Charge Density Distribution Research Articles

Crystal structure and physical properties of Ti2B5 predicted by first principles calculations

Applying the advanced CALYPSO structure searching method and first principles calculations, we predict a novel superhard structure for Ti2B5, which belongs to the monoclinic C2/m space group. The previously known Hf2B5, W2B5, and δ-V2O5-type structures are also selected as the potential structures for Ti2B5. It is shown that the predicted C2/m structure is the most stable phase among these considered structures within the range of 0-100GPa. The calculations of the phonon dispersion and elastic constants affirm that the predicted C2/m phase is dynamically and mechanically stable. The predicted high shear modulus (249 GPa) and large hardness (46.9 GPa) show that it should be anunderlying superhard material. In addition, the elastic anisotropy of Ti2B5 is also explored by investigating the directional dependence of the Young's modulus, shear modulus, and Poisson's ratio as well as some well anisotropy indices. The particular analyses of the density of states and electron charge density distribution verify that the strong B-B and Ti-B covalent bonds in the predicted C2/m-Ti2B5 phase playan importantpartin its hardness and structural stability.

Crystallization Engineering of CuNi2 S4 Ultra-Fine Nanocrystals with Optimized Band Structures for Efficient Photocatalytic Pollutant Degradation and Hydrogen Production.

The mono-dispersed cubic siegenite CuNi2 S4 ultra-fine (≈5nm) nanocrystals are fabricated through crystallization engineering under hot injection. The strong hydroxylation on mostly exposed CuNi2 S4 (220) surface leads to the formation of multi-valence (Cu+ , Cu2+ , Ni2+ , Ni3+ ) species with unsaturated hybridization and coordination micro-environments, which can induce rich redox reactions to optimize interfacial kinetics for the adsorbed reaction intermediates. The as-synthesized CuNi2 S4 nanocrystals with ultra-small particle size and the characteristics of being highly dispersed can increase specific surface area and hydroxylated active sites, which considerably contribute to the improvement of photocatalytic activities. Experimental and theoretical studies indicate that the CuNi2 S4 with unique surface condition can properly modulate the charge density distribution and the electronic band structure, thus achieving an optimal band gap for enhancing visible light absorption. Additionally, the strong hydroxylation on CuNi2 S4 (220) surface can not only make the photocatalytic process stable in alkaline environment but also bring about an impurity level between conduction and valence band, which facilitates the separation of photo-induced charge carriers by suppressing the rapid re-combination of exited electrons and holes. The optimization of band structure should be the intrinsic reason for the efficient photocatalytic pollutant degradation and hydrogen production under visible light illumination.

A comprehensive ab-initio insights into the pressure dependent mechanical, phonon, bonding, electronic, optical, and thermal properties of CsV3Sb5 Kagome compound

In this paper, we have presented a comprehensive study of the physical properties of Kagome superconductor CsV3Sb5 using the density functional theory (DFT) methodology. The structural, mechanical, electronic properties (band structure, electronic energy density of states, Fermi surface, and charge density distribution), atomic bonding, hardness, thermodynamics, optical properties, and their pressure dependences have been investigated systematically at different pressures. The calculated ground state lattice parameters and volume are in excellent agreement with available experimental results. The estimated single-crystal elastic constants ensured the mechanical stability of the compound, whereas phonon spectra endorse dynamical stability at zero pressure. The electronic band structure, density of states, and optical properties confirmed the metallic feature. The Pugh ratio and Poisson’s ratio of the compound under study revealed the softness/ductility. The hardness of CsV3Sb5, estimated using several formulae, is quite low while the machinability index predicted good machinability with excellent lubricating properties. The compound shows tendency towards structural instability at a pressure around 18 GPa. The optical constants have also been studied to correlate them with electronic properties (band structure) and predict the possible applications of this compound. Both the mechanical and optical properties show directional anisotropy. CsV3Sb5 is predicted to be an efficient absorber of ultraviolet radiation. The compound is also an efficient reflector of visible light. The superconducting transition in CsV3Sb5 has been revisited following prior studies.

