Calculated Electron Density Research Articles

Preparation of BiOCl/Cu2O composite particles and its photocatalytic degradation of moxifloxacin

In this study, BiOCl/Cu2O composite particles were successfully provided by solvothermal method to remove moxifloxacin from water under simulated sunlight radiation, and the influence of BiOCl on the structure and performance of Cu2O was studied. The main degradation intermediate products produced in photocatalysis were analyzed, and the reasons affecting the photocatalytic performance of BiOCl/Cu2O were studied. The reaction site of moxifloxacin was predicted by theoretical calculation. The results show that the prepared samples have high purity and a spherical shape with a particle size of about 3–5 μm. After compounding, the samples have larger specific surface area than pure Cu2O, which increase the absorption of visible light and increase the band gap. The photocurrent response intensity was enhanced, the surface transfer resistance was reduced, and the transfer and separation efficiency of photogenerated electrons and holes was significantly improved. In addition, the photocatalytic performance of the prepared samples was assessed by the decompose of moxifloxacin. The degradation rate of moxifloxacin reached 80.0% in the presence of M2-Cu2O. Finally, it was determined that the main active species in the photocatalytic reaction was ·OH, and based on the nine products analyzed, combined with the calculation of the front-line electron density, the possible degradation path of moxifloxacin was proposed.

Effects of O2 addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges (DBDs) have been widely used in ozone synthesis, materials surface treatment, and plasma medicine for their advantages of uniform discharge and high plasma-chemical reactivity. To improve the reactivity of DBDs, in this work, the O2 is added into Ar nanosecond (ns) pulsed and AC DBDs. The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O2 contents are investigated with optical and electrical diagnosis methods. The DBD uniformity is quantitatively analyzed by gray value standard deviation method. The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n e. The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T e with the ratio of two emission lines. It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time. With the addition of O2, the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O2 −, which promotes the filamentary formation. While, in AC DBD, the added O2 can reduce the intensity of filaments, which enhances the discharge uniformity. The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD. The ratio of Ar emission intensities indicates that the T e drops quickly with the addition of O2 both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T e and n e than AC DBD. The results are helpful for the realization of the reactive and uniform low temperature plasma sources.

Physical and one-dimensional properties of single-crystalline La5AgPb3

We report here the properties of single crystals of La$_{5}$AgPb$_{3}$, which is a member of the $R_5MX_3$ ($R$ = rare earth, $M$ = transition metal or main group element, $X$ = Pb, Sn, Sb, In, Bi) family of chain-like compounds. Measurements of the electrical resistivity, specific heat and magnetic susceptibility are compared to the results of density functional calculations, finding that La$_{5}$AgPb$_{3}$ is a non-magnetic metal with moderate correlations. The analysis of the electrical resistivity and specific heat measurements highlight the importance of lattice vibrations in the material, while the calculated electron density suggests the presence of localized La and well-hybridized Ag atoms that extend along the c-axis in the La$_{5}$AgPb$_{3}$ structure. The temperature dependence of the magnetic susceptibility is consistent with a possible one-dimensional character of La$_{5}$AgPb$_{3}$, where the strength of correlations is much weaker than in one-dimensional conductors that have been previously reported.

Quantum flux densities for electronic-nuclear motion: exact versus Born-Oppenheimer dynamics.

We study the coupled electronic-nuclear dynamics in a model system to compare numerically exact calculations of electronic and nuclear flux densities with those obtained from the Born-Oppenheimer (BO) approximation. Within the adiabatic expansion of the total wave function, we identify the terms which contribute to the flux densities. It is found that only off-diagonal elements that involve the interaction between different electronic states contribute to the electronic flux whereas in the nuclear case the major contribution belongs to the BO electronic state. New flux densities are introduced where in both, the electronic and the nuclear case, the main contribution is contained in the component corresponding to the BO state. As a consequence, they can be determined within the BO approximation, and an excellent agreement with the exact results is found. This article is part of the theme issue 'Chemistry without the Born-Oppenheimer approximation'.

