Total Electronic Charge Research Articles

Electrons charge concentration and melting point of bcc metals

The study presents a new method to determine the melting point of bcc metals. The method uses unit cell parameters and the atomic number Z of the chemical element. Based on these data, one can calculate the total charge of electrons belonging to a single atom and volume V of the space occupied by the atom. The value of Ζ/V (average charge electron density in a volume occupied by the atom) is proportional to the melting point of metals with the bcc lattice (Tbcc). Taking into account the number of atoms per bcc unit cell, a suitable model has been proposed. Calculations made with the use of this model show good agreement with literature data.

Study on kinetic energy of a novel metal composite for anode catalyst in direct methanol fuel cell

Summary Platinum (Pt) is the most commonly used catalyst in fuel cell systems because of its high efficiency. However, pure Pt is poisoned by carbon monoxide, which is an intermediate reaction product in fuel cell systems. Although PtRu alloys are considered to be promising anodic catalysts for commercial direct methanol fuel cells (DMFC), they are limited by slow reaction kinetics, which reduces the performance of the fuel cells and increases cost. Thus, the main objective of this study is to investigate the addition of potential metals to PtRu, specifically, nickel, Ni, and iron, Fe, to improve the reaction kinetics. This study analyzes the nano-catalyst structures using Materials Studio DMol3. The adsorption energy, free energy, vibrational frequencies and total electronic charge density were also calculated as a function of ground-state properties using the density functional theory (DFT). The simulation results indicate that PtRuNiFe has the potential to improve the performance of the catalyst due to the lower calculated adsorption energies and the presence of Fe2+ and Ni2+ ions, which increases the electron density. Finally, this study concludes that PtRuFeNi/multi-walled carbon nanotube (MWCNT) shows a comparable performance to PtRu. However, it is observed that PtRuFeNi/MWCNT is more stable and has a higher reaction rate than PtRu. Copyright © 2014 John Wiley & Sons, Ltd.

The Study of Gold Nanoparticles in basis of Slater Functions

The electronic structure of the gold nanoparticles were investigated by semi-empirical Wolfsberg - Helmholz method. This is a variant of the molecular orbitals method. Molecular orbitals are represented as a linear combination of valence atomic orbitals of the atoms of the nanoparticle. As the atomic orbitals used 6s-, 6p -, 6p - and 6p - y z x Slater atomic orbitals of gold atoms. The exponential parameters of Slater functions were calculated and defined the analytic expression of the basis functions. The numerical values of the unknown coefficients of the linear combination are found by solution of equations of molecular orbitals method. Calculations were carried out with own computer program. The orbital energies, potential ionization, the total electronic energy and effective charge of atoms of gold nanoparticles were calculated. The results indicate that the gold nanoparticles are soft, electrophile and conductive material.

Response of the imaging plates to the electron beams from a linear accelerator at ultra-low intensity

The response of the imaging plate (IP) as a two-dimensional irradiation dose monitor of high-energy electrons has been investigated. The Co-60 γ-ray irradiation facilities and the 16 MeV S-band electron linear accelerator (linac) in Radiation Research Center, Osaka Prefecture University have been used for the experiments. From the results of the irradiation experiments with γ-rays uniform response of IP over the plate and linear response to the exposure have been obtained. Thermoluminescence dosimeter has been used to determine the exposure. The ultra-low intensity electron beams developed have been used. The results of the irradiation experiments with the narrow electron beams from the linac at an energy of 8 MeV have shown the linear response of IP to the total electron charge for irradiation. By the broad beam an IP image of a model sample has been obtained showing the characteristic scattering behavior of high-energy electrons. These results have shown the applicability of IP to monitoring two-dimensional dose distribution of electrons.