Research of the effect of different corrugated dust collection plates on particle removal in electrostatic precipitators

In this paper, a multi-physics field coupled model of electric, flow and particle fields was constructed by COMSOL to compare the effects of three different corrugated dust collector plates on electric field distribution, airflow field, particle trajectories and dust removal efficiency in an electrostatic precipitator, and to compare them with a conventional electrostatic precipitator with a parallel plate structure. The results indicated that the corrugated dust collection plate influenced the electric field within the ESP channel, while the wire plate spacing directly affected the size and distribution of space charge density. Furthermore, the corrugated dust collection plate also affected the EHD flow within the channel, with the D2-ESP and D3-ESP being the most strongly influenced by the ionic wind. By comparing the dust removal efficiency of the four ESPs, we found that D2-ESP has the highest dust removal efficiency, followed by D3-ESP, then Flat-ESP, and finally D1-ESP. The ranking order of the four ESPs' dust removal efficiency is consistent with the ranking order of the space charge density within the four ESP channels, which shows that the size of the space charge density directly affects the dust removal efficiency of ESPs. Numerical simulation results show that the change of wire plate spacing is the main reason why corrugated ESP affects the dust removal efficiency of electrostatic precipitators.

Phosphorus-Mediated Local Charge Distribution of N-Configuration Adsorption Sites with Enhanced Zincophilicity and Hydrophilicity for High-Energy-Density Zn-Ion Hybrid Supercapacitors.

Tailor-made carbonaceous-based cathodes with zincophilicity and hydrophilicity are highly desirable for Zn-ion storage applications, but it remains a great challenge to achieve both advantages in the synthesis. In this work, a template electrospinning strategy is developed to synthesize nitrogen and phosphorous co-doped hollow porous carbon nanofibers (N, P-HPCNFs), which deliver a high capacity of 230.7 mAh g-1 at 0.2 A g-1 , superior rate capability of 131.0 mAh g-1 at 20 A g-1 , and a maximum energy density of 196.10Wh kg-1 at the power density of 155.53W kg-1 . Density functional theory calculations (DFT)reveal that the introduced P dopants regulate the distribution of local charge density of carbon materials and therefore facilitate the adsorption of Zn ions due to the increased electronegativity of pyridinic-N. Ab initio molecular dynamics (AIMD)simulations indicate that the doped P species induce a series of polar sites and create a hydrophilic microenvironment, which decreases the impedance between the electrode and the electrolyte and therefore accelerates the reaction kinetics. The marriage of ex situ/in situ experimental analyses and theoretical simulations uncovers the origin of the enhanced zincophilicity and hydrophilicity of N, P-HPCNFs for energy storage, which accounts for the faster ion migration and electrochemical processes.

Research on the Forward Solving Method of Defect Leakage Signal Based on the Non-Uniform Magnetic Charge Model.

Pipeline magnetic flux leakage inspection is widely used in the evaluation of material defect detection due to its advantages of having no coupling agent and easy implementation. The quantification of defect size is an important part of magnetic flux leakage testing. Defects of different geometrical dimensions produce signal waveforms with different characteristics after excitation. The key to achieving defect quantification is an accurate description of the relationship between the magnetic leakage signal and the size. In this paper, a calculation model for solving the defect leakage field based on the non-uniform magnetic charge distribution of magnetic dipoles is developed. Based on the traditional uniformly distributed magnetic charge model, the magnetic charge density distribution model is improved. Considering the variation of magnetic charge density with different depth positions, the triaxial signal characteristics of the defect are obtained by vector synthesis calculation. Simultaneous design of excitation pulling experiment. The leakage field distribution of rectangular defects with different geometries is analyzed. The experimental results show that the change in defect size will have an impact on the area of the defect leakage field distribution, and the larger the length and wider the width of the defect, the more sensitive the impact on the leakage field distribution. The solution model is consistent with the experimentally obtained leakage signal distribution law, and the model is a practical guide by which to improve the quality of defect evaluation.