Study of the effects of detection times in laser-induced breakdown spectroscopy and missed variation of plasma parameters with gate width

The time control of signal acquisition in laser-induced breakdown spectroscopy (LIBS) is critical to the quantification of elements in samples. Upon interacting with the laser pulse, the plasma expands and then cools rapidly in tens of microseconds, undergoing temperature variations of over 50,000 K. In the LIBS technique, the signal acquisition is controlled with the delay time, which is the time between the emission of the laser pulse and the reading of the spectrum, and the gate width, which is the integration time of the spectrometer. Although the relationship of the delay time with the measured plasma temperature and electron density is well-known in the literature, little is known about how these parameters vary with different gate widths. Thus, the objective of this work was to evaluate how the measured plasma parameters and the signal-to-noise ratio (SNR) of an atomic line change with different values of delay time and gate width. For this study, two sets of samples were prepared: i) pure NaCl and ii) NaCl with 20 wt% H3BO3, and at concentrations of 1 and 3 wt% Ca. TiO2 and CuSO4 were also added to these samples to facilitate plasma temperature and electron density calculations, which were carried out using a Saha-Boltzmann plot corrected with the one-point calibration method. The results of this study indicated that the measured plasma parameters did not vary with the gate width, even though the SNR of the Ca I line at 643.9 nm increased as the gate width did. Furthermore, the use of the concept of local thermodynamic equilibrium was verified even with long gate widths (≥ 20 μs), except for the 4 μs delay time. Studies with other samples and other combinations of LIBS system parameters, e.g., at sub atmospheric pressure, should be done to confirm and expand these findings.

Accelerating the Activation of NO x − on Ru Nanoparticles for Ammonia Production by Tuning Their Electron Deficiency

Accelerating the Activation of NO _x ⁻ on Ru Nanoparticles for Ammonia Production by Tuning Their Electron Deficiency

In-situ covalent bonding of carbon dots on two-dimensional tungsten disulfide interfaces for effective monitoring and remediation of chlortetracycline residue

• 2D WS 2 /CDs multifunctional nanomaterial was prepared by in-situ covalent bonding. • 2D WS 2 /CDs nanocomposite could be simultaneous detection and degradation of CTC. • The possible mechanisms for the detection and degradation of CTC were investigated. • This work is expected to provide a new idea for design of multifunctional platform. In view of the increasing threat of chlortetracycline (CTC) in water to human health and the ecological environment, how to detect and remove CTC in wastewater simply and effectively remains an important and challenging task. Herein, a multifunctional platform for the simultaneous detection and degradation of CTC is developed by in-situ synthesis of carbon dots (CDs) in the two-dimensional (2D) WS 2 interface by covalent bonding. The as-prepared 2D WS 2 /CDs nanocomposites can not only be used as an intelligent fluorescence probe for CTC detection with good sensitivity (LOD = 7.5 nM) and selectivity but also has good photodegradation ability for CTC (degradation efficiency attained 85.58%). Moreover, the possible mechanisms for the detection and photodegradation of CTC by 2D WS 2 /CDs were also investigated by theoretical calculations, time-resolved fluorescence decay curves, and electron spin resonance (ESR) analyses. The exceptional photoelectric properties of 2D WS 2 /CDs are ascribed to the CDs bound onto the 2D WS 2 interface by covalent bonding forming heterojunctions, which effectively promote strong interfacial interactions between CDs and 2D WS 2 , thereby providing more effective charge transfer and enhancing the detection efficiency and photocatalytic activity. In addition, the possible degradation pathway for CTC was speculated via identification of intermediates and frontier electron density calculation. Overall, this study not only proves that the 2D WS 2 /CDs nanocomposites have great potential for the simultaneous detection and degradation of CTC in aquatic environments but also provides a novel idea for the efficient and stable design of multifunctional nanomaterials for environmental pollution monitoring and purification, which is of great significance to both practical applications and basic research.

