Electron Density Distribution Research Articles

Modulating inner Helmholtz layer by electrocatalytically sieving [Zn(H2O)6]2+ for 10000-cycle zinc-ion hybrid capacitors under extremely harsh conditions

Zinc-ion hybrid capacitors (ZIHCs) are famous for potential applications in grid-scale energy storage devices with fast-charge capability. However, their industrialization is severely plagued by inferior performance caused by the sluggish Zn2+ desolvation kinetics with large spatial diffusion hinderance of [Zn(H2O)6]2+ in the inner Helmholtz plane (IHP) layer, especially under low-temperature surroundings. Herein, the simultaneous rapid desolvation strategy via pore sieving and electrocatalysis is initially proposed to promote [Zn(H2O)6]2+ dissociation, regulating the isolated Zn2+ behaviors in the IHP. Specifically, heteroatom-decorated carbon microspheres with multi-level channels modulate the local distribution of electronic density, generating abundant catalytic sites to drive the kinetics of [Zn(H2O)6]2+ desolvation and free Zn2+ diffusion. Impressively, the catalytic desolvation behaviors and storage mechanism of ZIHCs are comprehensively investigated using in-situ electrochemical quartz crystal microbalance and various ex-situ/in-situ measurements as well as theoretical simulations, revealing significant interactions of isolated Zn2+ in the IHP. Consequently, the assembled ZIHCs exhibit a superior capacity of 177.2 mAh g−1, corresponding to a high energy density of 158.8 Wh kg−1, and provide a power density as high as 15.7 kW kg−1. Exposed to extreme environment, the ZIHCs encountered with severe solvation structure stabilize for 10000 cycles withcapacity retention of 99.42%, providing new insights of catalytically sieving into modulating IHP for high-performance ZIHCs under extreme conditions.

Topological indices & Hirshfeld pseudo-surfaces synergy to understand the radiation attenuation in materials: Case of study spinel mineral crystals

The present work deals with the radiation attenuation characteristics of spinel minerals, a unique class of minerals with diverse crystalline structures and chemical compositions. We analyze the MAC and LAC in various photon energy spectrum using XCOM and Phys-X software tools. In addition to traditional methods, we employ topological indices (TIs) and Hirshfeld pseudo-surfaces (HPSs) to explore the atomic interactions and electron density distributions within these minerals to pinpointed their effects on the on these γ-radiation attenuation coefficients. Our findings reveal that MAC values decrease with increasing photon energy, a trend observed across all studied spinel minerals. The use of the HPSs provides visual insights into electron density distributions and intermolecular interactions mastered by 2D fingerprints which are correlated with the γ-attenuation of these spinels crystal. Linear regression correlations between TIs and MAC, LAC values demonstrate strong relationships, with the first Zagreb coindex and the Forgotten Index (F-index) emerging as reliable predictors of γ-rays radiations shield properties.

Elucidation of Design Criteria for V-based Redox Mediators: Structure-Function Relationships that Dictate Rates of Heterogeneous Electron Transfer.

Redox mediators are attractive solutions for addressing the stringent kinetic stipulations required for efficient energy conversion processes. In this work, we compare the electrochemical properties of four vanadium complexes, namely [V(acac)3], [V6O7(OMe)12], [nBu4N]3[V6O13(TRISNO2)2], and [nBu4N]5[V18O46(NO3)] in non-aqueous solutions on glassy carbon electrodes. The goal of this study is to investigate the electron transfer kinetics and diffusivity of these compounds under identical experimental conditions to develop an understanding of structure-function relationships that dictate the physicochemical properties of vanadium oxide assemblies. Complex selection was dictated by two criteria - (1) nuclearity of the transition metal complexes (2) distribution of electron density in the native electronic configuration. Our analyses establish that electronic communication between metal centers significantly impacts charge transfer kinetics of these vanadium-based compounds.

