Charge Distribution Function Research Articles

DIFFERENT APPROACHES FOR DESCRIPTION OF NEGATIVE ION FORMATION IN AN ARGON/ACETYLENE PLASMA AFTERGLOW

Properties of an Ar/C2H2 plasma afterglow with dust particles are investigated at different assumptions concerning negative ion formation. First, numerical calculations are carried out assuming that C2nH2− negative ions, where n is a natural number, are the dominant anions in the plasma afterglow (the case (i)). Second, the studies are conducted assuming that C2nH− anions are only the negative ions, which are present in the afterglow plasma (the case (ii)). It is shown that the total density of negative ions n_ in the case (ii) is smaller than n_ in the case (i). Due to smaller n_, the positive ion densities are smaller and the absolute values of the mean dust charge and its variances are larger in the case (ii) than the corresponding values calculated using the approach (i). We also calculated the dust charge distribution functions (DCDFs) for late afterglow times. It is found that the DCDFs obtained in the case (ii) are shifted to the region of larger negative charges comparing with the dust charge distributions obtained in the case (i). The differences are mainly due to the loss of C2nH − anions in collisions with H atoms in the case (ii). In the case when the loss of negative ions in collisions with H atoms is not taken into account in the models, the both approaches give nearly the same time dependences for positive and negative ion densities, electron density, mean dust charge and its variance.

Modified Debye-Hückel-Onsager theory for electrical conductivity in aqueous electrolyte solutions: Account of ionic charge nonlocality.

This paper presents a mean field theory of electrolyte solutions, extending the classical Debye-Hückel-Onsager theory to provide a detailed description of the electrical conductivity in strong electrolyte solutions. The theory systematically incorporates the effects of ion specificity, such as steric interactions, hydration of ions, and their spatial charge distributions, into the mean-field framework. This allows for the calculation of ion mobility and electrical conductivity, while accounting for relaxation and hydrodynamic phenomena. At low concentrations, the model reproduces the well-known Kohlrausch's limiting law. Using the exponential (Slater-type) charge distribution function for solvated ions, we demonstrate that experimental data on the electrical conductivity of aqueous 1:1, 2:1, and 3:1 electrolyte solutions can be approximated over a broad concentration range by adjusting a single free parameter representing the spatial scale of the nonlocal ion charge distribution. Using the fitted value of this parameter at 298.15K, we obtain good agreement with the available experimental data when calculating electrical conductivity across different temperatures. We also analyze the effects of temperature and electrolyte concentration on the relaxation and electrophoretic contributions to total electrical conductivity, explaining the underlying physical mechanisms responsible for the observed behavior.

Formation of solid electrolyte interphase in Li-ion batteries: Insights from temperature-accelerated ReaxFF molecular dynamics

The solid electrolyte interphase (SEI) forms between anode and electrolyte in the lithium-ion battery (LIB) and is considered to be the main contributor to LIB degradation. To understand the degradation and SEI formation, we use reactive force-field (ReaxFF) molecular dynamics to gain atomic level insights into the key phenomena. We report the effect of different reaction temperatures on SEI formation on the lithium metal anode surface in contact with pure ethylene carbonate electrolyte. The temperature elevation is found to boost the SEI formation. To investigate the structural variations of SEI, we compare the quantitative variations of key species and perform analysis using the charge distribution and radial distribution function (RDF). Our work reveals that elevated temperature of up to 700 K is appropriate for acceleration of chemical reactions during SEI formation. The study provides insights into structural variations of the lithium metal electrode and SEI at the molecular level, demonstrating that temperature-accelerated reactive molecular dynamics is an efficient and effective tool for predicting the performance and degradation of the Li-ion batteries.

Plasma properties and discharging of dust particles in an Ar/C2H2 plasma afterglow

A global (volume averaged) model is developed for an argon-acetylene plasma afterglow. The model is used to study the electron and ion densities, electron temperature and densities of argon metastable atoms in the afterglow plasma. The calculated time dependence for the electron density is found to be in agreement with the existing experimental data. These calculated plasma characteristics are used to investigate the dust charge distribution function (DCDF) for particles with radii of 10–200 nm. The DCDF is found by solving numerically the master equation describing dust discharging as a one-step stochastic process and is also calculated as a Gaussian distribution with mean dust charge and variance, which are functions of time. The time dependences for mean dust charge, variance and dust charging time are obtained and analysed. If the electronegativity of the plasma in the steady-state is low, negative ions do not affect much discharging of dust particles in the afterglow, while at large electronegativity their role is essential. In the case of low electronegativity, discharging of dust particles is mainly due to deposition of positive ions with small and moderate masses (less than the mass of C10H6 + ions). Increasing electronegativity, the effect of heavy positive ions on dust discharging in the late afterglow is important. Secondary electron emission from dust surface at collisions of metastable atoms appears to be negligible.