Ar/SF6 plasma simulation for dual-frequency capacitively coupled plasma incorporating gas flow simulation and secondary electron emission

We developed the coupled calculation of plasma and gas flows in simulations for dual-frequency excited Ar/SF6 plasma. By focusing on the effect of secondary electron emission (SEE), we varied SEE coefficient γ and determined γ = 0.04 from the comparison of calculation results with the experimental results. The dependence of electron density on spatial distribution and SF6 gas partial pressure was compared between calculation and experimental results. As a result, at SF6 = 5.0 sccm, the calculated electron densities at the center and edge were almost the same as the experimental results. Furthermore, at SF6 = 2.5 sccm, the error from the experiment including the spatial distribution was in the range of −11.03 to 4.11%, and the results of coupled calculation of plasma and gas flows in simulations can reproduce the experimental results under at a SF6 partial pressure in the range from 2.5 to 5.0 sccm.

Degradation of tris(2-chloroethyl) phosphate (TCEP) by thermally activated persulfate: Combination of experimental and theoretical study

Organophosphorus esters (OPEs), one kind of the emerging contaminants with high frequency of detection, is rather refractory in natural environment, thus posing great threat to human health. This study investigated the feasibility and mechanism of tris(2-chloroethyl) phosphate (TCEP) degradation in thermally activated persulfate (TAP) system. Influence of impact factors, such as PDS dosage, temperature, initial pH, and presence of natural water matrix (Cl−, NO3−, H2PO4−, NH4+, humic acid), were evaluated. Results showed that 100% degradation of TCEP can be achieved in TAP system in 40 min at 60 °C. SO4·− as the dominant oxidant for TCEP degradation was proved by quenching experiment and verified by EPR analysis. Alkaline condition exerted great inhibitory effect by affecting the constituents of oxidative radicals. It is suggested that Cl− and H2PO4− at lower dosages promoted the degradation by stimulating ·OH production and forming oxidative radicals with better selectivity. Intermediates identified by high resolution mass spectrometer was suggested less toxic than TCEP by ECOSAR program. Meanwhile, the illustrated oxidation mechanism mainly involved radical attack at CCl bond and cleavage of CO bond, as further confirmed by frontier electron density calculation and wavefunction analysis. Moreover, cyclic degradation of TCEP indicated the constant release of SO4·− in 450 min, suggesting high efficiency and stability of PDS in TAP system. Four selected OPEs achieved complete removal in TAP system and their degradation discrepancy was further discussed based on the distinctive structures. Altogether, TAP technology can be used as an efficient method in TCEP removal with great potential for application.

Impact of functional groups on the electrocatalytic hydrogenation of aromatic carbonyls to alcohols

Electrocatalytic hydrogenation (ECH) of biomass-derived feedstocks has a critical dependence on the molecular structure of the organic and its adsorption on the electrode surface. In this study, we investigated the role of functional groups in the adsorption of the organic molecule on the charged Pd (111) surface and its subsequent effect on organic reduction in electrochemical hydrogenation of organic molecules. With three aromatic carbonyls of benzaldehyde (BZD), acetophenone (ACE), and vanillin (VAN), we rationalize molecular-scale adsorption and interfacial charge transfer processes by employing density-functional-theory based ab initio molecular dynamics simulations. We observe that the functional group and electrode charge strongly affect the proximity of organic molecule to the Pd (111) surface, where distances of aromatic ring and carbonyl group of the organic on the electrode change distinctively with functional groups and charge state of electrode, which strongly impact reduction of organics on the surface. Calculations of differential electron density show the strongest reduction with benzaldehyde via interfacial electron transfer from the charged Pd surface. We also observe that the interaction between the functional groups and solvent (VAN > BZD > ACE) significantly influence the organic interaction with the charged electrode (BZD > VAN > ACE), resulting in the net interaction energy between the organic and the electrode in the order of BZD > ACE > VAN. Experimental measurement of ECH rate also show the same trend of the net interaction energy. These results demonstrate the significance of solvent effect on the reducibility of organic molecules on electrodes.

