Charge Density Distribution Research Articles

Synthetic, Electrochemical, DFT, and Synchrotron X-ray Charge-Density Studies on Oxo-centered Triruthenium Clusters Supported by Electron-Withdrawing Carboxylates.

We herein report the synthesis, characterizations, and synchrotron X-ray charge-density studies of oxo-centered triruthenium(II,III,III) clusters [Ru3O(CHCl2COO)6(py)3] (1) and [Ru3O(CHCl2COO)6(CO)(py)2] (2) (py = pyridine). Dichloroacetate was chosen for its large scattering factor of the Cl atom, and its electron-withdrawing nature results in significant stabilization of the targeted lower-valent Ru3II,III,III state in the cluster framework. Multipole analysis revealed that the difference in electron populations between two crystallographically independent Ru centers is small for 1 (Δ = 0.30 e) but large for 2 (Δ = 1.46 e). Remarkable differences between 1 and 2 are also found in their static deformation density maps; substantial local charge depletion was found around the central μ3O atom for 1, which is less pronounced for 2. According to the topological characterization of Ru-μ3O bonds associated with the bond critical point, bcp, the electron density, ρbcp, is in the range of 0.79-0.89 e Å-3, and the total energy density, Hbcp, is in the range of -0.21 to -0.05 hartree Å-3. These findings represent the first charge-density distribution analysis of mixed-valence multinuclear Ru complexes including comparison between 3d and 4d transition-metal systems.

Finite Element Analysis of Electrostatic Coupling in LISA Pathfinder Inertial Sensors

In the LISA Pathfinder (LPF) mission, electrostatic noise can reach the femto-Newtonian level despite the fact that the LPF’s sensors are equipped with potential shielding. Most of the existing simulation studies focus on the electrostatic edge effect and related fields, while the simulation study of the patch effect is neglected. For that reason, this paper analyzes the basic principle of electrostatic noise and constructs a simulation model for studying the coupling effects of a TM’s residual charge and stray bias voltage. The patch effect and other perturbation factors are simulated by the simulation model with finite element operation, focusing on the suppression effect of the protective ring on the edge effect, the realization of the patch effect in the simulation model, and the possible influence. The results show that electrode area and the spacing between the electrode and the TM together limit the suppression effect of the protective ring on the edge effect. The spatial and temporal variations of the patch effect significantly affect the distributed electric field between the electrodes and the TM, as well as the charge distribution density of the TM. In the worst-case scenario of LPF electrostatic input parameters, the electrostatic noise is about 1.03 × 10−15 m/s2/√Hz at 1 mHz, which is about 6% different from the expected performance estimate. Finally, considering the limitations of multiple environmental factors on the inertial sensors, the present model will be useful to explore the interactive effects of multi-field coupling and to further investigate the impact of low-energy electron charging on the performance of the inertial sensors.

Engineering of charge density at the anode/electrolyte interface for long-life Zn anode in aqueous zinc ion battery.

The aqueous zinc ion battery emerges as the promising candidate applied in large-scale energy storage system. However, Zn anode suffers from the issues including Zn dendrite, Hydrogen evolution reaction and corrosion. These challenges are primarily derived from the instability of anode/electrolyte interface, which is associated with the interfacial charge density distribution. In this context, the recent advancements concentrating on the strategies and mechanism to regulate charge density at the Zn anode/electrolyte interface are summarized. Different characterization techniques for charge density distribution have been analysed, which can be applied to assess the interfacial zinc ion transport. Additionally, the charge density regulations at the Zn anode/electrolyte interface are discussed, elucidating their roles in modulating electrostatic interactions, electric field, structure of solvated zinc ion and electric double layer, respectively. Finally, the perspectives and challenges on the further research are provided to establish the stable anode/electrolyte interface by focusing on charge density modifications, which is expected to facilitate the development of aqueous zinc ion battery.

