Electron Density Hole Research Articles

Enhancement of ionospheric heating effect by chemical release

The ionosphere can be artificially modified by employing ground-based high-power high-frequency electromagnetic waves to irradiate the ionosphere. This modification is achieved through the nonlinear interaction between the electromagnetic waves and the ionospheric plasma, leading to changes in the physical properties and structure of the ionosphere. The degree of artificial modification of the ionosphere is closely related to the heating energy density of high-frequency pump waves. Due to the high density of neutral constituents in the lower ionosphere and the high frequency of electron-neutral collisions, the energy of heating pump waves will be absorbed and attenuated during the penetration of the low ionosphere, seriously affecting the heating effect. This paper proposes a method to reduce the absorption of ionospheric heating pump waves by releasing electron attachment chemicals into low ionosphere to form a large-scale electron density hole. A model for mitigating pump waves absorption based on SF6 release is established, and the absorption at different frequencies is quantitatively calculated. The propagation characteristics of high-frequency signals in ionospheric holes are studied using a three-dimensional ray tracing method, and the results demonstrate that the chemical release method not only reduces the absorption attenuation of heating pump waves but also forms spherical electron density holes, which exhibit a focusing effect on the heating beam and enhance the heating effect. The results are of great significance for understanding the nonlinear interaction between electromagnetic wave and ionospheric plasma and improving the ionospheric heating efficiency.

Experimental Spectroscopic, Quantum Computational, Hirshfeld Surface, Molecular Docking, and Electronic Excitation Studies on an Antibiotic Agent: SDZ

In this report sulfadiazine (SDZ) has been experimentally and quantum chemically investigated. Computational analysis was carried out theoretically using the density functional theory (DFT) approach/B3LYP and 6-311++G(d,p) level to obtain optimized geometrical structure and vibrational modes analysis and other various calculations. A detailed description of the intermolecular interactions of the crystal surface were carried out by means of Hirshfeld surface analysis and fingerprint plots. Exploration of electron excitation from occupied to unoccupied orbitals in a single electron pair occurs, with dimethyl sulfoxide (DMSO) and MeOH as solvents and electron density distribution (EDD) and hole density distribution (HDD) maps were drawn in an excited state. The molecule reactivity region MEP, molecular stability, natural bond orbital (NBO), HOMO–LUMO, dipole moment (μ), polarizability (α), and hyperpolarizability (β) nonlinear optical (NLO), have all been taken into account. NBO analysis was carried out and the hybridization of atoms that form bonds was evaluated. The charge transfer of the title molecule has been examined by TD-DFT method The UV–Vis spectrum was obtained by employing the TDDFT/PCM method and compared with experimental spectra. Calculated HOMO→LUMO energy gap and charge transfer in the molecule was investigated. Chemical descriptors indicate the reactivity of the molecule as a whole, and Fukui function calculations were used to examine the reactive locations of the compound. The electrophilicity index was calculated and the bio-activity of the molecule was studied. However, biological research like drug-likeness and molecular docking are also done on the molecule.

Methyl groups as widespread Lewis bases in noncovalent interactions

It is well known that, under certain conditions, C(sp3) atoms behave, via their σ-hole, as Lewis acids in tetrel bonding. Here, we show that methyl groups, when bound to atoms less electronegative than carbon, can counterintuitively participate in noncovalent interactions as electron density donors. Thousands of experimental structures are found in which methyl groups behave as Lewis bases to establish alkaline, alkaline earth, triel, tetrel, pnictogen, chalcogen and halogen bonds. Theoretical calculations confirm the high directionality and significant strength of the interactions that arise from a common pattern based on the electron density holes model. Moreover, despite the absence of lone pairs, methyl groups are able to transfer charge from σ bonding orbitals into empty orbitals of the electrophile to reinforce the attractive interaction.

Significant bonding rearrangements triggered by Mg4 clusters.