Anisotropic hybridization probed by polarization dependent x-ray absorption spectroscopy in VI3 van der Waals Mott ferromagnet

Polarization dependent x-ray absorption spectroscopy was used to study the magnetic ground state and the orbital occupation in bulk-phase VI3 van der Waals crystals below and above the ferromagnetic and structural transitions. X-ray natural linear dichroism and x-ray magnetic circular dichroism spectra acquired at the V edges are compared against multiplet cluster calculations within the frame of the ligand field theory to quantify the intra-atomic electronic interactions at play and evaluate the effects of symmetry reduction occurring in a trigonally distorted VI6 unit. We observed a non zero linear dichroism proving the presence of an anisotropic charge density distribution around the V3+ ion due to the unbalanced hybridization between the vanadium and the ligand states. Such hybridization acts as an effective trigonal crystal field, slightly lifting the degeneracy of the ground state. However, the energy splitting associated to the distortion underestimates the experimental band gap, suggesting that the insulating ground state is stabilized by Mott correlation effects rather than via a Jahn–Teller mechanism. Our results clarify the role of the distortion in VI3 and establish a benchmark for the study of the spectroscopic properties of other van der Waals halides, including emerging 2D materials with mono and few-layers thickness, whose fundamental properties might be altered by reduced dimensions and interface proximity.

Experimental and theoretical vibrational spectral Investigations, structural conformations, DFT estimations and docking studies of antibacterial drug Nitrilotriaceticacid

Nitrilotriaceticacid (NTA) was utilised without additional purification after being bought from Sigma Aldrich Chemical Company in powdered form with 99% purity. Density Functional Theory calculations at B3LYP with a 6-311++G (d,p) level were performed to gain knowledge of molecule geometries, harmonic vibrational spectra, and molecular docking analysis. Vibrational spectral investigations have been carried out with the aid of Normal Coordinate Analysis on the basis of potential energy distribution (PED) of each mode, which helps us to attain a quantitative as well as qualitative analysis of IR and Raman spectra followed by empirical scaled quantum mechanical force field methodology. Natural bond orbital analysis, Fukui analysis, RDG analysis, and Mulliken’s net charges have also been predicted. FMO's energy gap predicts the occurrence of charge transport within molecule. UV–Visible spectral analyses of NTA have been examined by experimental and theoretical calculations. By mapping electron density isosurface with an electrostatic potential surface (ESP), information about the size, shape, charge density distribution, and site of chemical reactivity of the molecules has been acquired. ELF and LOL maps portrayed topological aspects of NTA which also have been depicted. Hyperpolarizability values are in good agreement revealing that these compounds could be employed in electro optical applications. Antibacterial activity reveals that NTA have been found to exhibit antibacterial effects. Docking simulation has been carried out for the optimized ligand molecule to identify binding energy and coupling with protein molecule. NTA molecule underwent a drug likeness test utilising Lipinski's criterion, and using ADMET contour, the molecule is recommended for inclusion in pharmaceuticals.

Shorter-chained trialkylsulfonium cations are preferable as admixtures to lithium-ion and sodium-ion electrolytes in acetonitrile

The development and improvement of electrolytes is a persisting research agenda in the context of electrochemical energy sources. The sodium-ion is a possible and partial substitute for Li-ion in alkali ion batteries of the future. Many large-scale applications urge electrolytes featuring a competitive interplay of ionic conductivity, shear viscosity, and cohesion energy. The general applicability of sulfonium ionic liquids (ILs) reinforced with Li-ions to energy storage was experimentally exemplified in recent years. Herein, we employed potential energy surface exploration bundled with electronic-structure simulations to shed light on the ion-ionic and ion-molecular interactions in perspective electrolyte systems involving trialkylsulfonium cation, Li/Na salts, and acetonitrile (ACN). By analyzing a wealth of supramolecular conformations and characterizing them via thermodynamics, structure, charge density distributions, electrostatic potential surfaces, atom–atom couplings, and reactivity descriptors, we outline the most promising sulfonium-based electrolytes. We provide a critical discussion of the future of sodium-ion batteries and compare them to lithium-ion batteries directly. The oxygen atoms of bis(trifluoromethanesulfonyl)imide anion [TFSI] coordinate Li+ and Na+ to remarkably various extents. Surprisingly, the size of the chosen trialkylsulfonium-based cation impacts the ion-ionic interactions weakly, contrary to expectations. Whereas the difference between the behavior of the Li-ion and Na-ion is paramount irrespective of all other components and their stationary points. [TFSI] was confirmed to be a highly flexible chemical structure although its conformations (one cis and two trans) were unraveled to differ only within an amount of thermal energy at room conditions. The reported discussion drives ongoing trials of the alkali-ion electrolytes based on sulfonium ILs and ACN.