Dipole Moment Calculations Using Multiconfiguration Pair-Density Functional Theory and Hybrid Multiconfiguration Pair-Density Functional Theory

The dipole moment is the molecular property that most directly indicates molecular polarity. The accuracy of computed dipole moments depends strongly on the quality of the calculated electron density, and the breakdown of single-reference methods for strongly correlated systems can lead to poor predictions of the dipole moments in those cases. Here, we derive the analytical expression for obtaining the electric dipole moment by multiconfiguration pair-density functional theory (MC-PDFT), and we assess the accuracy of MC-PDFT for predicting dipole moments at equilibrium and nonequilibrium geometries. We show that MC-PDFT dipole moment curves have reasonable behavior even for stretched geometries, and they significantly improve upon the CASSCF results by capturing more electron correlation. The analysis of a dataset consisting of 18 first-row transition-metal diatomics and 6 main-group polyatomic molecules with a multireference character suggests that MC-PDFT and its hybrid extension (HMC-PDFT) perform comparably to CASPT2 and MRCISD+Q methods and have a mean unsigned deviation of 0.2-0.3 D with respect to the best available dipole moment reference values. We explored the dependence of the predicted dipole moments upon the choice of the on-top density functional and active space, and we recommend the tPBE and hybrid tPBE0 on-top choices for the functionals combined with the moderate correlated-participating-orbitals scheme for selecting the active space. With these choices, the mean unsigned deviations (in debyes) of the calculated equilibrium dipole moments from the best estimates are 0.77 for CASSCF, 0.29 for MC-PDFT, 0.24 for HMC-PDFT, 0.28 for CASPT2, and 0.25 for MRCISD+Q. These results are encouraging because the computational cost of MC-PDFT or HMC-PDFT is largely reduced compared to the CASPT2 and MRCISD+Q methods.

Cooperativity and Metal–Linker Dynamics in Spin Crossover Framework Fe(1,2,3-triazolate)2

Cooperative interactions are responsible for the useful properties of spin crossover (SCO) materials─large hysteresis windows, critical temperatures near room temperature, and abrupt transitions─with hybrid framework materials exhibiting the greatest cooperativity and hysteresis of all SCO systems. However, little is known about the chemical origin of cooperativity in frameworks. Here, we present a combined experimental–computational approach for identifying the origin of cooperativity in the metal–organic framework (MOF) Fe(1,2,3-triazolate)2 (Fe(TA)2), which exhibits the largest known hysteresis window of all SCO materials and unusually high transition temperatures, as a roadmap for understanding the manipulation of SCO behavior in general. Variable-temperature vibrational spectroscopy provides evidence that “soft modes” associated with dynamic metal–linker bonding trigger the cooperative SCO transition. Thermodynamic analysis also confirms a cooperativity magnitude much larger than those of other SCO systems, while electron density calculations of Fe(TA)2 support previous theoretical predictions that large cooperativity arises in materials where SCO produces considerable differences in metal–ligand bond polarities between different spin states. Taken together, this combined experimental–computational study provides a microscopic basis for understanding cooperative magnetism and highlights the important role of dynamic bonding in the functional behavior of framework materials.

Pixel calculations using Orca or GAUSSIAN for electron density automated within the Oscail package.

Many discussions of the intermolecular interactions in crystal structures concentrate almost exclusively on an analysis of hydrogen bonding. A simple analysis of atom-atom distances is all that is required to detect and analyse hydrogen bonding. However, for typical small-molecule organic crystal structures, hydrogen-bonding interactions are often responsible for less than 50% of the crystal lattice energy. It is more difficult to analyse intermolecular interactions based on van der Waals interactions. The Pixel program can calculate and partition intermolecular energies into Coulombic, polarization, dispersion and repulsion energies, and help put crystal structure discussions onto a rational basis. This Windows PC implementation of Pixel within the Oscail package requires minimal setup and can automatically use GAUSSIAN or Orca for the calculation of electron density.