The structure, stability, and bonding of the complexes formed by the interaction of Mg4 clusters and first row Lewis bases, namely, ammonia, water, and hydrogen fluoride, have been investigated through the use of high-level G4 single-reference and CASPT2 multireference formalisms. The adducts formed reflect the high electrophilicity of the Mg4 cluster through electron density holes in the neighborhood of each metallic center. After the adduct formation, the metallic bonding of the Mg4 moiety is not significantly altered so that the hydrogen shifts from the Lewis base toward the Mg atoms lead to new local minima with enhanced stability. For the particular case of ammonia and water, the global minima obtained when all the hydrogens of the Lewis base are shifted to the Mg4 moiety have in common a very stable scaffold with a N or an O center covalently tetracoordinated to the four Mg atoms, so the initial bonding arrangements of both reactants have completely disappeared. The reactivity features exhibited by these Mg4 clusters suggest that nanostructures of this metal might have an interesting catalytic behavior.

Temporal 3D refined simulation of SF6 release in the ionosphere

A number of significantstudies have been dedicated to SF6 releases. However, given the complicated nature, the simulations provided at the design phases are still not consistent with those diagnosed in experiments. It is mainly because the actual conditions of experiments have not been fully introduced in the state-of-art models. A temporal 3D refined simulation model of SF6 release by a rocket payload is proposed in this paper. It first considers the release status (rocket attitude, velocity, etc.), release process (duration, injection velocity, the flux of the chemical release, etc.) and ambient neutral wind. This model is better than existing ones; the latter can only deal with release from a point source. The time-dependent drift of the released cloud, driven by the velocities of the rocket inertia and neutral wind, are calculated accurately. The non-uniform spherical structure of the electron density hole driven by the lasting release along the trajectory and the injection velocity are also described. The release flow field is calculated by using a new microcell method. The temporal 3D refined model proposed could be useful for improving the diagnosis and also helpful for the theory on chemical releases.

Halogen Bonding from Dispersion-Corrected Density-Functional Theory: The Role of Delocalization Error.

Halogen bonds are formed when a Lewis base interacts with a halogen atom in a different molecule, which acts as an electron acceptor. Due to its charge transfer component, halogen bonding is difficult to model using many common density-functional approximations because they spuriously overstabilize halogen-bonded dimers. It has been suggested that dispersion-corrected density functionals are inadequate to describe halogen bonding. In this work, we show that the exchange-hole dipole moment (XDM) dispersion correction coupled with functionals that minimize delocalization error (for instance, BH&HLYP, but also other half-and-half functionals) accurately model halogen-bonded interactions, with average errors similar to other noncovalent dimers with less charge-transfer effects. The performance of XDM is evaluated for three previously proposed benchmarks (XB18 and XB51 by Kozuch and Martin, and the set proposed by Bauzá et al.) spanning a range of binding energies up to ∼50 kcal/mol. The good performance of BH&HLYP-XDM is comparable to M06-2X, and extends to the "extreme" cases in the Bauzá set. This set contains anionic electron donors where charge transfer occurs even at infinite separation, as well as other charge transfer dimers belonging to the pnictogen and chalcogen bonding classes. We also show that functional delocalization error results in an overly delocalized electron density and exact-exchange hole. We propose intermolecular Bader delocalization indices as an indicator of both the donor-acceptor character of an intermolecular interaction and the delocalization error coming from the underlying functional.