Electronic Interpretation of Interlayer Energy Landscape in Layered Materials

AbstractThe interlayer energy landscape of layered materials is essential to disassemble their structure–property relationships. However, a clear definition of interlayer electronic coupling that generally rules the interlayer energy landscape for their outstanding electronic and tribological properties, remains a matter of debate. Herein, diverse methods for electron coupling are evaluated to discriminate their feasibility to interpret interlayer sliding energy landscape for frictional sliding or stacking faults, by using density functional theory calculation of the layered models in the case of transition metal dichalcogenides (TMDs). It is discovered that the charge density evolution in dynamic stacking configurations dictates the interlayer energy landscape along the sliding pathway, challenging the prevailing belief that the energy corrugation arises from the nonuniform distribution of charge density or the charge density in the interface region. The present studies may open the way to disassemble the electron coupling principle underlying interlayer energy landscape for structure–property relationships as stacking faults, registry effects, even superlubric behavior in layered structures.

Magnetic scattering with spin-momentum locking: Single scatterers and diffraction grating

Simultaneous manipulation of charge and spin density distributions in materials is the key element required in spintronics applications. Here we study the formation of coupled spin and charge densities arising in scattering of electrons by domains of local magnetization producing a position-dependent Zeeman field in the presence of the spin-momentum locking typical for topological insulators. Analytically and numerically calculated scattering pattern is determined by the electron energy, domain magnetization, and size. The spin-momentum locking produces strong differences with respect to the spin-diagonal scattering and leads to the scattering asymmetry with nonzero mean scattering angle as determined by only two parameters characterizing the system. To extend the variety of possible patterns, we study scattering by diffraction gratings and propose to design them in modern nanostructures based on topological insulators to produce desired distributions of the charge and spin densities. These results can be useful for engineering of magnetic patterns for electron optics to control coupled charge and spin evolution.

Theoretical and experimental spectroscopic studies and analysis for wave function on N-phenylmorpholine-4-carboxamide benzene-1,2-diamine with computational techniques

The present study focuses on structural and chemical analyses of N-phenylmorpholine-4-carboxamide benzene-1,2-diamine (PMCBD) using quantum computational methods. The calculated bond angle, length, and dihedral angle between atoms were compared with measured values. The observed and stimulated FT-IR (Fourier Transform Infrared Spectroscopy) spectra parameters for vibrational wavenumbers and their associated PED (Potential Energy Distribution) values in percentage have been obtained from VEDA4 software. The electronic transitions of PMCBD were discussed by TD-SCF/DFT/B3LYP based on the 6-311++G(d,p) basis set with solvents such as chloroform, ethanol, and dimethyl sulfoxide (DMSO) and gas. Density functional computations were used to study the band energy between HOMO and LUMO using the B3LYP/6-311++G(d,p) level. Mulliken analysis and natural population analysis were used for a better understanding of charge levels on different atoms such as N, H and O. The natural bonding orbital (NBO) analysis proved helpful in studying molecular and bond strengths. (NBO). The ESP acquired data on the molecule's size, shape, charge density distribution, and chemical reactivity site. This was done by mapping electron density on the surface with electrostatic potential. Non-linear optical detection of PMCBD was also discussed. Aside from the electron localization function map, state densities are also mapped using Multiwfn software, a wave function analyzer.