Viscoelasticity of globular protein-based biomolecular condensates.

The phase separation of biomolecules into biomolecular condensates has emerged as a ubiquitous cellular process. Understanding how intrinsically disordered protein sequence controls condensate formation and material properties has provided fundamental biological insights and led to the development of functional synthetic condensates. While these studies provide a valuable framework to understand subcellular organization via phase separation they have largely ignored the presence of folded domains and their impact on condensate properties. We set out to determine how the distribution of sticker interactions across a globular protein contributes to rheological properties of condensates and to what extent globular protein-containing condensates differ from those formed from two disordered components. We designed three variants of green fluorescent protein with different charge patterning and used dynamic light scattering microrheology to measure the viscoelastic spectrum of coacervates formed with poly-lysine over a timescale of 10-6 to 10 seconds, elucidating the response of protein condensates in this range for the first time. We further showed that the phase behavior and rheological characteristics of the condensates varied as a function of both protein charge distribution and polymer/protein ratio, behavior that was distinct to condensates formed with folded domains. Together, this work enhances our fundamental understanding of dynamic condensed biomaterials across biologically relevant length- and time-scales.

Modifying the electronic and magnetic properties of the scandium nitride semiconductor monolayer via vacancies and doping.

In this work, the effects of vacancies and doping on the electronic and magnetic properties of the stable scandium nitride (ScN) monolayer are investigated using first-principles calculations. The pristine monolayer is a two-dimensional (2D) indirect-gap semiconductor material with an energy gap of 1.59(2.84) eV as calculated using the GGA-PBE (HSE06) functional. The projected density of states, charge distribution, and electron localization function assert its ionic character generated by the charge transfer from the Sc atoms to the N atoms. The monolayer is magnetized by a single Sc vacancy with a total magnetic moment of 3.00μB, while a single N vacancy causes a weaker magnetization with a total magnetic moment of 0.52μB. In both cases, the magnetism originates mainly from the atoms closest to the defect site. Significant magnetization is also reached by doping with acceptor impurities. Specifically, a total magnetic moment of 2.00μB is obtained by doping with alkali metals (Li and Na) in the Sc sublattice and with B in the N sublattice. Doping with alkaline earth metals (Be and Mg) in the Sc sublattice and with C in the N sublattice induces a value of 1.00μB. In these cases, either magnetic semiconducting or half-metallicity characteristics arise in the ScN monolayer, making it a prospective 2D spintronic material. In contrast, no magnetism is induced by doping with donor impurities (O and F atoms) in the N sublattice. An O impurity metallizes the monolayer; meanwhile, F doping leads to a large band-gap reduction of the order of 82%, widening the working regime of the monolayer in optoelectronic devices. The results presented herein may introduce efficient methods to functionalize the ScN monolayer for optoelectronic and spintronic applications.

Structure and Dynamics of the Electrical Double Layer during the Rapid Alternating Polarity Electro-Synthesis

Conventional electrochemical organic synthesis uses direct current (DC) condition, where the electrode polarity is not changed during the operation. Unlike DC, alternating current (AC) introduces two more tunable parameters into the potential or current profile: frequency and waveform, allowing new possibilities for modulating reaction efficiency and selectivity. Several very recent AC electrosynthesis examples have shown that the AC can lead to enhanced chemoselectivity that cannot be reproduced by their DC counterparts1–3. For instance, Hayashi et al. presented a highly selective and easily scalable Birch-type reduction of heteroarenes by rapid alternating polarity (rAP) waveform3. AC voltage transforms the reaction kinetics presumably by affecting the mass transfer of reactive species both in the bulk solution and the electrical double layers (EDL). However, the mechanistic origin of the unique reactivity in AC electrosynthesis is underexplored. Molecular-level details are still in lack to possibly guide the rational design of AC reaction parameters.In this study, we have chosen the rAP heteroarene reduction as the example system and employed classical molecular dynamics (MD) simulations to reveal the liquid structure and dynamics in bulk and interfacial electrolyte. To capture the electrode-electrolyte interfaces, a slab-geometry simulation cell was used, where a 10 nm thick liquid electrolyte is sandwiched between two oppositely charged graphene surfaces. The multicomponent electrolyte was composed of ethanol and tetrahydrofuran (THF) as the co-solvent, [(CH3)4N]+[(BF4)]- as the salt, and a heteroarene substrate. Based on the charge distribution function statistics, the EDL layer was about 1 nm thick, so if any of the oxygen atom in the ethanol or THF is within 6 Å to the electrode surface, they are considered to be within the EDL. Under both AC and DC, the ethanol to THF ratio was higher than that in the bulk electrolyte due to stronger ion-ethanol attraction. The EDL structure responded to electric field polarity change at different time scales. First, the molecule orientation would flip also within the picosecond time scale after the polarity switch. By tracking the number of molecules in the EDL, we have found that the compositional fluctuation in the EDL converges in about 40 ps. Although it is the ion migration that gets directly affected by the alternating electric field, diffusion of charge-neutral molecules was also found to be accelerated under AC, according to the higher mean squared displacement calculated from the movement of all molecules of each species in the simulation box. This accelerated diffusion spans a larger length and longer time scales. A multi-scale model is proposed to describe both reaction kinetics and liquid structure dynamics simultaneously.