Unveiling the mechanism of imidacloprid removal by ferrate(VI): Kinetics, role of oxidation and adsorption, reaction pathway and toxicity assessment

Imidacloprid (IMI), an emerging pollutant, has high toxicity to non-target organisms. This paper presents the kinetics of IMI removal by ferrate(VI) at different pH (6.0–9.0), molar ratios ([ferrate(VI)]:[IMI]) and added Fe(III) ions. The apparent second-order rate constant (kapp) decreased with increase in pH from pH 6.0 to 9.0 (i.e., (1.2 ± 0.1) × 102 M−1 s−1 to (8.3 ± 0.3) M−1 s−1). The species-specific rate constants were obtained as k (HFeO4−) = 1.3 × 102 M−1 s−1 and k (FeO42−) = 6.9 M−1 s−1. The decreases in the concentration of HFeO4− with increase in pH caused the observed pH dependence in kapp. At pH 7.0, the removal of IMI increased with the molar ratio from 1.0 to 10.0 with complete removal at the highest ratio. The variation in pH from 6.0 to 9.0 had no obvious effect on removal of IMI. Experiments indicate that IMI removal is mainly by ferrate(VI) oxidation and to a lesser extent by Fe(III) adsorption. Mineralization of IMI was also observed (20–26%). The addition of Fe(III) ions to ferrate(VI)-IMI at pH 7.0 and 8.0 resulted in enhanced removal of IMI, but the presence of Ca2+, SO42−, HCO3−, and humic acid (HA) has negative effects. The presence of coexisting substances in river water slightly decreased IMI removal by ferrate(VI) by less than 10%. Identification of products and frontier electron density (FED) calculations demonstrated involvement of opening of the five-membered heterocyclic moiety of IMI by ferrate(VI). Toxicity assessment with NIH 3T3 fibroblasts and ECOSAR analysis indicated lower toxicity of oxidized products than parent IMI.

Dual functional cobalt-yttrium binary oxide activation of peroxymonosulfate for degradation of phenylphosphonic acid and simultaneous adsorption of phosphate product

Cobalt-yttrium binary oxide (CYBO) was successfully fabricated, which exhibited excellent catalytic performance in the activation of peroxymonosulfate (PMS) and superior adsorption capacity towards phosphate (116.3 mg-P/g). The results demonstrated that a complete degradation of phenylphosphonic acid (PPOA) within 30 min and a thorough removal of phosphate product within 60 min could be realized in the system of CYBO/PMS. CYBO also possessed superb reusability and stability, and no decline of the PPOA degradation and phosphate removal was observed during 5 cycles at initial pH 7. The decomposition of PPOA and the adsorption of phosphate were strongly dependent on solution pH. In an initial pH range of 3 to 7, both PPOA and phosphate product could be efficiently removed. However, almost no PPOA was degraded at initial pH 11. SO4•−, •OH, and 1O2 (especially SO4•− and •OH) were identified as main reactive oxygen species responsible for the PPOA degradation and the formation of phosphate product. The produced phosphate was simultaneously eliminated via anion/ligand exchange. Combined with identification of PPOA degradation intermediates via HPLC-QTOF-MS2, the calculation of frontier electron densities based on Density Functional Theory was used for proposing reasonable degradation pathways. In addition, the toxicity assessment via Toxicity Estimation Software Tool was utilized to appraise eco-environmental effect. Our findings may shed some light towards the application of CYBO in the control of organophosphorus pollution and the reduction of water eutrophication.

Atomic data and the density structures of planetary nebulae

ABSTRACT We study the density structures of planetary nebulae implied by four diagnostics that sample different regions within the nebulae: [S ii] λ6716/λ6731, [O ii] λ3726/λ3729, [Cl iii] λ5518/λ5538, and [Ar iv] λ4711/λ4740. We use a sample of 46 objects with deep spectra that allow the calculation of the electron density from these four diagnostics, and explore the impact that different atomic data have on the results. We compare the observational results with those obtained from photoionization models characterized by three different density structures. We conclude that the atomic data used in the calculations of electron density fully determine the density structures that are derived for the objects. We illustrate this by selecting three combinations of atomic data that lead to observational results that are compatible with each of the three different density structures explored with the models.