X-ray Crystallographic Structure of 3-(Propan-2-ylidene) benzofuran-2(3H)-one

3-(Propan-2-ylidene)benzofuran-2(3H)-one, C11H10O2, crystallizes in the monoclinic space group P21/c with unit cell parametersa =7.1869(3), b = 18.0636(10), c = 13.1656(7) b= 96.763(3), V =1697.28(15) , Z = 8 (Z? = 2 independent molecules, A and B, per asymmetric unit), Dc = 1.363 g cm-3 and the linear absorption coefficient = 0.093 mm-1. The crystal structure determination was carried out using MoKa X-ray data measured at 120(2) K. In the final refinement cycle the data/restraints/parameter ratios were 3827/0/239, the goodness-of-fit on F2 = 1.019. Final R indices for [I>2sigma(I)] were R1 = 0.0517, wR2 = 0.1115 and R indices (all data) R1 = 0.1007, wR2 = 0.1354. The largest electron density difference peak and hole were 0.254 and -0.244 electrons sup>-3, respectively. The two independent molecules A and B have essentially identical bond lengths and angles and are highly planar, with rms deviation for all 12 non-H atoms of 0.0292 for molecule A and 0.0592 for molecule B. The two molecules in the asymmetric unit are assembled parallel to each other within 1.58(4) with each of the six atoms of benzene ring A overlapping with one of the atoms in benzene ring B at a mean distance of 3.84(3) . The closest contacts between molecules A and B are C(12A)H---O(4B) = 3.521 and C(11B)H---O(4A) = 3.441 The crystal structure is formed by infinite sheets of these assemblies all lying parallel to the (1 0`1) plane. The presence of two independent molecules in the asymmetric unit provides an opportunity to examine the molecular geometry in detail by comparison. The benzene ring in both molecules A and B exhibits distortions as a result of the presence of the furan moiety. In particular, C(1)-C(6) = 1.369(2) in molecule A and 1.367(2) in molecule B are both significantly less than the average of the other 10 C-C bonds, 1.393(2), by about 12?. Other examples of crystal structures are discussed where this effect is observed.

Scaling method for the pair-density-functional theory in combination with energy functionals satisfying the virial theorem: Checking the validity via atomic-structure calculations

We perform atomic-structure calculations for the neutral Ne, Mg, and Ar atoms on the basis of the recently proposed correction method (scaling method) for the pair-density (PD) -functional theory [Phys. Rev. A 84, 044502 (2011)]. The formal features of the scaling method are that the search region of PDs is substantially extended and that the resultant variationally best PD, which can be obtained without the heavy calculation tasks, satisfies the virial theorem rigorously. To enjoy the benefit of these features, we also develop the approximate form of the kinetic energy functional. It is shown by the atomic-structure calculations that the scaling method can improve well not only various energy functionals but also the spatial profiles of the electron density and exchange-correlation hole. Especially it is found that the scaling method makes preferential modifications to the energetically effective regions of the electron density and exchange-correlation hole. These results suggest that the scaling method efficiently puts the PD close to the correct ground-state PD.

Dibenzo[b,g]indeno[1′,2′:3,4]fluoreno[1,2-d]oxonine-5,11,16,21-tetraone

The asymmetric unit of the title compound, C34H16O5, contains two independent mol­ecules (A and B) with similar conformations. The two benzene rings attached to the nine-membered ring are inclined to one another at 63.62 (14)° in mol­ecule A and 68.23 (12)° in mol­ecule B. One intra­moleculer C—H⋯O hydrogen bond occurs in mol­ecule A and two are observed in mol­ecule B. In the crystal, mol­ecules are linked by weak C—H⋯O hydrogen bonds, forming a three-dimensional network structure with R 2 2(10) and R 2 2(24) ring motifs. Aromatic π–π stacking interactions [centroid–centroid distances = 3.7572 (19), 3.6996 (19) and 3.7043 (19) Å] are also observed. The unit cell contains a pair of voids of 37 (2) Å3 about an inversion centre but the residual electron density (highest peak = 0.19 e Å−3 and deepest hole = −0.20 e Å−3) in the difference Fourier map suggests that no solvent mol­ecule occupies this void.

Arbitrary amplitude Langmuir solitons in a relativistic electron–positron plasma

AbstractThe arbitrary amplitude Langmuir solitons are investigated in an unmagnetized, warm, relativistic plasma, consisting of electrons and positrons. Both the species are considered to have equal non-relativistic temperatures, but can have arbitrary relativistic drift speeds, and their dynamics are governed by fluid equations. Using the Sagdeev psuedo-potential approach, the effects of drift speed, Mach number, and thermal temperature on the amplitude and width of the Langmuir solitons are investigated. For the parameters considered, only rarefactive solitons are found. These solitons represent dip in electron density or electron holes in the configuration space. Existence domain of the Langmuir solitons is limited by the minimum and maximum Mach numbers for given parameters. An increase in the electron (positron) temperature leads to an increase in the Langmuir soliton amplitude and their half-widths. On the other hand, increasing the electron (positron) drift speeds results in decreasing soliton amplitudes and their half-widths. For some typical parameters corresponding to the pulsar magnetosphere, namely electron density ~106 cm−3 and electron thermal velocity of one-tenth of the velocity of light, the electric field of the Langmuir solitons can be of the order of (3–24)kV/m. The presence of such large amplitude electrostatic solitary structures may accelerate electrons and positrons and also produce fine structures of (1–5) microseconds in pulsar radio emissions.