Influence of the edge effect of the solenoid magnetic field on the discharge process of magnetron sputtering in long and narrow chambers

The fourth-generation light source or future particle accelerators have compact vacuum systems, resulting in a small flow conductance of the beam chamber. The development of NEG (Non-Evaporable Getters) films technology with distributed pumping is a good solution. This technology can obtain a pressure distribution with a small pressure gradient and an ultra-high vacuum of 10-8 Pa inside the vacuum chambers. In the magnetron sputtering process for NEG coating, the inhomogeneity of the magnetic field at the edge of the solenoid is a key parameter for affecting the stability of the magnetron sputtering discharge process. The influence mechanism of the edge magnetic field on the plasma discharge process and discharge uniformity was studied to optimize the coating parameters, which is very important. The Particle-In-Cell/Monte Carlo Collision (PIC/MCC) method was employed to simulate plasma discharge in a narrow vacuum chamber under various edge magnetic field conditions. The potential distribution, charged particle density distribution, and particle density distribution on the target were acquired for four sets of discharge parameters, followed by data processing and analysis. The electric field distribution during the discharge process is closely linked to the non-uniformity of the magnetic field at the solenoid's edge. The smaller Br (the radial component of the magnetic field) component of the magnetic field, the more uniform distribution of Ar+ on the target surface, and the smaller the difference along the length of the vacuum chamber. A smaller radial component (Br) of the magnetic field results in a more uniform distribution of Ar+ on the target surface and reduces variations in film thickness along the length of the vacuum chamber. This is attributed to the small distance between the inner wall of the vacuum chamber and the cathode target. The change in the edge magnetic field will result in the rapid migration of electrons to the inner wall of the vacuum chamber and insufficient collision with the discharge gas, making it challenging to sustain the discharge process. Moreover, fluctuations in the edge magnetic field of the solenoid induce gradient drift and curvature drift in charged particles, resulting in rapid electron loss and alterations in the density and potential distribution of charged particles at the ends of the vacuum chamber, ultimately leading to discharge instability. The research results show the importance of the edge magnetic field effect on the magnetron sputtering coating of the slender vacuum chambers, which provides an important reference for the segmented coating process of similar vacuum chambers in future accelerators.

Machine learning assisted mechanism modeling for gas phase electrohydrodynamic system

In this paper, a hybrid physics-data driven model for electrohydrodynamic gas system (EHDGS) was developed by combining artificial neural network (ANN) with mechanism modeling method. ANN was used to correlate the relationship between the variables (electrode distance, diameter of grounding cylinder, applied voltage, electric field gradient, etc.) in a needle-cylinder EHDGS and the initial space charge density. The results showed that the ANN model of nine neurons can well predict the initial space charge density. The coefficient of determination (R2) reaches 0.9874, and the mean absolute error is as low as 0.0067. Subsequently, a hybrid mechanism model where the initial space charge density was predicted from the ANN model was constructed to simulate the needle-cylinder EHDGS. The experiment with the needle-cylinder EHDGS was carried out. The simulation results were in good agreement with the experimental data, demonstrating the reliability of the proposed hybrid model. The electric field distribution, space charge distribution, and flow field distribution behavior of the EHDGS were then analyzed in detail. The effects of key parameters on the flow characteristics of EHDGS were systematically studied, showing that higher voltage and shorter distance give higher flow rate up to 2.5 m/s. The diameter of the cylinder also significantly influences the breakdown voltage. Three dimensionless groups were defined and their effects on spatial charge density distribution were investigated. This study provides both insights and an efficient tool for the design and optimization of EHDGS.