A New Electron Charge Distribution Function of Electron

Here we derive a new charge distribution function for an electron by using as an equation of motion a segment of charge whose self energy interaction is due to electric field potential. Our method is based on the consideration that a charged distribution function should be represented as an eigenfunction of electron mass energy. We compare our electron charge distribution function to that of Weinberg’s η(r) and our charged electron radius to that obtained by Kim.

DISCHARGING OF DUST PARTICLES OF DIFFERENT SIZES IN AN ARGON AFTERGLOW PLASMA

The dust charge distribution function (DCDF) in an argon plasma afterglow is obtained by solving numerically the master equation describing dust discharging as a one-step stochastic process. The calculated DCDFs are compared with Gaussian distributions, and it is found that the dust charge distribution functions can be approximated quite well by the latter ones for different external conditions. It is found how the DCDF, mean dust charge, variance and charging time depend on dust size. For late afterglow times, it is also analyzed how the emission of electrons in the collisions of excited argon atoms with dust particles affects the DCDF. It is shown that the emission effect is more essential for larger nanoparticles than for smaller ones.

Modeling results on the dust charge distribution in a plasma afterglow

Discharging of dust particles in an argon plasma afterglow is investigated using different approaches. First, the dust charge distribution function (DCDF) is obtained by solving numerically the master equation describing dust discharging as a one-step stochastic process. Second, the DCDF is calculated as a Gaussian distribution with mean dust charge and variance, which are functions of time. Additionally, the time-dependencies for the mean dust charge are obtained assuming that the charge changes continuously in the afterglow plasma. Calculation results are compared with available experimental data and are found to be in good qualitative agreement if the dust discharging model accounts for the emission of electrons in the collisions of excited argon atoms with dust particles. This study is carried out taking into account the transition from ambipolar to free diffusion as well as multistep ionization, excitation, and deexcitation of argon atoms in the plasma afterglow.

Electronic properties of the GaN nanowires surface activated by Cs/Li/NF3/Cs/Li alternate method in a high-concentration residual gas environment

The characteristics of models that adsorb different concentrations of H2O and CO2 residual gases on the surface of GaN nanowires activated alternately by Cs/Li/NF3/Cs/Li investigated systematically using first-principles, including adsorption energy, atomic structure, and work function, electron affinity and dipole moment. For the Cs/Li/NF3/Cs/Li alternately activated surface, H2O molecules are more likely to remain on the surface than CO2 molecules. In a high-concentration residual gas atmosphere, Cs/Li/NF3/Cs/Li alternately activated surface can be more stable than pure p-type surfaces. However, high concentrations of H2O and CO2 gas have a destructive effect on the activation layer, and it can even make the activated surface lose its negative electron affinity. The newly generated dipole moment from Cs and Li atoms to residual gas molecules greatly affects the normal operation of the cathode activation layer. From the analysis of characteristic data such as charge distribution and work function, the alternately activated cathode needs to work in a high vacuum state as much as possible to avoid generating a high-concentration residual gas environment.