Effect of chirp on self-modulation and laser wakefield electron acceleration in the regime of quasimonoenergetic electron beam generation

Strongly self-modulated regime of laser wakefield electron acceleration has been experimentally studied using positively/negatively chirped Ti:sapphire laser pulses with duration $\ensuremath{\ge}45\text{ }\text{ }\mathrm{fs}$, and intensity $\ensuremath{\le}1.2\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ interacting with a plasma having density $>5\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$. The total charge of the high energy electrons produced from self-injection and acceleration in the wakefield was found to depend strongly and asymmetrically on the magnitude and sign of the chirp, which was also corroborated by the forward Raman scattering signals. Generation of low divergence ($\ensuremath{\le}10\text{ }\text{ }\mathrm{mrad}$), quasimonoenergetic electron beam was observed with a maximum energy of $\ensuremath{\sim}28\text{ }\text{ }\mathrm{MeV}$ for a positively chirped laser pulse of duration $\ensuremath{\sim}70\text{ }\text{ }\mathrm{fs}$. The observations are explained considering faster rise time associated with a positive chirped laser pulse which generates intense seed for stronger modulation of the laser pulse and consequently stronger wakefield excitation leading to higher electron beam charge and energy.

Bright betatron X-ray radiation from a laser-driven-clustering gas target

Hard X-ray sources from femtosecond (fs) laser-produced plasmas, including the betatron X-rays from laser wakefield-accelerated electrons, have compact sizes, fs pulse duration and fs pump-probe capability, making it promising for wide use in material and biological sciences. Currently the main problem with such betatron X-ray sources is the limited average flux even with ultra-intense laser pulses. Here, we report ultra-bright betatron X-rays can be generated using a clustering gas jet target irradiated with a small size laser, where a ten-fold enhancement of the X-ray yield is achieved compared to the results obtained using a gas target. We suggest the increased X-ray photon is due to the existence of clusters in the gas, which results in increased total electron charge trapped for acceleration and larger wiggling amplitudes during the acceleration. This observation opens a route to produce high betatron average flux using small but high repetition rate laser facilities for applications.

Ground State of the Asymmetric Anderson Model

The ground state of the asymmetric Anderson model is studied by the perturbation theory with respect to the s-d mixing integral. The ground state energy is calculated exactly to the third dominant order of its perturbation series in the limit of small values of Δ/D, where Δ and D are the width of the d-level and of the conduction band, respectively. The number of the d-electrons, the spin and charge susceptibilities are calculated to their second dominant order. The total localized charge of the conduction electrons is shown to vanish. The magnetoresistance is then calculated, and is found to be negative in a weak magnetic field.

Generation of 500 MeV–1 GeV energy electrons from laser wakefield acceleration via ionization induced injection using CO2 mixed in He

Laser wakefield acceleration of 500 MeV to 1 GeV electron bunches has been demonstrated using ionization injection in mixtures of 4% to 10% of CO2 in He. 80 TW laser pulses were propagated through 5 mm gas jet targets at electron densities of 0.4−1.5×1019cm−3. Ionization injection led to lower density thresholds, a higher total electron charge, and an increased probability of producing electrons above 500 MeV in energy compared to self-injection in He gas alone. Electrons with GeV energies were also observed on a few shots and indicative of an additional energy enhancement mechanism.

Quantum topology phase diagrams for molecules, clusters, and solids

AbstractThe need to make more quantitative use of the total electronic charge density distribution is demonstrated in this short perspective. This is framed in the perspective of the ground breaking early work of Bader and coworkers, along with mathematicians who captured the essential nature of a molecule in a suitably compact form in real space. We see that this simple form is the Poincaré–Hopf relation for molecules and clusters and the Euler–Hopf relation in solids. Thom's theory of elementary catastrophes combined with the Poincaré–Hopf relation provides the inspiration for the new quantum topology. An alternative use of the Poincaré–Hopf relation, molecular recognition, is discussed. Quantum topology is then used to create a topology phase diagram for both molecules and solids. The author adds their perspectives of the huge potential of the quantum topology approach by demonstrating the ease with which new theoretical ideas can be generated. © 2013 Wiley Periodicals, Inc.