Theoretical insights into the adsorption mechanism of Cd(II) on the basal surfaces of kaolinite

Retardation of Cd(II) migration is an ongoing concern for environmental remediation, but a prevalent obstacle of the procedure originates from the lack of an atomic-scale description of the inherent mechanism for Cd(II) adsorption at mineral-water interfaces. Herein, we performed first-principles calculations and ab initio molecular dynamics (AIMD) simulations to explore the adsorption mechanism of Cd(II) on the basal surfaces of kaolinite. Representative monodentate and bidentate Cd(II) complexes were constructed on the Kln−Al(001) and Kln−Si(001̅) surfaces. The results showed that bidentate coordination of Cd(II) on the Kln−Al(001) surface was superior to all other studied models due to the favorable formation energy and better agreement with EXAFS data. The calculated electron density difference revealed the charge transfer from surface oxygen (Os) to Cd(II) upon adsorption. In particular, partial density of states (PDOS) analysis indicated that the Cd−Os bond exhibited covalent characteristics, attributed to the overlaps of Cd-5p and Os-2p orbitals in the valence band. Furthermore, radial distribution functions supported by AIMD simulations were employed to confirm the structural features of Cd(II) coordination shell at kaolinite-water interfaces. This theoretical study provides insightful guidance for future Cd(II) research to improve current assessments of contaminant remediation.

Electron density from the fragment molecular orbital method combined with density-functional tight-binding

A method for electron density calculations is developed for the density-functional tight-binding formulation of the fragment molecular orbital method with periodic boundary conditions. The effects of binding in molecular systems on the electron density are studied on water clusters, an α-helix of deka-alanine, and a protein–ligand complex revealing the effect of the polarization and charge transfer. In particular, density changes accompanying the formation of hydrogen bonds are elucidated in detail.

Reduced model of plasma evolution in hydrogen discharge capillary plasmas.

A model describing the evolution of the average plasma temperature inside a discharge capillary device including Ohmic heating, heat loss to the capillary wall, and ionization and recombination effects is developed. Key to this approach is an analytic quasistatic description of the radial temperature variation which, under local thermal equilibrium conditions, allows the radial behavior of both the plasma temperature and the electron density to be specified directly from the average temperature evolution. In this way, the standard set of coupled partial differential equations for magnetohydrodynamic (MHD) simulations is replaced by a single ordinary differential equation, with a corresponding gain in simplicity and computational efficiency. The on-axis plasma temperature and electron density calculations are benchmarked against existing one-dimensional MHD simulations for hydrogen plasmas under a range of discharge conditions and initial gas pressures, and good agreement is demonstrated. The success of this simple model indicates that it can serve as a quick and easy tool for evaluating the plasma conditions in discharge capillary devices, particularly for computationally expensive applications such as simulating long-term plasma evolution, performing detailed input parameter scans, or for optimization using machine-learning techniques.

Research on Properties of Borocarbide in High Boron Multi-Component Alloy with Different Mo Concentrations.

In this work, the microstructure, alloying element distribution, and borocarbide mechanical properties of high-boron multi-component alloy with Fe-2.0 wt.%B-0.4 wt.%C-6.0 wt.%Cr-x wt.%Mo-1.0%Al-1.0 wt.%Si-1.0 wt.%V-0.5 wt.%Mn (x = 0.0, 2.0, 4.0, 6.0, 8.0) are investigated. The theoretical calculation results and experiments indicate that the microstructure of high-boron multi-component alloy consists of ferrite, pearlite as a matrix and borocarbide as a hard phase. As a creative consideration, through the use of first-principles calculations, the comprehensive properties of borocarbide with different molybdenum concentrations have been predicted. The calculations of energy, state density, electron density and elastic constant of Fe2B crystal cell reveal that substitution of the molybdenum atom in the Fe2B crystal cell can remarkably improve its thermodynamic stability, bond strength, and covalent trend. For verifying the accuracy of this theoretical calculation, nano-indentation testing is carried out, the results of which indicate that the actual properties of borocarbide present favorable consistency with the theoretical calculations.