Direct Observation of Polaritonic Chemistry by Nuclear Magnetic Resonance Spectroscopy

AbstractPolaritonic chemistry is emerging as a powerful approach to modifying the properties and reactivity of molecules and materials. However, probing how the electronics and dynamics of molecular systems change under strong coupling has been challenging due to the narrow range of spectroscopic techniques that can be applied in situ. Here we develop microfluidic optical cavities for vibrational strong coupling (VSC) that are compatible with nuclear magnetic resonance (NMR) spectroscopy using standard liquid NMR tubes. VSC is shown to influence the equilibrium between two conformations of a molecular balance sensitive to London dispersion forces, revealing an apparent change in the equilibrium constant under VSC. In all compounds studied, VSC does not induce detectable changes in chemical shifts, J‐couplings, or spin‐lattice relaxation times. This unexpected finding indicates that VSC does not substantially affect molecular electron density distributions, and in turn has profound implications for the possible mechanisms at play in polaritonic chemistry under VSC and suggests that the emergence of collective behavior is critical.

Direct Observation of Polaritonic Chemistry by Nuclear Magnetic Resonance Spectroscopy.

Polaritonic chemistry is emerging as a powerful approach to modifying the properties and reactivity of molecules and materials. However, probing how the electronics and dynamics of molecular systems change under strong coupling has been challenging due to the narrow range of spectroscopic techniques that can be applied in situ. Here we develop microfluidic optical cavities for vibrational strong coupling (VSC) that are compatible with nuclear magnetic resonance (NMR) spectroscopy using standard liquid NMR tubes. VSC is shown to influence the equilibrium between two conformations of a molecular balance sensitive to London dispersion forces, revealing an apparent change in the equilibrium constant under VSC. In all compounds studied, VSC does not induce detectable changes in chemical shifts, J-couplings, or spin-lattice relaxation times. This unexpected finding indicates that VSC does not substantially affect molecular electron density distributions, and in turn has profound implications for the possible mechanisms at play in polaritonic chemistry under VSC and suggests that the emergence of collective behavior is critical.

First numerical evidence of the two-close frequency heating effect on electron cyclotron resonance ion sources

The two-close frequency heating (TCFH) is a new implementation of the well-known two frequency heating. In TCFH, the two frequencies differ around 200-300 MHz each other in order to establish two contiguous ECR resonance zones. TCFH has been proved to be a powerful technique to suppress plasma instabilities in Electron Cyclotron Resonance Ion Sources (ECRIS), as well as to improve their performances. Its beneficial effect, compared to the application of a single frequency, is always deduced from the extracted charge states distributions and from the detection of the plasma self-emission in the X-ray and microwave ranges. This paper presents the first approach to a numerical description of the two-close frequency effect, based on the relevant plasma parameters of the ECRIS setup operating at ATOMKI-Debrecen. Simulations have been performed by our PIC-Full Wave code, joining electron kinetics and FEM solution of Maxwell equations in a cold plasma model. Results on plasma electron density and energy distribution will be shown, together with a direct comparison with the already published data on X ray emission.

Ferrocene Appended D-π-A chromophores for Dye-Sensitized Solar Cells: Synthesis, Photophysical, Effect of Co-adsorbent on Photovoltaic Efficiencies and DFT studies

A new ferrocene conjugated donor–π–acceptor type of dyes 1 and 2 were synthesized and characterized using different spectroscopic techniques (FT-IR, NMR, and ESI-mass). The intramolecular charge transfer process of both the dyes were analysed using the solvatochromic method, which reveals positive solvatochromism due to its well stabilization in the excited states than in the ground states. The electrochemical behavior of the dyes 1 and 2 were carried out by the cyclic voltammetric technique, which shows quasi-reversible in nature, and the potentials were further utilized for the band gap calculation with UV–visible data [2.99 eV (1) and 2.88 eV (2)]. The photovoltaic attainments of the dyes 1 and 2 were studied through the dye-sensitized solar cells (DSSCs) in the presence and absence of co-adsorbent like chenodeoxycholic acid (CDCA), which act as an anti-dye aggregation material. The photovoltaic parameters like short circuit current density (Jsc) = 0.067 mA cm2, open circuit voltage (Voc) = 0.444 V, fill factor (FF) = 0.447, and the cell displayed an overall conversion efficiency of 0.013 % for dye 2. In contrast, the power conversion efficiency (PCE) was found to be enhanced to 0.177 % (Jsc = 0.389 mA/cm2, Voc = 0.577 V, FF =0.790), in the presence of chenodeoxycholic acid (CDCA) co-adsorbent. This enhancement in efficiency is due to reduced dye aggregation and increased electron injection in the presence of CDCA. In addition, chromophore 2 has 1.4 times higher efficiencies than 1, attributing to the presence of an additional phenyl group making an efficient intramolecular process of 2. Furthermore, the incident photon to current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) studies reveal the dye efficiencies were directly proportional to that of the power conversion efficiency (PCE), respectively. Moreover, the electronic structure and electron density distribution analysis were analysed for both dyes 1 and 2 to confirm the intramolecular charge transfer properties using density-functional theory (DFT) and time-dependent density-functional theory (TD-DFT) calculations using the B3LYP/ 6–31+G** level of theory.