In English

Development of theoretical tools to analyze electronic structure of complex nanomaterials depending on features of spatial and chemical organizations of different phases is of interest from both practical and theoretical points of view. Therefore, in this work, an approach based on computations of the atomic charge distribution functions (CDF) in parallel to calculations of the distribution functions of the chemical shifts (SDF) of protons is developed to be applied to a set of complex oxide and carbon nanomaterials. Binary nanooxides (alumina/silica, titania/silica), 3d-metal-doped anatase, activated carbon, carbon nanotube, fullerene C60, graphene oxide, and N-doped Kagome graphene are considered here as representatives of different classes of nanomaterials. The analyses of the CDF and SDF as nonlocal characteristics of certain kinds of atoms in complex systems provide a deeper insight into electronic structure features depending on composition of the materials, guest phase-doped host phase at various amounts of dopants, structure of O- and OH-containing surface sites, amounts and organization of adsorbed water, formation of neutral and charged surface functionalities, bonding of solvated ions, etc. The CDF of metal and hydrogen atoms (electron-donors) are more sensitive to the mentioned factors than the CDF of O, N, and C atoms (electron acceptors) in various systems. As a whole, the use of the CDF and SDF in parallel expands the tool possibility in detailed analysis of the structural and interfacial effects in dried and wetted complex nanomaterials.

Earth-mass primordial black hole mergers as sources for nonrepeating fast radio bursts

Fast radio bursts (FRBs) are mysterious astronomical radio transients with extremely short intrinsic duration. Until now, the physical origins of them still remain elusive especially for the non-repeating FRBs. Strongly inspired by recent progress on possible evidence of Earth-mass primordial black holes, we revisit the model of Earth-mass primordial black holes mergers as sources for non-repeating FRBs. Under the null hypothesis that the observed non-repeating FRBs are originated from the mergers of Earth-mass primordial black holes, we analyzed four independent samples of non-repeating FRBs to study the model parameters i.e. the typical charge value $q_{\rm{c}}$ and the power index $\alpha$ of the charge distribution function of the primordial black hole population $\phi(q) \propto (q/q_{\rm{c}})^{-\alpha}$ which describe how the charge was distributed in the population. $q$ is the charge of the hole in the unit of $\sqrt{G} M$, where $M$ is the mass of the hole. It turns out that this model can explain the observed data well. {Assuming the monochromatic mass spectrum for primordial black holes}, we get the average value of typical charge $\bar{q}_{\rm{c}}/10^{-5}=1.59^{+0.08}_{-0.18}$ and the power index $\bar{\alpha}=4.53^{+0.21}_{-0.14}$ by combining the fitting results given by four non-repeating FRB samples. The event rate of the non-repeating FRBs can be explained in the context of this model, if the abundance of the primordial black hole populations with charge $q \gtrsim 10^{-6}$ is larger than $10^{-5}$ which is far below the upper limit given by current observations for the abundance of Earth-mass primordial black holes. In the future, simultaneous detection of FRBs and high frequency gravitational waves produced by mergers of Earth-mass primordial black holes may directly confirm or deny this model.

Eulerian formulation for the triboelectric charging of polydisperse powder flows

We propose an Eulerian formulation for the triboelectric charging of powder flows. Recently, continuum descriptions of the charging of monodisperse and bidisperse powder appeared. Now, we propose the first Eulerian formulation for this type of flows that can fully account for polydisperse particle size distributions. To this end, the joint particle size, velocity, and charge distribution function are solved through the direct quadrature method of moments. The newly established approach includes the uptake of electrostatic charge by the particles when contacting a solid wall and the exchange of charge in-between particles during collisions. The electrostatic field induced by the charge of the particles and the drag forces of the surrounding gas affects the particle dynamics. Test cases of two-dimensional steady channel flows demonstrate the charging of the flow from the walls toward the center and in the downstream direction. Further, the method predicts the effect of variations of the particle size and initial velocity distribution and the charge diffusion coefficient. The ability to handle polydispersity is a step toward the simulation of the electric charge buildup of real powder flows in full-scale technical applications.

Effects of layer-charge distribution on swelling behavior of mixed-layer illite-montmorillonite clays: A molecular dynamics simulation study

One of the intriguing properties of clay minerals is swelling, which is considered an essential characteristic for various geological processes, environmental science, and engineering. Almost all previous experimental and simulation studies focused on the understanding of the swelling behavior of pure clays. The fact is that about 30 percent of all clays are a pure type, and virtually 70 percent of clays are the mixed-layer one that swelling mechanism is still elusive. In this research, molecular dynamics simulations were used to exclusively investigate the effect of layer charge distribution on the crystalline swelling and hydration behavior of the most common types of mixed clays, so-called illite-montmorillonite mixed-layer clay (I-Mt MLC) with Na+ and K+ counterions in the presence of different water concentrations. Based on the results, we found that the layer charge density and charge location of both illite and Mt significantly influenced the I-Mt clays' swelling behavior. Regardless of Mt charge density, the presence of highly charged illite led to powerful interactions of counterions with the surface sheet, resulting in less swelling behavior of the I-Mt system. Also, the various polarization power of clay surface due to the difference in charge distribution of octahedral sheets had a significant influence on water molecules and interlayer cations interaction with clay surface, which affected the swelling behavior of I-Mt clays. Overall, our findings demonstrated the new insight into I-Mt clays' swelling behavior, which is a function of charge distribution of both illite and Mt.

