Spatial Distribution Of Electron Density Research Articles

Spin-Orbit Coupling Calculation Combined with the Reference Interaction Site Model Self-Consistent Field Explicitly Including Constrained Spatial Electron Density Distribution.

Studying the radiative and non-radiative decay processes of molecules in a solution is an important issue in the design of organic and functional molecules. Theoretical approaches have great potential for revealing this decay process through computation of various parameters, such as the energy surfaces at the excited state and spin-orbit coupling (SOC). The development of quantum chemical programs has enabled the calculation of SOC values to become popular for the gas phase. However, SOC calculations in solution have some difficulties that need to be overcome. In the present study, the authors combined the SOC calculations with the reference interaction site model self-consistent field explicitly including constrained spatial electron density distribution. To validate the reliability of our method, the decay process of dimethylaminobenzonitrile in cyclohexane and acetonitrile was studied. By computing the SOC values in both solution systems, the authors were able to investigate the decay process at the atomistic level. Furthermore, a natural transition orbital analysis and the measurement of the decomposed SOC values were found to provide a clear understanding of intersystem crossing.

Dynamics of implosion phase of modified plasma focus studied via laser interferometry and electrical measurements

Dynamics of the implosion of the dense plasma focus play an essential role in converting electrical energy into the kinetic energy of the current sheath and subsequent production of accelerated electrons, ions, hard X-ray, and neutron emission. This paper presents the analysis of the implosion parameters, such as the implosion velocity and imploding mass, coupled with electrical parameters observed on the PF-1000 facility with a modified electrode system. The first two parameters are based on the 16-frame Mach–Zehnder interferometer, which provides the spatial distribution of electron density in a time sequence. Measurement of the total current, current derivative, and voltage enables us to evaluate the total inductance and kinetic energy driven by the capacitor bank. Then comparing the inductances and kinetic energies evaluated from the interferograms and electrical waveforms can provide more precise information on the current flowing in the imploding sheath. We present a possible way to deal with the fact that only part of the total current flows through the imploding layer. With the supposition that the rest of the current flows close to the insulator, we conclude that roughly 70% of the total current flows through the pinch, which is in good agreement with an input parameter of the Lee model, for example.

Multipolar Atom Types from Theory and Statistical Clustering (MATTS) Data Bank: Impact of Surrounding Atoms on Electron Density from Cluster Analysis.

The multipole model (MM) uses an aspherical approach to describe electron density and can be used to interpret data from X-ray diffraction in a more accurate manner than using the spherical approximation. The MATTS (multipolar atom types from theory and statistical clustering) data bank gathers MM parameters specific for atom types in proteins, nucleic acids, and organic molecules. However, it was not fully understood how the electron density of particular atoms responds to their surroundings and which factors describe the electron density in molecules within the MM. In this work, by applying clustering using descriptors available in the MATTS data bank, that is, topology and multipole parameters, we found the topology features with the biggest impact on the multipole parameters: the element of the central atom, the number of first neighbors, and planarity of the group. The similarities in the spatial distribution of electron density between and within atom type classes revealed distinct and unique atom types. The quality of existing types can be improved by adding better parametrization, definitions, and local coordinate systems. Future development of the MATTS data bank should lead to a wider range of atom types necessary to construct the electron density of any molecule.

Role of lone-pair electron localization in temperature-induced phase transitions in mimetite.