D-region ionospheric disturbances due to the December 2019 solar eclipse observed using multi-station VLF radio network

We present the low-latitude D-region (60–90 km) ionospheric disturbances due to the December 2019 annular solar eclipse observed using the multi-station Very Low Frequency (VLF) radio network in West Bengal, India. VLF signals from communication transmitters were received from ten places using low-cost VLF radio receivers. The receivers were capable of recording the amplitudes of VLF signals mainly from the transmitters VTX, India at 18.2 kHz and NWC, Australia at 19.8 kHz. During the solar eclipse, the VTX signal experienced considerable positive, negative, and mixed-type amplitude variations depending on the propagation lengths between the transmitter and receivers, whereas the NWC signal displayed a relatively small amplitude response. We have also found that the highest VLF signal disturbances in each propagation path occurred after the time when the solar obscuration was maximum over the entire path. We used the observations of the VTX signal to formulate the relationship between solar obscuration and D-region electron density reduction during the solar eclipse. On the basis of this, we presented the electron density distribution of the D-region ionosphere during the solar eclipse across the Indian subcontinent. This study shows a useful method for integrating VLF observations and simulations to estimate the D-region electron density distribution over a vast area during a solar eclipse.

Efficient computational modeling of electronic stopping power of organic polymers for proton therapy optimization

This comprehensive study delves into the intricate interplay between protons and organic polymers, offering insights into proton therapy in cancer treatment. Focusing on the influence of the spatial electron density distribution on stopping power estimates, we employed real-time time-dependent density functional theory coupled with the Penn method. Surprisingly, the assumption of electron density homogeneity in polymers is fundamentally flawed, resulting in an overestimation of stopping power values at energies below 2 MeV. Moreover, the Bragg rule application in specific compounds exhibited significant deviations from experimental data around the stopping maximum, challenging established norms.

Understanding Ionospheric and Geomagnetic Effects on Residual Biases in Radio Occultation Data for Stratospheric Climate Monitoring

AbstractHigher‐order residual ionospheric errors in Global Navigation Satellite System (GNSS) radio occultation (RO) data can induce a systematic residual ionospheric bias (RIB) in RO bending angles, which can impact stratospheric climate monitoring. The main RIB causes are the ray path splitting of dual‐frequency GNSS signals, the electron density distribution along the ray path and at the RO receiver location, and the geomagnetic field. In this study, we investigate the ionospheric and geomagnetic effects on RO‐retrieved stratospheric bending angle and temperature profiles by inspecting the kappa and bi‐local RIB correction methods, the current state‐of‐the‐art methods, using multiple RO satellite mission data in different ionospheric and geomagnetic conditions. We find that, globally, the layer mean/median RIBs of the kappa and bi‐local correction methods exhibit similar behaviors for different RO missions: the estimated bending angle RIBs reach about −0.025/−0.01 and −0.024/−0.008 μrad in the upper (40–45 km) and lower (30–35 km) stratosphere, respectively, while the temperature RIBs reach about −1.0/−0.3 and −0.2/−0.1 K in these layers. However, in the equatorial day time region, the RIB statistics of the mission results diverge. Both the kappa and bi‐local RIBs increase in magnitude with increasing ionization and geomagnetic field strength but show no increase with an increasing degree of ionospheric asymmetry. Overall, the more refined bi‐local method has higher capacity than the comparatively simple kappa method to represent the variability of the ionospheric and geomagnetic conditions that affect RO events. This is important for regional‐scale studies, where the geomagnetic term can be of key relevance.