X-Ray Crystallographic Structure of the Cyclic Di-amino Acid Peptide: N,N′-Diacetyl-cyclo(Gly-Gly)

The cyclic di-amino acid peptide N,N′-diacetyl-cyclo(Gly-Gly), C8H10N2O4, crystallizes in the triclinic space group $$ P\bar{1} $$ with unit cell parameters a = 9.4855(4) A, b = 10.0250(3) A, c = 10.0763(4) A, α = 73.682(2)°, β = 82.816(2)°, γ = 81.733(2)°, V = 906.40(6) A3, Z = 4 (2 molecules, A and B, per asymmetric unit), Dc = 1.452 g cm−3 and linear absorption coefficient 0.118 mm−1. The crystal structure determination was carried out with MoKα X-ray data measured at 120(2) K. In the final refinement cycle the data/restraints/parameter ratios were 4124/0/258 and goodness-of-fit on F2 = 1.0008. Final R indices for [I > 2σ(I)] were R1 = 0.0501, wR2 = 0.1007 and R indices (all data) R1 = 0.0864, wR2 = 0.11180. The largest electron density difference peak and hole were 0.241 and −0.232 e A−3, respectively. The DKP rings in both molecules A and B have boat conformations with pseudo mm2 (C2v) symmetry if the N atoms and CH2 groups are considered identical. In each case, the prow and stern of the boat are the α-carbons C(3) and C(6). The overall molecular symmetry of molecules A and B is approximately C2 with the twofold symmetry axis of the DKP boat being maintained through the centre of the DKP ring. Details of the molecular geometry are compared with that of the parent compound cyclo(Gly-Gly) in which the DKP ring is planar with exact symmetry $$ \bar{1} $$ (Ci). The crystal structure of the cyclic di-amino acid peptide N,N′-diacetyl-cyclo(Gly-Gly) at 120 K is presented. There are two independent molecules A and B per asymmetric unit. The DKP rings in both molecules exhibit the same boat conformation with approximate mm2 (C2v) symmetry, ignoring differences between the N atoms and CH2 groups. Both molecules have approximate overall twofold (C2) symmetry.

X-Ray Crystallographic Structure and Absolute Configuration of the Cyclic Di-amino Acid Peptide: Cyclo(l-HomoCySH-l-HomoCySH)

The cyclic di-amino acid peptide cyclo(l-homoCySH-l-homoCySH) [(3S, 6S)-3, 6-bis(2-sulfanylethyl) piperazine-2,5-dione, C8H14N2O2S2, crystallizes in the orthorhombic space group P212121 with unit cell parameters a = 6.1509(2) A, b = 18.0217(9) A, c = 29.6166(14) A, V = 3283.0(2) A3, Z = 12 (3 molecules, A, B and C, per asymmetric unit), D c = 1.422 g cm−3 and a linear absorption coefficient of 0.464 mm−1. The crystal structure determination was carried out with MoKα X-ray data measured at 120(2) K. In the final refinement cycle the data/restraints/parameter ratios were 5595/0/385 and goodness-of-fit on F 2 = 1.084. Final R indices for [I > 2sigma(I)] were R1 = 0.0746, wR2 = 0.1356 and R indices (all data) R1 = 0.1092, wR2 = 0.1529. The largest electron density difference peak and hole were 0.526 and −0.445e A−3. The DKP rings in all three molecules are essentially, and unusually, planar and the C=O oxygen atoms are co-planar with the ring in each case. Ring atom rms deviations, including the =O groups, are 0.0668, 0.0658 and 0.0656 A in molecules A, B and C, respectively. Details of the molecular geometry are compared with the compound cyclo(Gly-Gly) (Degeilh R, Marsh RE Acta Cryst 12:1007, 1959) and in addition some cyclic di-amino acid peptides in which the DKP rings have more puckered boat conformations. The crystal structure of the cyclic di-amino acid peptide: cyclo(l-homoCySH-l-homoCySH) at 120 K is presented. There are three independent molecules A, B and C, per asymmetric unit in space group P212121 which is a rare occurrence. The DKP rings in all three molecules, with the exception of the H atoms, are essentially, and unusually, planar and the C=O oxygen atoms are co-planar with the ring in each case. Ring atom rms deviations, including the =O groups, are 0.0668, 0.0658 and 0.0656 A in molecules A, B and C, respectively.