Atomic charge distribution functions as a tool to analyze electronic structure of molecular and cluster systems

AbstractA set of the characteristics calculated using any quantum chemical method can be attributed to local electronic structure, which may change for each atom in complex systems. Related average values can give poor characteristics because different atom fractions with different surroundings may have different electronic characteristics poorly corresponding to the average values. The aim of this work is to show that the distribution functions of atomic charges, as well as chemical shifts and molecular orbital energies, can be considered as a set of simple tools for easy analysis of complex systems within the scope of nonlocal characteristics describing whole systems. The approach efficiency and analysis adequacy depend on appropriateness of molecular and cluster models used. The systems with dozens or hundreds of molecules and solid nanoparticles of almost real sizes (>40 units, >2 nm) or calculated with periodic boundary conditions and expanded cells give more adequate nonlocal characteristics than much smaller systems with several molecules and small clusters (<10 units, <1 nm) can give.

Quantum Modelling of Nanoscale Silicon Gate-All-Around Field Effect Transistor

The paper introduces an analytical model for gate all around (GAA) or Surrounding Gate Metal Oxide Semiconductor Field Effect Transistor (SG-MOSFET) inclusive of quantum mechanical effects. The classical oxide capacitance is replaced by the capacitance incorporating quantum effects by including the centroid parameter. The quantum variant of inversion charge distribution function, inversion layer capacitance, drain current, and transconductance expressions are modeled by employing this model. The established analytical model results agree with the simulated results, verifying these models' validity and providing theoretical supports for designing and applying these novel devices.

Analytical Quantum Model for Germanium Channel Gate-All-Around (GAA) MOSFET

The paper proposes analytical model for Gate-All-Around Metal Oxide Semiconductor Field Effect Transistor (GAA-MOSFET) for germanium channel including quantum mechanical effects. It is achieved by solving coupled Schrodinger-Poisson’s equation using variational approach. The proposed model takes quantum confinement effects to obtain charge centroid and inversion charge model. By using these models the quantum version of inversion layer capacitance, inversion charge distribution function and Drain current expressions are modelled and the performance evaluation of the developed model is compared with Silicon channel GAA-MOSFET. Analytically modelled expressions are verified by comparing the model with simulation results.

Strain-induced band modulation of surface F-functionalized two-dimensional Sc2C

Abstract Two-dimensional (2D) materials have recently gained tremendous interest in the application of potential electrode materials, and sensor materials. In this paper, strain-induced band modulation and migrant mechanism of monolayer Sc2CF2 under biaxial strain are investigated theoretically. Our investigation reveals that Sc2CF2 is stable under strain because of the negative Ecoh. Sc2CF2 can sustain a stress up to 8.35 N/M, which corresponds to the tensile strain limit of about 23%. All the considered strains are within the elastic limit. Sc2CF2 undergoes a semiconductor to metal transition because of the left shift of Sc-d states induced by −10% strain. The critical point from the indirect gap (M to Γ) to direct gap (M to M) is about 14%, after which the band gap decreases with the increasing tensile strain. We found that the decreasing contribution of Sc atom at valence band maximum (VBM) and conduct band minimum (CBM) states is favorable for the formation of direct band gap under tensile strain and for the transition of semiconductor to metal under compression strain. There exist strong Sc C and Sc F interaction under strain through the analysis of spatial charge distribution and electron localization function.

Trace Formula for a High-Order Differential Operator on an Interval under a Perturbation of the Lower-Order Term by a Finite Charge

In this paper, a regularized trace formula is obtained for a higher-order differential operator on an interval under a perturbation of the lower-order term by a finite charge. Arbitrary regular boundary conditions and an arbitrary order n ⩾ 3 of the operator are considered. A new effect is discovered: for an even order of the operator, an additional term appears depending on the jump of the charge distribution function at the midpoint of the interval.