The crystal structure of mimetite Pb5(AsO4)3Cl, a phosphate with apatite structure-type has been investigated in situ at 123, 173, 273, 288, 353 and 393 K. A careful inspection of the diffraction pattern and subsequent structure refinements indicated that mimetite transforms from the monoclinic to the hexagonal polymorph with increasing temperature. At 123 K, a monoclinic superstructure, mimetite-2M, with cell parameters a = 20.4487 (9), b = 7.4362 (2), c = 20.4513 (9) Å, β = 119.953 (6)°, V = 2694.5 (2) Å3 and space group P21 was observed. From 173 to 353 K, the reflections of the supercell were evident only along one direction of the corresponding hexagonal apatite-cell and the structure transforms to the polymorph mimetite-M with space group P21/b and unit-cell parameters a = 10.2378 (3), b = 20.4573 (7), c = 7.4457 (2) Å, β = 120.039 (5)°, V = 1349.96 (9) Å3. Only at higher temperature, i.e. 393 K, does mimetite adopt the hexagonal space group P63/m characteristic of apatite structure-types. The role of the electron lone pairs of Pb atoms in the phase transition was investigated through the analysis of the electron localization function (ELF) calculated based on the DFT-geometry optimized structures of the three polymorphs. The changes in spatial distribution of the 6s2 electron density during the phase transitions were explored by means of the Wannier Function Centres (WFCs) derived from ab initio molecular dynamics trajectories. In the high-temperature hexagonal structure the 6s2 electrons are spherically symmetric relative to the position of Pb atoms. At low temperature the maximum of 6s2 electron density is displaced relative to the position of Pb atom contributing to the polar interaction in the monoclinic polymorphs.

Recent progress on the J-TEXT three-wave polarimeter-interferometer

The J-TEXT three-wave polarimeter-interferometer system (POLARIS), which measures time-space distribution of electron density and current density, has been optimized with both the optical system and the equilibrium reconstruction method. The phase resolution of a Faraday rotation angle has been improved from 0.1 to 0.06 degree in chords from –0.18 to 0.18 m (plasma minor radius), and the sawtooth oscillation behavior has been detected by Faraday rotation angle measurement. By combining the POLARIS measured data and the equilibrium and fitting code (EFIT), an upgraded equilibrium reconstruction method has been developed, which provides a more accurate temporal and spatial distribution of current density and electron density. By means of the optimized POLARIS and improved equilibrium reconstruction, variations of profiles with increasing density have been carried out, under both Ohmic and electron cyclotron resonance heating discharges.

Propagation characteristics of relativistic ultrashort laser pulse in inhomogeneous plasma

We study the propagation of a relativistic ultrashort laser pulse in two-dimensional inhomogeneous plasma with a density ripple based on the theoretical analysis and the particle-in-cell simulation. An analytical solution of the laser pulse propagating in the homogeneous plasma is completely obtained. It is found that the stable propagation of the relativistic ultrashort laser pulse in homogeneous plasma can be realized, and the propagation distance and intensity of the laser pulse and the spatial distribution of electron density can be effectively modulated by adjusting the pulsewidth of the incident laser and the plasma frequency. More interestingly, in the inhomogeneous plasma with a density ripple, when the wave amplitude of the density ripple is less than a critical value, the intensity of the ultrashort laser pulse is almost unchanged and the propagation characteristics of the laser in the inhomogeneous plasma are basically consistent with those in the homogeneous plasma. However, when the wave amplitude of the density ripple is larger than the critical value, the inhomogeneity of the plasma has an obvious effect on the laser characteristics, and the intensity and the spatial distribution of the laser pulse will be modulated by the plasma density ripple. The influence of the laser pulsewidth, plasma density, and plasma density ripple on the laser characteristics is discussed in detail.

Analytical model of a short DC glow discharge in the presence of significant radial ambipolar diffusion losses

We present a simple analytical model of a short direct-current glow discharge (without positive column) that is applicable for the case of narrow discharge tubes when radial losses of charged particles due to ambipolar diffusion significantly influence discharge properties. The model is based on the analytical parameterization of the non-local ionization produced by fast electrons, which allows obtaining an exact solution of the ambipolar diffusion equation with radial particle losses written in the τ-approximation. Analysis of the spatial distribution of electron density in the near-cathode plasma regions of a discharge allow obtaining an explicit expression for the position of electric field reversal in the negative glow that is independent of electron temperature and interelectrode distance. The latter fact makes the model viable for description of near-cathode plasma regions in the general case of a discharge with a positive column. The procedure for obtaining quantitative estimates and interpretation of experimental data on discharge properties using the proposed model is presented and discussed in detail.