Accelerated mass/electron transfer by self-supporting Ni2P@Cu3P heterostructure array to boost alkaline hydrogen evolution at high current density

The construction of hydrogen evolution reaction (HER) catalysts at high current density (HCD) is challenging. Electron/mass transfer is hindered by the unsatisfied electrical conductivity at the catalyst-support interface and the massive gas bubbles adhered at the electrolyte-catalyst interface at HCD condition. Herein, a non-precious Ni2P@Cu3P heterostructure constructed by in-situ phase conversion is developed as an electrochemical HER catalyst. The Ni(OH)2 decorated Cu(OH)2 nanowire heterostructure is completely converted into the high electrical conductive Ni2P@Cu3P by a simple phosphatizing method, which not only remain the 3D nanowire array structure but also provide the large specific active surface area and plentiful channels for the fast charge/mass transport to accelerate the HER dynamics. Furthermore, density functional theory calculations reveal that the strong electron interaction between the Ni2P and Cu3P, which can regulate the charge density distribution. As-prepared Ni2P@Cu3P heterostructure displays a more moderate free energy (ΔGH2O = -0.37 eV and ΔGH* = −0.01 eV) for alkaline HER. Benefiting from the complementary advantage of Ni2P and Cu3P, the Ni2P@Cu3P heterostructure exhibits an enhanced HER activity with an overpotential of 279 mV, an excellent long-term stability and durability at 1000 mA·cm−2, providing the great potential for large-scale industrial applications.

Selective coordination of polyazin sapanisertib with halide vacancy for printable mesoscopic perovskite solar cells

The mitigation of under-coordinated Pb2+ (halide vacancy) defect remains an imperative challenge in the perovskite solar cells, especially printable mesoscopic perovskite solar cells (FP-PSCs). Here we report a commercial-available polyazin anticancer drug Sapanisertib as coordination passivator of halide vacancies in FP-PSCs, thereby achieving the photoelectric conversion efficiency (PCE) to 18.46%, along with a record certified PCE of 18.27%. In polazin Sapanisertib (Sap), there exists two kinds of nitrogen atoms: in-aromatic ring (in purine and oxazole rings, IAR-Ns) and out-aromatic ring (substituted amino groups, OAR-Ns). Through multiple characterizations, and DFT calculations show that substituted amino groups OAR-Ns hardly get interaction with the halide vacancy due to the distribution of charge density in Sapanisertib. Our work suggests that the selective coordination is of great significance for the design of high-performance passivators for printable mesoscopic perovskite solar cells.

Electronic structures and Aharonov–Bohm effect in higher-order topological Dirac Semimetal nanoribbons with strong confinements

Electronic structures and magnetotransport properties of topological Dirac semimetal (TDSM) nanoribbons are studied by adopting the tight-binding lattice model and the Landauer–Büttiker formula based on the non-equilibrium Green’s function. For concreteness, the TDSM material Cd3As2 grown along the experimentally accessible [110] crystallographic direction is taken as an example. We found that the electronic structures of the TDSM nanoribbon depend on both the strength and direction of the magnetic field (MF). The transversal local charge density (LCD) distribution of the electronic states in the TDSM nanoribbon is moved gradually from the center toward the hinge of each surface as a [010] direction MF strength is increased, forming the two-sided hinge states. However, one-sided surface states are generated in the TDSM nanoribbon when a [001] direction MF is applied. As a result, one-sided hinge states can be achieved once a tilted MF is placed to the TDSM nanoribbon. The underlying physical mechanism of the desired one-sided hinge states is attributed to both the orbital and Zeeman effects of the MF, which is given by analytical analyses. In addition, typical Aharonov–Bohm interference patterns are observed in the charge conductance of the two-terminal TDSM nanoribbon with a tilted MF. This conductance behaviour originates from the unique interfering loop shaped by the one-sided hinge states. These findings may not only further our understanding on the external-field-induced higher-order (HO) topological phases but also provide an alternative method to probe the HO boundary states.

Spatio‐temporal distributions of accumulated charge density in atmospheric pressure dielectric barrier discharges

AbstractThe effect of the secondary electron emission coefficient on accumulated charge density distributions in atmospheric pressure dielectric barrier discharges have been simulated using two‐dimensional fluid model. Spatio‐temporal distributions of accumulated charge density on each side of the dielectric have been examined. The differences of conventional waveforms of accumulated charge density and the simulated results were clarified. And when the dielectrics were negatively accumulated, charges were uniformly accumulated, while positive charges were not. Randomness of streamers' occurrence, and self‐organized structures have been also examined by the accumulated charge distributions.