Unraveling the Role of Intrinsic Carbon Defects for the Heterogeneous Reduction of NO with NH3

ABSTRACT This study investigates the impact of intrinsic carbon defects on the reduction of nitrogen oxides (NOx) during coal combustion, with a focus on the synergistic effect of ammonia (NH3) and pulverized coal. Two representative computational models containing intrinsic carbon defects are described, and their influence on NH3 reduction of NO is studied. Stable species and transition states present in the pathways are calculated using B3LYP/6-31 G(d). Results indicate that exposed edge carbon atoms exhibit higher charge density distribution, affecting NH3 adsorption and NO reduction. The maximum energy barriers for both pathways do not exceed 45 kcal/mol, achievable in practical coal combustion systems. This paper also calculates the heterogeneous reduction process of a model without intrinsic carbon defects (Char model), with the aim of observing the specific effects of intrinsic carbon defects on the processes of migration of H/O atoms, migration and recombination of N atoms, and formation and desorption of N2 molecules. Furthermore, the analyses demonstrated an increase in the rate of heterogeneous reduction of NH3 and NO on defective carbon surfaces in comparison to the Char/NH/NO system, indicating that the intrinsic defects of the carbon have a contributory effect on the catalytic activity. With regard to the magnitude of the increase in reaction rate with increasing temperature, the presence of intrinsic defects in the carbon base serves to reinforce the role of temperature in the rate-determining step. Overall, this study provides insights into the role of intrinsic defects in carbon-based catalysis and offers implications for nitrogen oxide emission control strategies.

Insights into Ag2Mo3SeO12 for photovoltaic and optoelectronic applications: A theoretical exploration of its structural, electronic, and thermoelectric behavior

The theoretical investigation of the newly discovered quadruple perovskite Ag₂Mo₃SeO₁₂ was conducted using density functional theory (DFT) with the generalized gradient approximation (GGA-PBE) for the structural properties. This study examined the compound's structural, electronic, optical, and thermoelectric properties, utilizing the Tran Blaha modified Becke-Johnson exchange potential (mBJ) for accurate band gap measurement to overcome the bandgap underestimation by GGA-PBE. The stable structure was confirmed through energy-volume optimization and fitted with the Birch-Murnaghan equation of state, using PBE-GGA exchange correlation functional. The findings revealed a band structure with direct transition under the TB-mBJ approach with an energy gap of 1.45 eV. Detailed analyses were conducted, including the density of states and charge density distribution maps. Various optical parameters such as the dielectric function, absorption coefficient, refractive index, and reflectivity were computed, with the static dielectric constant measured at 6.3. Notably, a significant evolution of the absorption coefficient in the visible region highlights the potential of Ag₂Mo₃SeO₁₂ for solar cell and optoelectronic applications. These results pave the way for new photovoltaic material designs. Furthermore, the material demonstrates promising thermoelectric properties with an appropriate figure of merit, Seebeck coefficient, and electrical and thermal conductivity evolution under different temperature conditions, indicating its potential for photovoltaic and optoelectronic applications.

Enhanced magnetic refrigeration capacities of Er6FeSb2 by manganese substitution

Er6FeSb2 is a potential magnetic refrigeration material that can work at the liquid hydrogen temperature range. This work enhances the magnetic refrigeration performance of Er6Fe1-xMnxSb2 by Mn substitution. Mn doping increases the cell volume while maintaining the compound’s crystal structure type. It also results in an increase in the charge density distribution between Er1 and Fe/Mn. As the Mn content increases, the ferromagnetic exchange is enhanced, and the TC continuously increases. The Mn doping induces spin reorientation at low temperature, transforming compounds from traditional magnetocaloric effects to table-like magnetocaloric effects, greatly enlarge the cooling temperature range. When the content of Mn increases from x = 0 to x = 0.3, the δTFWHM increases from 26 K to 62 K, the −(ΔSM)max decreases from 12.1 J/(kg·K) to 5.9 J/(kg·K), and the RCP first increases and then decreases, reaching the maximum value of 435.0 J/kg at x = 0.2. This study opens a new path for the search of magnetic refrigeration material with large cooling temperature range.