Recent developments in quantum plasma physics

We present a review of recent developments in nonlinear quantum plasma physics involving quantum hydrodynamics and effective nonlinear Schrödinger equation formalisms, for describing collective phenomena in dense quantum plasmas with degenerate electrons. As examples, we discuss simulation studies of the formation and dynamics of dark solitons and quantum vortices, and of nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) in dense quantum-electron plasmas with immobile ions. The electron dynamics of dark solitons and quantum vortices is governed by a pair of equations comprising the nonlinear Schrödinger and Poisson system of equations. Both dark solitons and singly charged electron vortices are robust, and the latter tend to form pairs of oppositely charged vortices. The two-dimensional quantum-electron vortex pairs survive during collisions under the change of partners. The dynamics of the CPEM waves is governed by a nonlinear Schrödinger equation, which is nonlinearly coupled with the Schrödinger equation of the EPOs via the relativistic ponderomotive force, the relativistic electron mass increase in the CPEM field, and the electron density fluctuations. The present governing equations in one-spatial dimension admit stationary solutions in the form of dark solitons. The nonlinear equations also depict trapping of localized CPEM wave envelopes in the electron density holes that are associated with a positive potential profile.

Low Temperature Crystal Structure of N-Acetyl-l-Glutamic Acid: Comparison with the DFT Calculated Structure

N-acetyl-l-glutamic acid, crystallizes in the orthorhombic space group P212121 with unit cell parameters a = 4.747(3), b = 12.852(7), c = 13.906(7) A, V = 848.5(8) A3, Z = 4, density (calculated) = 1.481 mg/m3, linear absorption coefficient 0.127 mm−1. The crystal structure determination was carried out with MoKα X-ray data measured with liquid nitrogen cooling at 100(2) K temperature. In the final refinement cycle the data/restraints/parameter ratios were 1,691/0/131; goodness-of-fit on F2 = 1.122. Final R indices for [I > 2sigma(I)] were R1 = 0.0430, wR2 = 0.0878 and R indices (all data) R1 = 0.0473, wR2 = 0.0894. The largest electron density difference peak and hole were 0.207 and −0.154 eA−3. Details of the molecular geometry are discussed and compared with a model DFT structure calculated using Gaussian 98. The low temperature X-ray structure of N-acetyl-l-glutamic acid, including absolute configuration, is described. Comparison with the DFT structure is also discussed. Molecular conformation of N-acetyl-l-glutamic acid: (a) drawn with MERCURY [22] and (b) surfaces drawn with VMD [26].

Electron density hole and quadruple structure of B y during collisionless magnetic reconnection

In collisionless reconnection, the magnetic field near the separatrix is stronger than that around the X-line, so an electron-beam can be formed and flows toward the X-line, which leads to a decrease of the electron density near the separatrix. Having been accelerated around the X-line, the electrons flow out along the magnetic field lines in the inner side of the separatrix. A quadruple structure of the Hall magnetic field By is formed by such a current system. A 2D particle-in-cell (PIC) simulation code is used in this paper to study the collisionless magnetic reconnection without an initial guide field. The current system described above is proved by the simulations. Furthermore, the position of the peak of the Hall magnetic field By is found to be between the separatrix and the center of the current sheet, which is verified by Cluster observations.

