realistic systems in the context of quantum chemistry. We describe the procedure of a self-consistent SFT calculation in detail and perform the calculations for isolated 3d transition metal atoms from V to Cu as a preliminary study. We compare the one-particle Green's functions obtained in this way and those obtained from the coupled-cluster singles and doubles method. Although the SFT calculation starts from the spin-unpolarized Hartree-Fock state for each of the target systems, the self-consistency loop correctly leads to degenerate spin-polarized ground states. We examine the spectral functions in detail to find their commonalities and differences among the atoms by paying attention to the characteristics of the two approaches. It is demonstrated via the two approaches that calculations based on the density functional theory (DFT) can fail in predicting the orbital energy spectra for spherically symmetric systems. It is found that the two methods are quite reliable and useful beyond DFT.

X-Ray Timing Analysis of Cyg X-3 Using AstroSat/LAXPC: Detection of Milli-hertz Quasi-periodic Oscillations during the Flaring Hard X-Ray State

Abstract We present here results from the X-ray timing and spectral analysis of the X-ray binary Cyg X-3 using observations from the Large Area X-ray proportional Counter on board AstroSat. Consecutive light curves observed over a period of one year show the binary orbital period of 17253.56 ± 0.19 s. Another low-amplitude, slow periodicity of the order of 35.8 ± 1.4 days is observed, which may be due to the orbital precession as suggested earlier by Molteni et al. During the rising binary phase, power density spectra from different observations during the flaring hard X-ray state show quasi-periodic oscillations (QPOs) at ∼5–8 mHz, ∼12–14 mHz, and ∼18–24 mHz frequencies at the minimum confidence of 99%. However, during the consecutive binary decay phase, no QPO is detected up to 2σ significance. Energy-dependent time-lag spectra show soft lag (soft photons lag hard photons) at the mHz QPO frequency and the fractional rms of the QPO increases with the photon energy. During the binary motion, the observation of mHz QPOs during the rising phase of the flaring hard state may be linked to the increase in the supply of the accreting material in the disk and corona via stellar wind from the companion star. During the decay phase, the compact source moves in the outer wind region causing the decrease in supply of material for accretion. This may cause weakening of the mHz QPOs below the detection limit. This is also consistent with the preliminary analysis of the orbital phase-resolved energy spectra presented in this paper.

Dominant Carbons in trans- and cis-Resveratrol Isomerization.

A comprehensive analysis for isomerization of geometric isomers in the case of resveratrol (R) has been presented. As an important red wine molecule, only one geometric isomer of resveratrol, i.e., trans-R rather than cis-R, is primarily associated with health benefit. In the present study, density function theory (DFT) provides accurate descriptions of isomerization of resveratrol. The nearly planar trans-R forms a relatively rigid and less flexible conjugate network, but the nonplanar cis-R favors a more flexible structure with steric through space interaction. The calculated carbon nuclear magnetic resonance (NMR) chemical shift indicates that all carbons are different in the isomers; it further reveals that four carbon sites, i.e., C(6), C(8)═C(9), and C(11), have a significant response to the geometric isomerization. Here C(6) is related to the steric effect in cis-R, whereas C(11) may indicate the isomerization proton transfer on C(9) linking with the resorcinol ring. The excess orbital energy spectrum (EOES) confirms the NMR "bridge of interest" carbons and reveals that five valence orbitals of 34a, 35a, 46a, 55a, and 60a respond to the isomerization most significantly. The highest occupied molecular orbital (HOMO), 60a, of the isomer pair is further studied using dual space analysis (DSA) for its orbital momentum distributions, which exhibit p-electron dominance for trans-R but hybridized sp-electron dominance for cis-R. Finally, energy decomposition analysis (EDA) highlights that trans-R is preferred over cis-R by -4.35 kcal·mol-1, due to small electrostatic energy enhancement of the attractive orbital energy with respect to the Pauli repulsive energy.

On the errors of local density (LDA) and generalized gradient (GGA) approximations to the Kohn-Sham potential and orbital energies.