First-principle study of the ground-state crystal structure and optoelectronic response of CsPbX3 (X= Cl, Br, I) for photovoltaic applications

The optoelectronic response and ground state crystal structure of tetragonal (P4/mbm), orthorhombic (Pmnb) and monoclinic (P21/m) phases of CsPbX3 (X = Cl, Br, I) are studied for optoelectronic applications using first principle simulations. Electric field gradient (EFG) and magnetic hyperfine interactions are investigated to explore the charge distributions surrounding the nucleus and local magnetic environment of the atomic nucleus. The orthorhombic phase of these compounds is more stable having lowest ground-state energy compared to tetragonal and monoclinic phases. The understudied halide perovskites have direct band gap nature and spin orbit coupling (SOC) effect splits Pb-p and X-p orbitals at the edges of conduction and valence band (CB and VB) respectively. At the edge of VB, the strongly hybridized X-p and Pb-p orbital and direct band gap nature of CsPbX3 is excellent for the light absorption and photovoltaic (PV) applications. The n-i-p configuration (FTO/ETL/CsPbX3/HTL/Au) of the simulated structure shows that CsPbI3 has improved power conversion efficiency (PCE) of 22.48 % and 22.32 % and quantum efficiency (QE) about ∼80 % in tetragonal and monoclinic phases respectively. The Pb and Cs values of EFG tensor in z-direction (Vzz) are close to each other, which show that the distribution of electronic charge density is similar near these nuclei. Moreover, Cs-s orbital has negligible contribution and Pb-p and I-p orbitals have higher contribution in the hyperfine field (HFF). The negative HFF indicates the opposite HFF contribution.

Deciphering the molecular complexity: Employing density functional theory to probe 2-aminopyridinium 4-methyl benzene sulfonate elucidates synthesis methodologies, spectroscopic trends, reactivity patterns, molecular dynamics, and antibacterial properties

Harnessing computational modeling with density functional theory (DFT) and the B3LYP functional, delved into molecular geometry, harmonic spectra, and vibrational spectra for 2-aminopyridinium 4-methylbenzene sulfonate (2AP4MBS). Leveraging VEDA software to conduct a detailed investigation into oscillation spectra, particularly focusing on both quantitative and qualitative facets of infrared (IR) and Raman spectra. Our work also explored natural bonding orbitals, Fukui analysis, RDG analysis, and net Mulliken charge calculations, hinting at potential charge transfer within the molecule. Experimental validation of UV–Vis spectroscopic analyses was conducted. Electron density homology surface mapping via electrostatic potential interface (ESP) revealed insights into size, shape, charge density distribution, and reactivity sites. Topological features were elucidated through ELF and LOL maps.Docking simulations shed light on binding energy and interactions with peptide molecules, offering potential pharmaceutical applications following Lipinski criteria and ADMET framework assessments.

Study on the Structure, Morphology, Dielectric, and Piezoelectric Properties of Large-Grain (Ba0.85Sr0.15)1-x Pb x TiO3 Ceramic System for 0.02 ≤ x ≤ 0.08.

Barium strontium lead titanate ((Ba0.85Sr0.15)1-x Pb x TiO3), along with various compositions (x(mol %) = 0, 2, 4, and 8), was synthesized through the conventional sol-gel reaction method. Following this, the resultant powders underwent a carefully controlled calcination process at 1000 °C for a period of 4 h. The examination of the crystalline phase of the calcined ceramics was conducted at room temperature using X-ray diffraction. Rietveld refinement of the XRD data, performed using FullProf, revealed that the samples exhibited a tetragonal structure within the space group P4mm. The impact of Pb doping on the lattice structure of BaSr1-x TiO3 was explored by analyzing the charge density distribution. The FTIR analysis unveiled a distinct absorptive band within the 450-600 cm-1 range, indicative of the stretching and bending vibrations associated with TiO6 octahedra. Notably, sintering the material at 1150 °C for 4 h resulted in improved densification, as observed in scanning electron microscopy images showcasing a nearly uniform distribution of densely packed grains. Through the utilization of Williamson-Hall plots derived from XRD data, the average particle diameter was estimated to fall within the range of 131.87-141 nm, with an associated uncertainty ranging from 5 to 10%. Additionally, the dielectric characteristics unveiled the presence of a negative dielectric constant (εr) spanning the frequency range from 1 kHz to 2 MHz. The (Ba0.85Sr0.15)1-x Pb x TiO3 ceramic displayed a widespread occurrence of negative permittivity, emphasizing the influence of dielectric resonance. The investigation revealed that the sintered ceramic with the formula (Ba0.85Sr0.15)1-x Pb x TiO3 exhibited exceptional piezoelectric properties, achieving the highest piezoelectric constant (d33 = 137 pC/N) and electromechanical coupling factor (k p = 0.49).