Nonlinear Aspects of Quantum Plasma Physics: Nanoplasmonics and Nanostructures in Dense Plasmas

We present a short review of recent developments in nonlinear quantum plasma physics, including quantum hydrodynamic and effective nonlinear shrödinger equation formalisms, for describing collective phenomena in quantum plasmas. As examples we discuss simulation studies of the formation and dynamics of dark solitons and vortices, and of nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) in dense in quantum electron plasmas. The electron dynamics of dark solitons and vortices is governed by a pair of equations comprising the nonlinear Schrödinger and Poisson equations. Both dark solitons and singly charged electron vortices are robust, and the latter tend to form pairs of oppositely charged vortices. The two-dimensional quantum electron vortex pairs survive during collisions under the change of partners. The dynamics of the CPEM waves is governed by a nonlinear Schrödinger equation, which is nonlinearly coupled with the Schrödinger equation of the EPOs via the relativistic ponderomotive force, the relativistic electron mass increase in the CPEM field, and the electron density fluctuations. The present governing equations in one spatial dimension admit stationary solutions in the form dark envelope solitons. The nonlinear equations admit the modulational instability of an intense CPEM pump wave against EPOs, leading to the formation and trapping of localized CPEM wave envelopes in the electron density holes that are associated with positive potential profiles.

Localized plasmons in quantum plasmas

We consider the nonlinear interactions between finite amplitude electron and ion plasma oscillations in a fermionic quantum plasma. Accounting for the quantum statistical electron pressure and the quantum Bohm potential, we derive a set of coupled nonlinear equations that govern the dynamics of modulated electron plasma oscillations (EPOs) in the presence of the nonlinear ion oscillations (NLIOs). We numerically study stationary solutions of our coupled nonlinear equations. We find that the quantum parameter H (equal to the ratio between the plasmonic and electron Fermi energy densities) introduces new features to the electron density and electric potential humps of localized NLIOs in the absence of EPOs. Furthermore, the nonlinear coupling between the EPOs and NLIOs gives rise to a new class of envelope solitons composed of bell shaped electric field envelope of the EPOs, which are trapped in the electron density hole (and an associated negative oscillatory electric potential) that is produced by the ponderomotive force of the EPOs. The knowledge of the localized plasmonic structures is of immense value for interpreting experimental observations in dense quantum plasmas.

Nonlinear Interactions between Electromagnetic Waves and Electron Plasma Oscillations in Quantum Plasmas

We consider nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) in a dense quantum plasma, taking into account the electron density response in the presence of the relativistic ponderomotive force and mass increase in the CPEM wave fields. The dynamics of the CPEM waves and EPOs is governed by the two coupled nonlinear Schrödinger equations and Poisson's equation. The nonlinear equations admit the modulational instability of an intense CPEM pump wave against EPOs, leading to the formation and trapping of localized CPEM wave pipes in the electron density hole that is associated with a positive potential distribution in our dense plasma. The relevance of our investigation to the next generation intense laser-solid density plasma interaction experiments is discussed.

Electrostatic coherent structures generation by local heating in a collisionless plasma

Abstract We propose a new mechanism for the generation of electrostatic coherent structures and Langmuir fluctuations in a stratified plasma. The model is base on open boundary 1D Vlasov simulations where heated electrons are injected by applying a temporal continuous periodic modification of the width of the electron distribution function at one boundary of the simulation box. To our knowledge, that is the first time that a “localized heating” mechanism is studied as a driver for the development of bi(multi)polar electric field with their associated electron density holes and vortices in the phase space. After the development of many electrostatic coherent structures, the injected fast particles are free to move along their ballistic limit, while electrons moving at nearly, or less than, the thermal speed are diffused in phase space by the local fields.

Electron-Acoustic Compressive Soliton and Electron DensityHole in Aurora

Electron-acoustic solitary waves have been studied in an electron-beamplasma system. It is found that the solution of compressive soliton onlyexists within a limited range of soliton velocity around the electronbeam velocity. A compressive electron-acoustic soliton alwaysaccompanies with a cold electron density hole. This theoretical model isused to explain the `fast solitary wave' event observed by the FASTsatellite in the mid-altitude auroral zone.