Surprising Electronic Structure of the BeH– Dimer: a Full-Configuration-Interaction Study

The electronic structure of the beryllium hydride anion, BeH(-), was investigated at valence full-configuration-interaction (FCI) level, using large cc-pV6Z basis sets. It appears that there is a deep change of the wave function nature as a function of the internuclear distance: the ion structure goes from a weakly bonded Be···H(-) complex, at long distance, to a rather strongly bonded system (more than 2 eV) at short distance, having a (:Be-H)(-) Lewis structure. In this case, it is the beryllium atom that formally bears the negative charge, a surprising result in view of the fact that it is the hydrogen atom that has a larger electronegativity. Even more surprisingly, at very short distances the average position of the total electronic charge is close to the beryllium atom but on the opposite side with respect to the hydrogen position.

First-Principles Molecular Dynamics at a Constant Electrode Potential

A simulation scheme for performing first-principles molecular dynamics at a constant electrode potential is presented, opening the way for a more realistic modeling of voltage-driven devices. The system is allowed to exchange electrons with a reservoir at fixed potential, and dynamical equations for the total electronic charge are derived by using the potential energy of the extended system. In combination with a thermostat, this potentiostat scheme reproduces thermal fluctuations of the charge with the correct statistics, implying a realistic treatment of the potential as a control variable. Practically, the dynamics of the charge are decoupled from the electronic structure calculations, making the scheme easily implementable in existing first-principles molecular dynamics codes. Our approach is demonstrated on a test system by considering various test cases.

Spin-dependent Smoluchowski effect

Electron charge near atomically sharp corrugations at the surfaces of a solid tends to spill out and smoothen the abrupt variation of the positions of the positively charged atomic nuclei. The reason is that electrons are much less localized than nuclei. This has been discussed already some 70 years ago by Smoluchowski [R. Smoluchowski, Phys. Rev. 60, 661 (1941)], and the corresponding effect of charge redistribution near surface corrugations bears his name. The Smoluchowski effect focuses on the total electron charge density. It neglects that electrons---in addition to charge---also carry a spin. We discuss spin-dependent electron spill out and demonstrate in a combined theoretical and experimental work that compelling consequences for spin-polarization and spin-dependent transport arise at the edges of magnetic nanostructures due to the spin-dependent Smoluchowski effect. We find a variation of the tunnel magnetoresistance ratio of more than 20$%$ on a length scale of a few atomic diameters.

The elimination of interface charge density singularity in single layer organic semiconductor structures

The arguments are presented that the assumption of a zero electric field at the charge carrier injection electrode/organic interface, as assumed by the current-voltage model of shallow traps occupying a single energy level within the organic semiconductor charge transport band as well as by the model of traps exponentially distributed in energy, is invalid in principle. In consequence of this fact, it is shown that the value of material parameters is strongly related to the bias dependent non-zero electric field at the charge-injecting interface. A set of published room temperature current-voltage data of a single layer, electron-only, metal/organic semiconductor structure is used in order to show explicitly that the singularity of free (or total) electron charge carriers at the injecting interface and the associated space charge limited current characteristics reflects an unrealistic assumption of the above two models. For the model of traps exponentially distributed in energy, the charge traps density and the associated non-zero interfacial electric field are uniquely determined under a subsidiary condition of minimal energy of charges in an external electric field. The resulting (bias dependent) spatial distribution of the internal electric field and the spatial dependence of the electron density turns out to be practically uniform throughout the organic sample in agreement with the predictions of the model of shallow traps occupying a single energy level. The internal electric field and the charge density within the narrow midway region of the organic are, at each bias, invariant to the variation of the trap density and the associated interfacial electric field. It is also shown that the drift-diffusion electron transport interpreted in terms of the model of shallow traps occupying a single energy level is incompatible with the published measurements.

Direct laser acceleration of electron by an ultra intense and short-pulsed laser in under-dense plasma

Direct laser acceleration (DLA) of electron by an ultra intense and short-pulsed laser interacting with under-dense plasma is investigated based on 2.5-dimensional particle-in-cell simulation. A high-density electron beam is generated by the laser longitudinal ponderomotive force. Although the total number of DLA electrons is significantly smaller than the number of electrons trapped in the bubble, the total charge of high-energy DLA electrons (E>800MeV) reaches 67 pC/μm. It is found that the electron beam occurs in a two-stage acceleration, i.e., accelerated in vacuum by the laser directly soon after a DLA process in plasma. The beam is accelerated violently with effective acceleration gradient in 100 GeV/cm. The energy spectrum of electrons presents a Maxwellian distribution with the highest energy of about 3.1 GeV. The dependence of maximum electron energy and electric quantity with laser intensity, laser width, pulse duration, and initial plasma density are also studied.