In spite of the high quality of exchange-correlation energies Exc obtained with the generalized gradient approximations (GGAs) of density functional theory, their xc potentials vxc are strongly deficient, yielding upshifts of ca. 5 eV in the orbital energy spectrum (in the order of 50% of high-lying valence orbital energies). The GGAs share this deficiency with the local density approximation (LDA). We argue that this error is not caused by the incorrect long-range asymptotics of vxc or by self-interaction error. It arises from incorrect density dependencies of LDA and GGA exchange functionals leading to incorrect (too repulsive) functional derivatives (i.e., response parts of the potentials). The vxc potential is partitioned into the potential of the xc hole vxchole (twice the xc energy density ϵxc), which determines Exc, and the response potential vresp, which does not contribute to Exc explicitly. The substantial upshift of LDA/GGA orbital energies is due to a too repulsive LDA exchange response potential vxresp (LDA) in the bulk region. Retaining the LDA exchange hole potential plus the B88 gradient correction to it but replacing the response parts of these potentials by the model orbital-dependent response potential vxresp (GLLB) of Gritsenko et al. [Phys. Rev. A 51, 1944 (1995)], which has the proper step-wise form, improves the orbital energies by more than an order of magnitude. Examples are given for the prototype molecules: dihydrogen, dinitrogen, carbon monoxide, ethylene, formaldehyde, and formic acid.

Density functional study on the effect of aromatic rings flanked by bithiophene of novel electron donors in small-molecule organic solar cells

In order to further improve the short-circuit current (JSC) and the overall performance of the already synthesized donor molecule (1s) used in organic heterojunction solar cells, six new A-A-D-A-A type small molecules composed of different donor (D, electron rich) and same acceptor (A, electron poor) moieties were designed and characterized by using density functional theory (DFT), time-dependent density functional theory (TD-DFT) and Marcus theory. Through calculating frontier molecular orbital energy levels and spectra properties, we found that HOMO level goes up while Eg goes down along with the cycle extension of the center part flanked by bithiophene. Next, character of excited state, ionization potentials (IPs) and charge transport properties were also investigated to provide an in-depth insight into the charge transfer/transport characteristics and the JSC of organic solar cells. The results reveal that compounds 3c, 3n and 3° exhibit favorable JSC and comparable performance to original molecule (1s) and show promising potential in organic solar cells.

Benchmarking the Bethe-Salpeter Formalism on a Standard Organic Molecular Set.

We perform benchmark calculations of the Bethe–Salpeter vertical excitation energies for the set of 28 molecules constituting the well-known Thiel’s set, complemented by a series of small molecules representative of the dye chemistry field. We show that Bethe–Salpeter calculations based on a molecular orbital energy spectrum obtained with non-self-consistent G0W0 calculations starting from semilocal DFT functionals dramatically underestimate the transition energies. Starting from the popular PBE0 hybrid functional significantly improves the results even though this leads to an average −0.59 eV redshift compared to reference calculations for Thiel’s set. It is shown, however, that a simple self-consistent scheme at the GW level, with an update of the quasiparticle energies, not only leads to a much better agreement with reference values, but also significantly reduces the impact of the starting DFT functional. On average, the Bethe–Salpeter scheme based on self-consistent GW calculations comes close to the best time-dependent DFT calculations with the PBE0 functional with a 0.98 correlation coefficient and a 0.18 (0.25) eV mean absolute deviation compared to TD-PBE0 (theoretical best estimates) with a tendency to be red-shifted. We also observe that TD-DFT and the standard adiabatic Bethe–Salpeter implementation may differ significantly for states implying a large multiple excitation character.