Fragmentation and charge transfer in cyclic dipeptides with an aromatic side chain induced by VUV radiation

The fragmentation of three cyclic dipeptides (c-Glycil-Phenylalanine, c-Tryptophan-Tyrosine and c-Tryptophan-Tryptophan), characterized by an aromatic side chain, has been investigated by synchrotron radiation and photoelectron-photoion coincidence (PEPICO) experiments, assisted by atomistic simulations. The PEPICO experiments show that the charged moiety containing the aromatic side chain is the main fragment in the three samples. The theoretical exploration of the potential energy surfaces has allowed to identify the possible fragmentation paths leading to the formation of these fragments. Then, the analysis of the differences in the electronic density distributions of the neutral molecule and the cation and a molecular dynamics simulation provided an understanding of the preferred localization of the positive charge on the aromatic side chain of the cyclic dipeptide.

Parametric characterization of arcs in semi-sealed splitter plate DC circuit breakers

Precisely assessing plasma parameters holds paramount importance in investigating the arc extinguishing mechanism of semi-sealed splitter plate DC circuit breakers, refining the configuration of splitter plates, and optimizing the overall structural design of circuit breakers. Based on the principle of the Langmuir probe, a double probe diagnostic method is proposed to investigate the air arc plasma in the opening process of a DC circuit breaker. The diagnostic circuit of the probes is designed, and three sets of double probes are arranged to trace the evolution of the plasma density during the opening process. The research reveals that the plasma center density, measured by the diagnostic system during the opening process of the DC circuit breaker, is about 1022 m−3–1023 m−3. This density is compared with the diagnostic results obtained by other methods, confirming the accuracy of the Langmuir double probe for plasma measurements in the DC circuit breaker. The study also revealed an exponential decay behavior of electron density along the radial direction of the arc. A mathematical model was employed to describe this phenomenon, establishing a relationship between the distribution of electron density and arc current.

Electron density changes accompanying high-pressure phase transition in AlOOH

Abstract An attempt to compare and describe the differences in the electron density distribution between two phase structures of AlOOH has been made. High-resolution, high-pressure experiments with α-AlOOH diaspore were conducted using single-crystal synchrotron X-ray diffraction data. A multipole model of experimental electron density in the α-AlOOH single crystal was refined. Simultaneously, similar multipole refinement was conducted for another phase of diaspore (δ-AlOOH), this time based on a previously published data set. Both results were compared and supported by density functional theory (DFT) calculations. Although the results are affected by the limited quality of the data, it is clear that the phase transition caused significant changes in the shape and arrangement of the atomic basins. Atomic basins are a much better tool to present subtle electron density distribution changes than traditional polyhedra. Straightforward comparison of datasets available in older scientific papers and current datasets is challenging because of differences in data quality and collection parameters. However, augmenting experimental data with computational results can help reveal important information in even incomplete datasets.

Fingerprints of Chalcogen Bonding Revealed Through 77Se-NMR.

77Se-NMR is used to characterise several chalcogen bonded complexes of derivatives of the organoselenium drug ebselen, exploring a range of electron demand. NMR titration experiments support the intuitive understanding that chalcogen bond donors bearing more electron withdrawing substituents give rise stronger chalcogen bonds. The chemical shift of the selenium nucleus is also shown to move upfield as it participates in a chalcogen bond. Solid-state NMR is used to explore chalcogen bonding in co-crystals. Due to the lack of molecular reorientation on the NMR timescale in the solid state, the shape of the chemical shift tensor can be determined using this technique. A range of co-crystals are shown to have extremely large chemical shift anisotropy, which suggests a strongly anisotropic electron density distribution around the selenium atom. A single crystal NMR experiment was conducted using one of the co-crystals, affording the absolute orientation of the chemical shift tensor within the crystal. This showed that the selenium nucleus is strongly shielded in the direction of the chalcogen bond (due to the approach of the lone pair of the Lewis base), and strongly deshielded in the perpendicular direction. The orientation of the deshielded axis is consistent with the presence of a second σ-hole which is not participating in a chalcogen bond, showing the profound effect of electron density anisotropy on the chemical shift.