Intercalation of Li Atoms in TaSe2 Film's Anode with LiClO4/PEO Polymer Electrolyte: First Principles Calculation

Using the methods of electron density functional and pseudopotential from the first principles, the total energy, energy reliefs and migration barriers of Li atoms in the interlayer space of layers of anode material made of 2H-TaSe2, 2H-TaSe2 with molecules of polymer electrolytes LiClO4, PEO and LiClO4/PEO, charges on Se atoms limit the interlayer space2H-TaSe2, spatial distributions of valence electron density and their cross sections.

Energy levels of acceptor impurities in β-Ga2O3 nanostructures

Applying the methods of the density functional theory and ab initio pseudopotential, the characteristics of the energy levels of acceptors in β-Ga2O3 nanostructures are obtained from the first principles. Mg and Ca are most favorably included in the position of Ga1 and Ga2 in both the cluster and the film. N is most favorably included in the O1 position in the film. The spatial distribution of valence electron density, the density of states, acceptor levels, and band gap width for these nanostructures are calculated.

Investigation of the metastable structures of polyiodide in acetonitrile studied using global reaction route mapping and the reference interaction site model self-consistent field explicitly including constrained spatial electron density distribution.

In this study, we theoretically analyzed the metastable structures of polyiodide (I7-) in the gas and acetonitrile phases using global reaction route mapping and the reference interaction site model self-consistent field explicitly including constrained spatial electron density distribution. From the chemical reaction pathways of I7- in acetonitrile, it was found that there would be 2 types of isomerization pathways. One proceeds with constant stoichiometry and the other takes place by breaking and forming I-I bonds. In addition, we discovered that I7- had various metastable structures within ∼10 kcal mol-1. Comparing the most stable structure in the gas and acetonitrile phases, the tetrapot type is found to be the most stable structure in the gas phase; however, it is the zigzag type in acetonitrile. In order to understand this difference, we performed the decomposition analysis of the thermal correlation term in the gas and acetonitrile phases. It was found that thermal correction plays a key role in the stability and we could explain the difference in the population of the EQ states of I7- in each phase. Overall, we revealed that the solvation effect must be one of the crucial factors to stabilize the isomers of I7- and determine the chemical reaction pathways.

Performance of GPS Positioning in the Presence of Irregularities in the Auroral and Polar Ionospheres during EISCAT UHF/ESR Measurements

Irregularities in the spatial distribution of ionospheric electron density introduce temporal fluctuations in the intensity and phase of radio signals received from Global Navigation Satellite Systems (GNSS). The impact of phase fluctuations originating from irregularities in the auroral and polar ionospheres on GPS positioning was investigated on three days in March 2018 in the presence of quiet-to-moderately disturbed magnetic conditions by combining measurements from GPS and EISCAT UHF/ESR incoherent scatter radars. Two different positioning solutions were analysed: broadcast kinematic (BK) and precise static (PS). The results show that the propagation through irregularities induced residual errors on the observables leading to an increase in the positioning error, in its variability, and in the occurrence of gaps. An important aspect emerging from this study is that the variability of the 3-D positioning error was reduced, and the presence of gaps disappeared when the positioning solutions were evaluated at a 1 s rate rather than at a 30 s rate. This is due to the transient nature of residual errors that are more significant over 30 s time intervals in the presence of irregularities with scale size between few kilometres in the E region to few tens of kilometres in the F region.

Analytical second derivatives of the free energy in solution by the reference interaction site model self-consistent field explicitly including constrained spatial electron density distribution

The application of analytical derivative methods to solution systems is important because several chemical reactions occur in solution. The reference interaction site model (RISM) is one of the solvation theories used to study solution systems and has shown good performance, especially in the polar solvent systems. Although the analytical first derivative based on the RISM coupled with quantum methods (RISM-SCF) has already been derived, the analytical second derivative has not been proposed yet. Therefore, in this study, the analytical second derivative was derived using RISM-SCF explicitly including constrained spatial electron density distribution (RISM-SCF-cSED). The performance of this method was validated with the Hessian calculations of formaldehyde and para-nitroaniline in solution, and the results demonstrated that the method accurately calculated frequency values at a small computational cost.