Molecular structure and electronic properties of pyridylindolizine derivative containing phenyl and phenacyl groups: Comparison between semi-empirical calculations and experimental studies

This work deals with theoretical investigations of a pyridylindolizine derivative containing phenyl and phenacyl groups, namely [1-benzoyl-2-phenyl-7-(pyridin-4-yl)indolizin-3-yl](4-methoxyphenyl)methanone (C34H24N2O3), and comparison of modeling results with available experimental data (e.g. X-ray-structure analysis). The molecular modeling has been performed by means of AM1, MNDO, PM3 and RM1 semi-empirical methods. The deviation between experimental and calculated parameters has been ascertained in terms of average relative error, ARE (%). The calculated geometries, after comparisons with corresponding X-ray structure, have pointed out that RM1 and PM3 predict better the bond lengths than other semi-empirical methods, exhibiting the average relative errors of 4.529% and 4.680%, respectively. The best model for the prediction of interatomic angles is AM1 method, revealing a deviation error of 1.067% from the observed angles determined by X-ray structure analysis. Likewise, the theoretical vibrational and electronic spectra have been calculated and reported. In addition, the optimized structures, binding energies, atomic charges, molecular orbital energy spectra, the electrostatic potential as well as the quantitative structure activity relationship (QSAR) properties of the molecule have been computed and discussed.

Aufbau derived from a unified treatment of occupation numbers in Hartree–Fock, Kohn–Sham, and natural orbital theories with the Karush–Kuhn–Tucker conditions for the inequality constraints ni≤1 and ni≥

In the major independent particle models of electronic structure theory-Hartree-Fock, Kohn-Sham (KS), and natural orbital (NO) theories-occupations are constrained to 0 and 1 or to the interval [0,1]. We carry out a constrained optimization of the orbitals and occupation numbers with application of the usual equality constraints summation (i) (infinity) n(i)=N and phi(i)/phi(j)=delta(ij). The occupation number optimization is carried out, allowing for fractional occupations, with the inequality constraints n(i)>or=0 and n(i)<or=1 with the Karush-Kuhn-Tucker method. This leads in all cases to an orbital energy spectrum with (only for NO and KS) possibly fractionally occupied degenerate levels at energy equal to the Lagrange multiplier varepsilon for the first equality constraint, completely occupied levels at lower energies and completely unoccupied levels at higher energies. Aufbau thus follows in all cases directly from this general derivation.

Electronic Structure of Gallium, Copper, and Nickel Complexes of Corrole. High-Valent Transition Metal Centers versus Noninnocent Ligands

Using regular nonlocal density functional theory (DFT) as well as combined DFT and configuration interaction calculations, we have carried out a first theoretical study of the electronic structure of metallocorroles. The valence orbital energy spectra and the calculated electronic absorption spectrum of (Cor)Ga (Cor3- = corrolato), a prototype non-transition-metal corrole, are qualitatively similar to those of a metalloporphyrin such as zinc porphyrin. The “four-orbital model” holds well for corroles. The a2 and b1 HOMOs of (Cor)Ga are crude analogues of the well-known a1u and a2u porphyrin HOMOs, respectively. Thus, as in the case of porphyrins, there are two nearly equienergetic π-cation radical states for corroles. DFT also appears to provide a good description of the stabilization of high-valent transition-metal centers and of ligand noninnocence, two intertwined and central themes in metallocorrole chemistry. The calculated ground state of (Cor)Cu is a diamagnetic d8 Cu(III) state, with Cu(II) π-cati...

Measured radiation damage in charge coupled devices exposed to simulated deep orbit proton fluxes

Measurements were made to quantify the effects of radiation damage in large area, deep-depletion CCDs developed for the joint European X-ray telescope (JET-X). Two devices were tested — the first, a standard X-ray CCD and the second, otherwise identical, including supplementary buried channels to improve its radiation hardness. Both devices were exposed to the expected in-orbit proton fluxes at the proton irradiation facility (PIF) at the Paul Scherrer Institute. The experimental conditions included the predicted orbital energy spectrum, its evolution and the proposed JET-X proton shielding. Energy resolution and charge transfer efficiency were measured after exposure to incremental doses corresponding to 0.25, 0.5, 1, 2 and 5 years in orbit. The radiation-hard device performed substantially better than the conventional device, showing a 20% degradation in energy resolution after 5 years equivalent dose (corresponding to ∼ 10 9 protons cm −2), as compared to ∼ 60% for the conventional device. Finally, the devices were exposed to fluences appropriate to the August 1972 solar flare. These results have been used to develop a model to predict the fwhm energy resolution of radiation damaged CCD.