Kinetic behavior of secondary electrons in a magnetized voltage-driven discharge using combined rf/dc sources

This study employed particle-in-cell/Monte Carlo simulations, along with test particle methods, to examine the characteristics of secondary electrons (SEs) in a voltage-driven discharge using combined rf/dc sources and operates in the presence of a magnetic field. The behavior of SEs is significantly influenced by the magnetic field, leading to the emergence of complex branches in temporal electron energy probability distributions and spatiotemporal electron density distributions within the sheath. The number of branches is directly correlated to the cyclotron period. Moreover, the application of a direct current (dc) source thickens the sheath at the dc biased electrode while attenuating the sheath on the opposite side. This leads to an asymmetrical modulation of the kinetic behavior of SEs in the two sheaths, ultimately resulting in a substantial increase in electron energy on the side of the dc biased electrode.

A new type of C+⋯Hδ-(C=) bond in adducts of vinyl carbocations with alkenes.

By X-ray diffraction analysis and IR spectroscopy, it was established here that vinyl carbocations C3H5+/C4H7+ with carborane counterion CHB11Cl11- form stable monosolvates C3H5+⋅C3H6/C4H7+⋅C4H8 with molecules of alkenes C3H6/C4H8. They contain molecular group =C+⋯Hδ--Cδ+= with a new type of bond formed by the H atom of the H-C= group of the alkene with the C atom of the C+=C group of the carbocation. The short C+----Cδ+ distance, equal to 2.44 Å, is typical of that of X----X in proton disolvates (L2H+) with an quasi-symmetrical X-H+⋯X moiety (where X = O or N) of basic molecule L. The nature of the discovered bond differs from that of the classic H-bond by an distribution of electron density: the electron-excessive Hδ- atom from the (=)C-H group of the alkene is attached to the C+ atom of the carbocation, on which the positive charge is predominantly concentrated. Therefore, it can be called an inverse hydrogen bond.

Computational insight into the spectroscopic and molecular docking analysis of estrogen receptor with ligand 2,3-dimethyl-N[2-(hydroxy)benzylidene] aniline

A comprehensive approach encompassing a blend of spectral techniques and Density Functional Theory (DFT) was employed to elucidate the electronic, vibrational, structural, and nonlinear optical properties of 2,3-dimethyl-N[2-(Hydroxy)benzylidene] aniline (DNHBA). The investigation of this chemical compound involved a meticulous examination using spectroscopic techniques (FTIR, FT-Raman). The DFT calculations utilized the B3LYP method in conjunction with 6-311G (d, p) basis sets. The findings were substantiated by comparing the estimated vibrational frequencies and molecule geometry with experimental data. Using the Time Dependent −Density Functional Theory (TD-DFT) method to calculate the energy band gap of the compound at different solvents. We looked into frontier molecular orbitals (FMO) Molecular electrostatic potential (MEP) and natural bond analysis (NBO) to determine the compound’s kinetic stability and chemical reactivity. Hirshfeld surface (HS) analysis calculated the O–H..O, H-H and intermolecular interaction energy of the compound. The electron density distribution, interactions, and excitation within the title molecule are illustrated by performing topological analyses (RDG, ELF and LOL) using the Multiwfn software. In addition to these assessments, molecular dynamics provides an understanding of the system's dynamic development over a predefined duration during which atoms and molecules are permitted to interact. Utilizing the molecular docking approach allows us to energize the atomic-level interplay between small molecules and proteins within the binding sites of target proteins. This approach enhances our comprehension of vital biochemical processes associated with the behavior of small molecule. The intricacy and hazards associated with drug discovery and development processes have increased dramatically, leading to higher drug research costs.