Investigating electrocatalytic properties of β12-borophene as a cathode material for an efficient lithium-oxygen battery: a first-principles study

Responding to the pressing need to mitigate climate change effects due to fossil fuel consumption, there is a collective push to transition towards renewable and clean energy sources. However, the effectiveness of this move depends on an efficient energy storage system that surpasses current lithium-ion battery technology. The lithium-oxygen battery, having significantly high theoretical specific capacity compared to other systems, has emerged as a promising solution. However, the issues of poor cathode electrode conductivity and slow kinetics during discharge product formation have limited its practical applications. In this work, the first principles-based density functional theory was used to investigate the electrocatalytic properties of β12-borophene as a cathode electrode material for a high-performance lithium-oxygen battery. The adsorption energy, charge density distributions, Gibbs free energy changes, and diffusion energy barriers of lithium superoxide (LiO2) on β12-borophene were calculated. Our findings revealed several important insights: The adsorption energy was found to be − 3.70 eV, suggesting a strong tendency for the LiO2 to remain anchored to the material during the discharging process. The dynamics in the charge density distributions between LiO2 and the β12-borophene substrate exhibited complex behavior. The analysis of the Gibbs free energy changes of the reactions yielded an overpotential of − 1.87 V, this moderate value suggests spontaneous reactions during the formation of the discharge products. Most interestingly, the density of states and band structure analysis suggested the preservation of metallic properties and improved electrical conductivity of the material after the adsorption of LiO2. Additionally, β12-borophene has a relatively low diffusion energy barrier of 1.08 eV, implying effortless diffusion of the LiO2 and an increase in the rate of discharging process. Ultimately, the predicted electronic properties of β12-borophene, make it a strong candidate as a cathode electrode material for an efficient lithium-oxygen battery.

First-principles studies on the oxygen vacancy formation in α-Na2FePO4F and β-Na2FePO4F

The orthorhombic β-Na2FePO4F has been extensively studied, however, a novel monoclinic α-Na2FePO4F has not been explored sufficiently. Oxygen vacancies (VO) can affect the physical and chemical properties of materials, and oxygen vacancy formation energy reflects the difficulty of VO formation. Using first-principles methods, we have calculated the formation energies of VO and their relevant charge states in both α-Na2FePO4F and β-Na2FePO4F. Our results reveal that charged vacancies (VO+1 or VO+2) are easier to form than neutral vacancies (VO0). The reduction of the Fermi level, the decrease in the oxygen partial pressure, or the increase of the temperature are found to decrease the formation energy of VO. The formation energy of VO in α-Na2FePO4F is slightly lower than that in β-Na2FePO4F. The electronic density of states of α-Na2FePO4F and β-Na2FePO4F suggest that more defect states are introduced into the band gap as the charge states increase. These defect states are mainly the 3d orbitals of the Fe atoms. The introduction of oxygen vacancies distorts the [FeO4F2] octahedra, which affect the charge density distribution and the defect states introduced in the band gap. Significantly, oxygen vacancies have a local impact on the charge density redistribution in both α-Na2FePO4F and β-Na2FePO4F. These findings provide theoretical insights into the formation of oxygen vacancies and the control of oxygen release.