Electronic and lattice structures in potassium-doped stage-1 polyacetylene

Interchain transfers (ICTs) via dopants and interchain Coulomb (ICC) and dopant Coulomb (DC) potentials in a Thomas-Fermi approximation are calculated in a stoichiometrically K-doped stage-1 polyacetylene ((CH) x ). Owing to the large sizes of the valence orbitals of K, dopants give the most important and dense net of ICTs. We make Hartree-Fock calculations to see their effects using a reasonable intrachain Hamiltonian. ICTs slightly affect the intrachain states but greatly change the orbital energy spectrum though there is only a small effect near the Fermi energy. The DC converts the BOW charged soliton lattice into a CDW bipolaron lattice. The ICC enlarges the gap and makes the phases of the bipolaron lattices ordered. Highly K-doped (CH) x has a gap and lattice distortions similar to those of charge soliton lattices. Electron correlation is essential to achieve metallic (CH) x .

Coincidence electron-scattering experiments: the statistics of coincidence counting

A new coincidence electron-scattering spectrometer for electron momentum spectroscopy (EMS) experiments is described. The new features include the use of a single 360° cylindrical mirror analyzer (CMA) for energy analysis and a coincidence data acquisition system based on a qVt-multichannel analyser and CAMAC electronics. The CMA energy resolution and coincidence time resolution are 0.32 ± 0.03% ΔE/E fwhm and 3.5 ± 0.5 ns fwhm, respectively. The helium 1s orbital binding energy spectrum is obtained at 1000 eV binding energy and 100 eV pass energy, yielding a coincidence binding energy resolution of 1.5 ± 0.2 eV fwhm. The coincidence data analysis procedure that is introduced provides experimental verification of some basic statistics of coincidence counting.

The Fock space coupled cluster method: theory and application

The Fock space coupled cluster method and its application to atomic and molecular systems are described. The importance of conserving size extensivity is demonstrated by the electron affinities of the alkali atoms. Two types of intruder states are discussed, one attributable to the orbital energy spectrum and the other caused by two-electron interactions. They are illustrated by the excited states of Li2 and by1S states of Be, respectively. It is shown how both problems may be solved using incomplete model spaces. The selection of the model space in a moderately dense spectrum is discussed in connection with N2 excited states.

Orbital SCF energies in the double proton transfer of the adenine-thymine base pair

The double-minimum potential generated by the proton motion involved in the two hydrogen bonds of the adenine-thymine base pair can be accounted for through the orbital-energy spectrum. The results show that the greatest interaction between the molecular orbitals is found when the interprotonic distance of the protons is optimum,i.e. at the top of the barrier of the double-minimum potential. This raises the question of charge transfer electronic transitions as a possibility of modelling the behaviour of the double proton transfer in the excited states of this base pair.

On the orbital energy spectrum of CO adsorbed on Ni(001)

A localised orbital method has been used to calculate the orbital energy level spectrum for CO adsorbed in a c(2*2) array on a thin Ni crystal. The adsorption geometry is that reported by Andersson and Pendry (1977). The results reveal 4 sigma - and 5 sigma -like bands each approximately 0.7 eV wide centred 10.0 and 4.9 eV below EF respectively and a 1 pi -like band >2.0 eV wide centred approximately 7 eV below EF and overlapping the 5 sigma band.

Theoretical orbital energy spectra of electrons in chemisorbed systems: Chalcogens on Ni(001)

Theoretical energy level spectra calculated by the localised orbital pseudopotential method are presented for chemisorbed O, S, Se and Te monolayers on Ni(001). Adsorption-induced features are a band of bonding states 2–3 eV wide centred ≈ 4 eV below E f and a band of states centred near E f. Supporting experimental evidence is discussed.