A numerical solver for investigating the space charge effect on theelectric field in liquid argon time projection chambers

This paper reports the development of a numerical solver aimed to simulate the interaction between the space charge (i.e. ions) distribution and the electric field in liquid argon time projection chamber (LArTPC) detectors. The ion transport equation is solved by a time-accurate, cell-centered finite volume method and the electric potential equation by a continuous finite element method. The electric potential equation updates the electric field which provides the drift velocity to the ion transport equation. The ion transport equation updates the space charge density distribution which appears as the source term in the electric potential equation. The interaction between the space charge distribution and the electric field is numerically simulated within each physical time step. The convective velocity in the ion transport equation can include the background flow velocity in addition to the electric drift velocity. The numerical solver has been parallelized using the Message Passing Interface (MPI) library. Numerical tests show and verify the capability and accuracy of the current numerical solver. It is planned that the developed numerical solver, together with a Computational Fluid Dynamics (CFD) package which provides the flow velocity field, can be used to investigate the space charge effect on the electric field in large-scale particle detectors.

Distribution of Charges over the Surfaces of Charged Particles of Complex Shapes while Electrospraying

A current topical area of condensed matter physics is research in the field of structured materials that contain structures of micro- and nanoparticles. Electrospray is widely used to obtain micro- and nanoparticles. It is known to allow particles of different geometric shapes to be obtained. The authors propose an analytical procedure for obtaining a new class of nontrivial analytical solutions to the electrostatics problem of charge distribution over the surfaces of particles that can form while electrospraying. Complex nontrivial forms of this class of surfaces are considered. Exact analytical formulas are obtained for the charge distribution density over the surfaces of particles.

Spin-orbit coupling and electronic properties in Pt2MnGa: an ab-initio study

The electronic and magnetic properties of full-Heusler alloy Pt2MnGa with and without the effect of spin–orbit coupling are studied. The calculations have been carried out using ab initio density functional theory. Both the magnetic spin orders of Pt2MnGa, ferromagnetic and antiferromagnetic, are considered. It is found that the ferromagnetic spin arrangement is the most stable spin order at the ground state, regardless of the incorporation of spin–orbit coupling. The density of states and band structure plots are used to validate the obtained ground state structure, which is further validated by the Bader charge analysis and the charge density distribution of the individual atoms. The obtained results of magnetocrystalline anisotropy energy, total magnetic moment, Curie temperature, and the spin-polarization hint at the possible application of this compound in spintronics devices such as bit-patterned media.

Symmetry-Breaking Effects of Near-Infrared II Thermoplasmonics of Gold–Silica–Cuprous Selenide Hybrid Nanoshells

This study presents a numerical investigation of the plasmonic and photothermal properties of Au-silica-Cu2–xSe hybrid nanoshells (Cu2–xSe HNSs) consisting of a silica-Cu2–xSe core–shell nanoshell embedded with a spherical Au core at varied core offsets. The plasmon modes in the symmetry-broken Cu2–xSe HNSs are explained by plasmon hybridization theory in combination with charge density distribution. Results unveil that the hybridized plasmon modes in a symmetry-broken Cu2–xSe HNS arise from the interaction of the primitive plasmon modes of the same angular momentum on the Au core and the Cu2–xSe nanoshell. An increase in the core offset redshifts and weakens the near-infrared II (NIR-II) plasmon band corresponding to the low-energy bonding dipolar mode but redshifts and enhances the low-energy bonding quadrupolar mode. At the NIR-II plasmon resonance wavelengths, the temperature increase distribution is uniform on the Au core but inhomogeneous on the Cu2–xSe nanoshell. The variation of the temperature increase with the core offset suggests spectral tunability of NIR-II thermoplasmonic properties in the Cu2–xSe HNSs through varying the core offset. Our work provides a paradigm for rational design of NIR-II plasmonic materials with optimal photothermal performances for in vivo biomedical applications through symmetry breaking.