Deep trapped bipolar heterocharges enable electret nanofibrous membranes for high-efficiency PM0.3 filtration

Recently frequent global pandemic outbreak triggers the demand of high-efficiency aerosol filtration materials. Most of traditional electret air filters can hardly achieve high efficiency (>99.99 %) due to limited charge density and inappropriate charge distribution. The influence mechanism of nanofibers bipolar heterocharge configuration on electrostatic capture of airborne particles is still confusing. Herein, a novel strategy to create high-efficiency air filters based on electret nanofibrous membranes with deep trapped heterocharge is reported. Space charges and dipole charges with opposite polarity are formed in electrospun membranes composed of different polymers under in-situ charge injection and electric poling during electrospinning. Nanoscale spatial surface potential mapping on individual nanofiber characterized by Kelvin probe force microscopy demonstrates bipolar heterocharge distribution. Numerical simulation shows that fiber heterocharge distribution endows the electret membrane with greater electrostatic field intensity gradient, resulting in stronger electrostatic force between nanofibers and airborne particles. With bipolar heterocharge configuration and bimodal fiber diameter distribution, the nanofibrous membranes exhibit high-efficiency low-resistance filtration property against 0.3 μm NaCl particles (99.994 %, 97.4 Pa) at 5.3 cm s−1. Furthermore, benefiting from charges with deep trap energy of 1.12 eV, the membranes still maintain 99.972 % filtration efficiency after 40 h exposure in 95 % relatively humidity. The prepared membranes brings new insight in the design of high-efficiency and long-term stability air filtration materials for public health precaution. This study not only reveals influence mechanism of nanofibers heterocharge distribution on electrostatic attraction, but also provides useful guidance for fiber charge configuration design to improve aerosol filtration performance of electret filters.

Joule heating for structure reconstruction of hard carbon with superior sodium ion storage performance

Hard carbon anode for sodium ion batteries still remains many challenges including insufficient cycling life and initial Coulombic efficiency (ICE), weak rate capability and poor compatibility in common ester electrolytes. Here, we propose a Joule heating post-treatment including multifield sintering method to reconstruct the structure of hard carbon from thick graphene layers to more disordered vortex layer structure composed of thin and curved graphite-like domains. The molecular dynamics simulation and differential charge density distribution demonstrate the crucial effect of electric field in strengthening the interaction between the polar molecule groups and the graphene layer, leading to the distortion and expanding of graphene layer. This is a universal and highly efficient strategy to modify various hard carbons within minutes. The optimized hard carbon anode exhibits exceptional rate capability and cycling stability with a high retention rate of 88.4% after 15,000 cycles at 10C in ether electrolyte. It also displays remarkably improved reversible capacity, initial Coulombic efficiency ICE of 89.5% and cycling stability in ester electrolyte. It is revealed by in-situ electrochemical impedance spectroscopy and atomic force microscopy that the spontaneous formation of a thin, stable and inorganic substance-rich solid electrolyte interface layer with significantly improved mechanical property is largely responsible for the outstanding sodium-ion transport kinetics and long lifespan.

Investigation of an absorption plasmonic electro-optical modulator based on the free carrier dispersion effect in the aluminum doped zinc oxide layer

A plasmonic electro-optical modulator, which is based on the free carrier dispersion effect, has been introduced here. The structure of the proposed modulator is a substrate of fused silica/gold/aluminum doped zinc oxide/hafnium dioxide/gold/air. The free carrier dispersion effect occurs in the aluminum doped zinc oxide (AZO) layer. As the electrical permittivity of the AZO layer is near zero (the epsilon near zero effect) at a wavelength of 1.55 μm, the amplitude of an electrical field is high in this layer, therefore, the modulator is highly sensitive to the varying refractive index of this layer. By applying a voltage to two gold layers, the electrical charge density changes in the AZO layer. Therefore, the real and imaginary parts of the refractive index have been changed, which led to a change in the absorption of the modulator. In order to obtain the charge density distribution in the AZO layer, the Poisson equation is solved by using the finite difference method. To investigate modulator absorption, the Nelder-Mead method is implemented in order to solve the dispersion equation numerically. Finally, the magnetic field, the electric field, and the time average of the Poynting vector have been given by using the least squares approximation method.