Accurate Absorption Energy Calculations in Solution Using the Reference Interaction Site Model Self-Consistent Field Including the Constrained Spatial Electron Density Distribution

The solvation effect is an important factor determining the properties of molecules in solution. The reference interaction site model (RISM) is a powerful method to treat the solvation effect with pair-correlation functions, such as a radial distribution function. This study developed a hybrid method between quantum mechanics and RISM using the spatial electron density distributions on each atomic site (RISM-SCF-cSED). Sophisticated quantum mechanical approaches can be used to consider the solvation effect because the computational cost of RISM-SCF-cSED is reasonable. In this study, the absorption energies of 5-(dimethylamino)-2,4-pentadienal in various solutions were calculated using RISM-SCF-cSED. The experimental data were well reproduced with an average errors of ∼0.06 eV, using multi-reference perturbation theory.

Active Control of Electromagnetic Attenuation Characteristics of Planar Inductively Coupled Plasma

In this article, an inductively coupled plasma (ICP) source with planar transparent cavity is designed, and the active control of ICP on the attenuation effect of electromagnetic wave is studied. The scattering parameters calculation model of ICP is established based on the COMSOL fluid model combined with Z transform finite-difference time domain (ZT-FDTD) method. A point wave source composed of continuous reflection waves in the plasma is observed through the numerical simulation of the model, and the location of the wave source depends on the spatial distribution of the peak electron density. The effects of different pressure (10 mtorr–1 torr), working gas (Ar and O2), and power (200–600 W) on the electromagnetic scattering characteristics are compared through numerical calculation and experimental measurement. The results show that the attenuation frequency band and amplitude can be actively controlled by changing external factors of ICP, such as gas pressure, working medium gas, and power. With the increase of power, the attenuation peak moves to the high-frequency band. With the increase of pressure, the fluctuation of attenuation curve is enhanced, and the attenuation bandwidth is increased. The O2-ICP is more capable of absorbing wave power of the low band below 6 GHz, while the Ar-ICP is more effective in 6–14 GHz. The research results broaden the active stealth mode of aircraft in complex electromagnetic environment.

Determination of electron properties of a helium atmospheric pressure plasma jet with a grounded metallic target

AbstractAn atmospheric pressure plasma jet (APPJ) was configured to generate helium atmospheric pressure plasma. A kilohertz AC voltage was applied to APPJ electrodes, and a grounded aluminum target was placed outside of a quartz tube on the plasma propagation axis. The electron temperature and density of APPJ were determined using the emissivity of continuum radiation in 380–500 nm spectra. Electron temperatures and densities for the helium plasmas with and without a target were compared. When the target was installed, the continuum radiation was enhanced, and electron density increased. Spatial distributions of electron temperature and density from the nozzle of the quartz tube to the target were examined. The electron temperature increased up to ∼2.75 eV, and electron density increased and decreased along APPJ propagation.

Finite Element Based Comparative Analysis of Positive Streamers in Multi Dispersed Nanoparticle Based Transformer Oil

The dispersion of dissimilar nanoparticles (NPs) in transformer oil (TO) has a major impact on fast propagating positive streamers. This work investigates the positive streamer dynamics in TO modified by dispersing both Fe3O4 and Al2O3 NPs at a homogenous concentration. The hydrodynamic drift diffusion model of positive streamer evolution and propagation are solved using the commercial software package COMSOL Multiphysics. The impact of multiple NPs (MNPs) has been analysed for streamer propagation, electric field intensity, electron density, and space charge density of modified TO. MNPs successfully reduce streamer propagation velocity by 50%, 17%, and 37.5% comparing to pure oil, Fe3O4 based nanodielectric fluids (NDFs), and Al2O3 based NDFs, respectively. The spatial distribution of electron density reveals the loss of electrons from the ionization region until the saturation of NPs. A comparative study demonstrates that MNPs significantly alter the streamer dynamics and augment the dielectric strength of TO compared to individual NPs.