Using Three-Dimensional Information to Predict and Interpret the Facial Selectivities of Nucleophilic Additions to Cyclic Ketones.

In this study, we devised a new method to predict facial selectivity by quantifying steric and orbital factors for the nucleophile approaching both π-plane faces. Using this method, we quantified the total electron density and frontier orbital distributions of 163 cyclic ketones with various structures and quantitatively explained the surface selectivity of 323 reactions with eight nucleophiles (BH3, LiAlH4, NaBH4, LiAl(OMe)3H, MeLi, MeMgI, PhLi, and PnMgI). Importance analysis showed a large orbital effect for BH3, LiAlH4, and NaBH4 and the dominance of the steric effect for LiAl(OMe)3H, MeLi, MeMgI, PhLi, and PhMgI. Our method analyzes three-dimensional features based on Gaussian cube files, which can be easily obtained using mainstream computational chemistry software packages, and this approach should prove useful for predicting the rates and facial selectivity of other reactions.

Spatiotemporal reshaping of femtosecond laser pulses on interaction with gas sheath at ionization saturation intensity regime

Interaction of intense ultrashort laser pulse with gases generates a transient spatiotemporal electron density distribution via field ionization, which may lead to the spatiotemporal reshaping of the pulse, viz., its beam profile, pulse width, etc. Here, we present an experimental study on ultrashort laser pulse interaction with argon gas sheath in an ionization saturation intensity regime (∼1015–1017 W/cm2). The present investigation has been performed using a 6 mJ, 1 kHz, and 55−60 fs Ti:Sapphire laser pulse interaction with a ∼2.5 mm long argon sheath. After the laser gas interaction, the laser spatial profile exhibits a multi-ring structure around a central maximum spot. Laser gas interaction parameters, such as laser intensity, gas pressure, etc., affect the ring pattern significantly. Under optimum parameter conditions, the laser pulse has two rings in spatial profile, and the pulse width of the central spot is self-compressed to ∼35 fs. A theoretical calculation reveals that the laser beam’s spatiotemporal profile evolves as it propagates inside the gas sheath. The calculation also demonstrates that the gas ionization profile plays a crucial role in the spatiotemporal reshaping and self-compression of the laser beam. The calculation also shows that the generation of concentric ring patterns in the spatial profile is mainly due to the ionization of argon atoms into Ar+, Ar2+, and Ar3+ species in the interaction region. Such self-compressed laser pulses with concentric ring beam profiles may be useful for high-harmonic generation and shorter attosecond pulse trains.

Halogen Bond-Assisted Supramolecular Dimerization of Pyridinium-Fused 1,2,4-Selenadiazoles via Four-Center Se2N2 Chalcogen Bonding.

The synthesis and structural characterization of α-haloalkyl-substituted pyridinium-fused 1,2,4-selenadiazoles with various counterions is reported herein, demonstrating a strategy for directed supramolecular dimerization in the solid state. The compounds were obtained through a recently discovered 1,3-dipolar cycloaddition reaction between nitriles and bifunctional 2-pyridylselenyl reagents, and their structures were confirmed by the X-ray crystallography. α-Haloalkyl-substituted pyridinium-fused 1,2,4-selenadiazoles exclusively formed supramolecular dimers via four-center Se···N chalcogen bonding, supported by additional halogen bonding involving α-haloalkyl substituents. The introduction of halogens at the α-position of the substituent R in the selenadiazole core proved effective in promoting supramolecular dimerization, which was unaffected by variation of counterions. Additionally, the impact of cocrystallization with a classical halogen bond donor C6F3I3 on the supramolecular assembly was investigated. Non-covalent interactions were studied using density functional theory calculations and topological analysis of the electron density distribution, which indicated that all ChB, XB and HB interactions are purely non-covalent and attractive in nature. This study underscores the potential of halogen and chalcogen bonding in directing the self-assembly of functional supramolecular materials employing 1,2,4-selenadiazoles derived from recently discovered cycloaddition between nitriles and bifunctional 2-pyridylselenyl reagents.