Conformational and Electron Density Analysis of Bicyclo[3.1.0] hexanes: All Roads Lead to Boats

In view of the existence of an optimal conformation for molecular recognition and bearing in mind that nucleosides exhibit a broad range of pharmaceutical properties, whereby their conformation has a key role in molecular recognition, the tendency of the pseudosugar moiety in carbanucleosides to adopt a boat‐like conformation has been studied on the basis of a bicyclo[3.1.0]hexane system, resulting in versatile druglike scaffolds to increase molecular recognition. It is already known that using this system as a pseudosugar can fix the conformation in the northern or southern geometry required for biological activity, according to the relative position of the three‐membered ring. By mapping their energy potential surface, we investigated the preference for boat‐like conformers in bicyclo[3.1.0]hexanes. DFT was utilized alongside NBO analysis to explore the enhanced stability of boat‐like conformers, also considering the influence of oxygen, sulfur, and selenium heteroatoms. Additionally, charge density distribution analysis using QTAIM identified key atoms contributing to stability changes. These findings will help to comprehend this behavior in the drug discovery process when conformationally restricted nucleosides are involved.

Global prediction of nuclear charge density distributions using a deep neural network

Global prediction of nuclear charge density distributions using a deep neural network

Fundamental difference between the mechanisms of electrostatic field screening in dense and thoroughly collisionless plasmas

When an external electric field appears in a homogeneous plasma, ions move into regions where their electrostatic energy is lower. Simultaneously, forces arise that counteract this effect, causing the plasma to reach equilibrium when the field disappears completely. In collisional plasma, the resulting charge inhomogeneities decrease both Coulomb energy and entropy. Randomly induced diffusion flows tend to hinder their growth, minimizing free energy at any point. Accordingly, in the Debye–Hückel theory, the external field strength decreases exponentially with distance within the plasma. In a collisionless plasma, an antiscreening mechanism operates differently. Each ion moves in a self-consistent field along distinct trajectories, following classical dynamics laws. An external field bends these trajectories, bringing ions into regions where their Coulomb energy is lower. The antiscreening mechanism occurs when ions accelerate into potential wells, increasing the distances between them along their trajectories and decreasing their number densities along these paths. The law of energy conservation for any single ion governs this principally nonlocal process, and the dependence of field strength on distance is not necessarily exponential. This paper demonstrates that the Debye–Hückel theory should not be used to describe the charge density distribution within an unrestricted stream of collisionless plasma, such as the solar wind. It also analyzes non-exponential solutions of the Poisson equation for plasma sheaths above flat surfaces, from which such a flow takes off and on which it falls, obtained in quadratures.

Ab-initio insights into the mechanical, phonon, bonding, electronic, optical and thermal properties of hexagonal W2N3 for prospective applications

We thoroughly investigated the structural, mechanical, electronic, vibrational, optical, thermodynamic, and a number of thermophysical properties of W2N3 compound through first-principles calculations using the DFT based formalism. The calculated structural parameters show very good agreement with the available theoretical and experimental results. The mechanical and dynamical stabilities of this compound have been investigated theoretically from the elastic constants and phonon dispersion curves. The Pugh's and Poisson's ratios of W2N3 are located quite close to the brittle/ductile borderline. W2N3 is elastically anisotropic. The calculated electronic band structure and density of states reveal that W2N3 is conducting in nature. The Fermi surface topology has also been explored. The analysis of charge density distribution map shows that W atoms have comparatively high electron density around compared to the N atoms. Presence of covalent bondings between W–N, W–W, and N–N atoms are anticipated. High melting temperature and high phonon thermal conductivity of W2N3 imply that the compound has potential to be used as a heat sink system. The optical characteristics show anisotropy. The compound can be used in optoelectronic devices due to its high absorption coefficient and low reflectivity in the visible to ultraviolet spectrum. Furthermore, the quasi-harmonic Debye model is used to examine temperature and pressure dependent thermal characteristics of W2N3 for the first time.