Synthesis, spectroscopic characterization, calculational studies and in vitro antitumoral activity of 4-(3-(1H-imidazol-1-yl)propyl)-(thiophen-2-ylmethyl)-1H-1,2,4-triazol-5(4H)-one

4-(3-(1H-imidazol-1-yl)propyl)-(thiophen-2-ylmethyl)-1H-1,2,4-triazol-5(4H)-one (IPTT), C 13H 15N 5OS, was synthesized and characterized by 13C NMR, 1H NMR, IR and single-crystal X-ray diffraction. The structure of IPTT is stabilized by three intermolecular hydrogen bonds and by intermolecular C H⋯ π interaction. The compound IPTT was modelled by using DFT method. Calculations of vibrational frequencies, gauge including atomic orbital (GIAO), 1H and 13C NMR chemical shifts of IPTT in the ground state, total electronic charge density map and frontier molecular orbitals were performed at B3LYP/6-31 G(d) level of theory were carried out by using DFT method with 6-31 G(d) basis set. The structural parameters obtained by geometry optimization, the theoretical vibrational frequencies and chemical shift values are in good agreement with experimental ones. FT-IR, NMR and X-ray analytical results of IPTT show that the compound exists as keto form, that was supported by DFT calculations. In addition, in vitro studies showed hopeful antitumoral activity of the title IPTT compound.

First principles calculations of the relaxed structural and electronic properties of Cu nanobelts

Calculations have been performed for the relaxed structural and electronic properties of Cu nanobelts with the cross-section 3×5, 3×7, 3×9 and 3×11 atomic layers, using the first-principles projector-augmented wave (PAW) potential within the density functional theory (DFT) framework. For all four size Cu nanobelts, most atoms relax inward, and the farther an atom is from the center of the nanobelt, the larger is the amount of inward relaxation and the smaller the total electronic charge. Compared with the (001) plane of Cu bulk crystal, a metallic (delocalized) bonding character obviously appears along the surface atoms as well as along the surface atoms and their first nearest neighbor atoms. The decrease in the coordination number and thus the decrease in restrictions for atoms distant from the center of the nanobelt lead most electrons to range in the higher energy region of the occupancy state.

First-principle calculation of electrons charge density in the diamond–structure semiconductor crystals

A computational study of the total electrons charge density in the diamond-structure semiconductor crystals has been performed. In a typical modern electronic structure calculation, the charge density is obtained from a certain density functional, however, the charge density in this work was obtained from first principles. It is assumed that the one-electron Bloch functions for the crystals will not very seriously differ from the wave functions in the atomic systems, therefore, they are represented by the well known normalized Slater atomic orbital for multi-electron atoms and ions. Since the spherical harmonics are expressed in the spherical coordinate system, all the calculations are done in this system. The wave functions and the total electron charge densities are calculated along the [l00], [010], and [00l] directions for the state k=0. The atomic system of units is used throughout the calculations. i.e. distances are expresPsed in unit of the Bohr radius, and charges in unit of the electronic charge. It has been found that in each crystal, the total electrons charge density along the [100] and [010] directions are equal, however, the charge densities at a given distance from the center of the cell along [001] and [100] directions are not exactly equal; the density along [100] been always higher. This shows that the potentials arising from the electrons are not spherically symmetric. The results are presented and discussed

The drift-diffusion interpretation of the electron current within the organic semiconductor characterized by the bulk single energy trap level