In suit monitoring of solidification mode, porosity and clad height during laser metal deposition of AISI 316 stainless steel

The solidification mode, random pore defects and deposition height were monitored during the laser metal deposition process by using a laser-induced plasma signal. The spectral lines of six elements that determine the solidification mode of austenite steel were extracted and set as features of the dataset. Two different solidification modes were successfully predicted through a support vector machine model. Random pore positions inside the deposition layer were identified by monitoring the statistical parameters of the plasma spectrum. Relationships between the pore position and the statistics features of the spectrum signal were developed. The spatial distributions of plasma temperature, electron density and signal intensity were characterized, and their connection with the deposition height was studied. The electron density and signal mean intensity were found to have linear relationships with the deposition height and can be used to detect abnormal height changes during the manufacturing process.

Spatial distribution of atomic electronic density for elements 1–54 as coming from a Hartree–Fock treatment within the minimum atomic parameters paradigm

AbstractThe minimum atomic parameters/Moscow–Aachen–Paris (MAP) basis sets—reintroduced in the previous paper—are analyzed with respect to spatial features as orbital shape, possible fits to alternative orbital sets (numerical or quasi‐numerical orbitals, nodeless Slater orbitals), respect of Kato's condition and radial distribution of energy components. For comparing orbital spaces the Frobenius angle between the orbital subspaces they span is introduced as numerical tool. It is shown that the electronic density of the MAP states is depleted around the nucleus with respect to the other orbital sets. Despite this, the similarity between the respective subspaces in all cases (except a unique case of the Pd atom) as measured by the cosine of the Frobenius angle amounts above 0.96 for all atoms. Deviations from the perfect value of Kato's condition amounts systematically to 0.3 and 0.5 for all elements considered. Integrating one‐electron energy contributions from r = ∞ to a finite radius, MAP and Bunge orbitals show about the same values, but for the inner region governed by the polynomial oscillations.

The Vertical Extent of Enhanced Densities in Cusp‐Like Regions of the Ionosphere of Mars

AbstractUnusually large values of peak electron density in the ionosphere of Mars are occasionally observed in cusp‐like regions of crustal magnetic field. These features are observed as atypical examples of oblique echoes in ionograms. However, the vertical extent over which electron density values are enhanced has not yet been determined. Furthermore, the physical processes responsible for these striking features are not yet understood. Here we analyze ionograms from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on Mars Express to better constrain the spatial distribution of electron density in and around these rare ionospheric features. Data from orbits 2359, 2491, 4469, and 4513 are examined. When peak electron density is unusually large, electron density values from the peak to 165 km are increased by 30% ± 10% and the electron density at the spacecraft (∼300–400 km) is diminished. We investigate whether the central portion of an oblique echo is equivalent to a nadir echo, which would permit the reliable determination of an electron density profile in instances of unusually large peak electron densities. We find that uncertainties in the location of the center of an oblique echo render this approach unfeasible. We also report that 86.5 μs should be subtracted from travel time values reported in current MARSIS data products released prior to 2019.

Temporal-spatial dynamics of electronic plasma in femtosecond laser induced damage.

In this study, transient temporal-spatial evolutions of femtosecond (fs) laser pulse-induced filaments and electronic plasma when laser induced damage occurred in fused silica were investigated using fs time-resolved pump-probe shadowgraphy. The transient peak electron density increased and then decreased as delay time of probe beam increased. Its corresponding spatial positions moved from the sample surface to the inside of the sample, but remained at the nonlinear focus for a relatively long time. The maximum electron density increased as pump energies increased and then became saturated at 8 μJ, above which laser-induced material damage occurred. The material damage threshold electron density was approximately 1.27×1020 cm-3. The laser-induced material damage position corresponded to the position of the maximum electron density. Furthermore, the material damage was extended from the nonlinear focus to the deeper parts of the sample at pump energies above 8 μJ. This tendency agreed well with the spatial distribution of the maximum transient electron density at each propagation depth, implying that the fs time-resolved pump-probe shawdowgraphy is a meaningful tool for predicting the distribution of laser-induced microstructures in ultrafast laser micromachining.