The closed solution for the internal electric field and the total charge density derived in the drift-diffusion approximation for the model of a single layer organic semiconductor structure characterized by the bulk shallow single trap-charge energy level is presented. The solutions for two examples of electric field boundary conditions are tested on room temperature current density-voltage data of the electron conducting aluminum/tris(8-hydroxyquinoline aluminum/calcium structure [W. Brütting et al., Synth. Met. 122, 99 (2001)] for which jexp∝Va3.4, within the interval of bias 0.4 V≤Va≤7. In each case investigated the apparent electron mobility determined at given bias is distributed within a given, finite interval of values. The bias dependence of the logarithm of their lower limit, i.e., their minimum values, is found to be in each case, to a good approximation, proportional to the square root of the applied electric field. On account of the bias dependence as incorporated in the minimum value of the apparent electron mobility the spatial distribution of the organic bulk electric field as well as the total charge density turn out to be bias independent. The first case investigated is based on the boundary condition of zero electric field at the electron injection interface. It is shown that for minimum valued apparent mobilities, the strong but finite accumulation of electrons close to the anode is obtained, which characterize the inverted space charge limited current (SCLC) effect. The second example refers to the internal electric field allowing for self-adjustment of its boundary values. The total electron charge density is than found typically to be of U shape, which may, depending on the parameters, peak at both or at either Alq3 boundary. It is this example in which the proper SCLC effect is consequently predicted. In each of the above two cases, the calculations predict the minimum values of the electron apparent mobility, which substantially exceed the corresponding published measurements. For this reason the effect of the drift term alone is additionally investigated. On the basis of the published empirical electron mobilities and the diffusion term revoked, it is shown that the steady state electron current density within the Al/Alq3 (97 nm)/Ca single layer organic structure may well be pictured within the drift-only interpretation of the charge carriers within the Alq3 organic characterized by the single (shallow) trap energy level. In order to arrive at this result, it is necessary that the nonzero electric field, calculated to exist at the electron injecting Alq3/Ca boundary, is to be appropriately accounted for in the computation.

An insight into optical rotation of amino-acids

Optical specific rotation of naturally occurring L-amino-acids depend upon physico-chemical properties of amino-acids, solvent used for their preparation and incident radiation. The most important parameters like total polarization, dielectric constant, dipole moment, density and molecular weights of the amino-acids are connected to optical specific rotation by mathematical equations. The present paper elucidates the variation in specific optical rotation of amino-acids with a few physico-chemical properties namely total unbound electronic charge, molecular weight, furthest distance of substituent group from asymmetric carbon atom, surface area, charge density, molecular volume, solubility and pI values. Probable reasons for these observations have been offered. Intrinsic conformations of amino-acids and the total polarization with incident low ionizing radiation for amino-acids should lead to measurable changes in specific optical rotation as compared to un-irradiated amino-acids. So long the bonds between asymmetric carbon atom and functional groups do not disrupt upon impingement of low ionizing radiation the variation in optical rotation compared to un-irradiated amino-acid should be obtained. The potential uses of this study in dosimetry and radioprotection are bright.

Comparison of Bowing Behaviors Between III–V and II–VI Common-Cation Semiconductor Ternary Alloys

The scope of the present investigation is to make a clear contrast between the bandgap bowing characters of III–V and II–VI compound-semiconductor common-cation ternary alloys. For this aim, both the sp 3 s * tight-binding method, with the inclusion of spin–orbit coupling, and the full-potential linear augmented plane-wave technique are used to calculate the partial and total densities of states, the constituent ionicity, and the total electron charge density for the common-cation GaSb x As1−x and CdSe x Te1−x ternary alloys. The results show that the bowing is sensitive to competition between the anions for trapping/losing electric charges. The lack of this competition would result in complete absence of the bowing, as is the case for common-anion ternary alloys. In the common-cation ternary alloys studied herein, the bowing is found to be proportional to the electronegativity of the anions χ anion (i.e., the 6-valency anions are more electronegative than the 5-valency ones, and consequently the former result in stronger intercompetition and yield stronger bowing in the II–VI alloys) and also proportional to the relative mismatch in electronegativity between the competing anions \(({\Updelta}\chi^{\rm{anion}}/\chi^{\rm{anion}}_{\rm{ave}}).\) The excellent agreement between our theoretical results and recent photoluminescence data corroborates our claim.