Electrostatic Potential Distribution Research Articles

Aqueous Stability of Zirconium Clusters, Including the Zr(IV) Hexanuclear Hydrolysis Complex [Zr6O4(OH)4(H2O)24]12+, from Density Functional Theory.

Framework materials constitute a broad family of solids that range from zeolites and metal-organic frameworks (MOFs) to coordination polymers. The synthesis of such network structures typically rely on precursor molecular building blocks. As an example, the UiO-66 MOF series is constructed of hexanuclear [Zr6O4(OH)4(CO2)12] cluster nodes and linear carboxylate linkers. Unfortunately, these Zr MOF cluster nodes cannot currently be manufactured in a sustainable way, motivating a search for "green" alternative synthesis methods. Stabilizing the hexanuclear Zr(IV) cluster (i.e., the hexamer, {Zr612+}) without the use of organic ligation would enable the use of environmentally friendly solvents such as water. The Zr(IV) tetranuclear cluster (i.e., the tetramer, {Zr48+}) can be stabilized in solution with or without organic ligands, yet the hexamer has yet to be synthesized without supporting ligands. The reasons why certain zirconium clusters are favored in aqueous solution over others are not well understood. This study reports the relative thermodynamic instability of the hypothetical hexamer {Zr612+} compared to the ubiquitous {Zr48+} tetramer. Density functional theory calculations were performed to obtain the hydrolysis Gibbs free energy of these species and used to construct Zr Pourbaix diagrams that illustrate the effects of electrochemical potential, pH, and Zr(IV) concentration. It was found that the aqueous {Zr612+} hexamer is ∼17.8 kcal/mol less stable than the aqueous {Zr48+} tetramer at pH = 0, V = 0, and [Zr(IV)] = 1 M, which is an energy difference on the order of counterion interactions. Electronic structure analyses were used to explore trends in the highest occupied molecular orbital-lowest unoccupied molecular orbital gap, frontier molecular orbitals, and electrostatic potential distribution of these clusters. The evidence suggests that the aqueous {Zr612+} hexamer may be promoted with more strategic syntheses incorporating minimal ligands and counterions.

Photoexcitation of oxazine 170 dye in aqueous solution: TD-DFT study.

The vibronic absorption spectra of OX170 dye in an aqueous solution using 40 hybrid functionals, the 6-31 + + G(d,p) basis set, and the SMD solvent model were calculated. It turned out that the long-range corrected ωB97XD functional provided the best agreement with the experiment in the positions of the main maximum and the short-wavelength shoulder. Calculations showed that this shoulder is vibronic and is not caused by a separate electronic transition. At the same time, the shoulder intensity in the calculated spectrum turned out to be lower than in the experimental one. Various parameters of the OX170 cation in the ground and excited states (IR spectra, atomic charges, dipole moments, and transition moment) were calculated. Maps of the distribution of electron density and electrostatic potential have been built. The influence of four strong hydrogen bonds of the dye with water molecules on the absorption spectrum was analyzed. It was shown that these bonds are strengthened upon OX170 excitation. It was found that explicit assignment of water molecules strongly bound to the dye leads to a redshift of the calculated spectrum by ≈15nm as a whole, and worsened its shape. Photoexcitation of the dye leads to a noticeable polarization of only one of the four considered water molecules (associated with the endocyclic nitrogen atom in the central ring of the chromophore, the electron density on which increases the most).

Effect of dielectrics on the field emission characteristics in the diode system modeling

In this article diode emission system with dielectrics on the field emitter basis is simulated. The diode system is a rotationally symmetrical electron gun with a field emission cathode on a flat substrate and a flat anode parallel to the substrate. The interior of the system domain is filled with three dielectrics. The effect of the field cathode on the electrostatic potential distribution is replaced by the effect of a finite charged line that is located at the axis of the system. The potential distribution is determined over the entire area of an electron gun. Fowler–Nordheim equation is used to calculate the emission characteristics values. The effect of dielectrics on the emission characteristics is presented.

Structure reactivity analysis for Phenylalanine and Tyrosine

Phenylalanine (Phe) is one of the amino acids that cannot be produced in the body and must be ingested through diet. Tyrosine (Tyr) is also a non-essential amino acid and can be produced by Phe hydroxylation in the liver when the dietary intake of Tyr is low. Structure analysis is very important to know the correct synthesis and the reactivity of the molecule. In this study, the characterization of Phe and Tyr molecules were investigated using quantum chemical calculations. The molecular geometry for both molecules was determined using density functional theory (B3LYP) by handling the 6-311++G(d,p) basis set. The method of TD-DFT which is based on the B3LYP/6-31++G(d,p) level, was utilized in ethanol solvent to find the electronic absorption spectra. In addition, frontier molecular orbitals, electrostatic potential and molecular charge distributions analysis were carried out by B3LYP/6-311++G(d,p) theory. The energy differences between HOMO and LUMO for Phe were obtained as 0.19851 eV, which have a good argument with the reactivity compared with tyrosine, and energy band gap was 0.20501 eV

Balancing Intermolecular Interactions between Acceptors and Donor/Acceptor for Efficient Organic Photovoltaics

AbstractPromoted by uninterrupted materials and device innovation, organic solar cells have achieved impressive development. However, the complicated intermolecular interactions inside active layers are less understood. Herein, the intermolecular interactions are studied from the dual perspectives of acceptor/acceptor (A/A) and donor/acceptor (D/A), and how these interactions synergistically control the final efficiencies. Three small molecular acceptors (SMAs) are designed with different end‐caps, which manipulate the crystallinity and electrostatic potential (ESP) distributions of acceptors, and accordingly, the A/A and D/A intermolecular interactions. The results show that SMA LA17 with low A/A interactions exhibits inferior performance around 12%, owing to its strong D/A interaction with donor PM6, which shapes too miscible morphology and increases charge recombination. Instead, LA16 with strong A/A interactions and moderate D/A interactions delivers improved bulk‐heterojunction (BHJ) networks, and therefore, enhances charge transport and diminishes geminate or trap‐assisted charge recombination. Consequently, PM6:LA16 records the competitive efficiency of up to 13.74% among the three systems. Therefore, this study deepens the synergistic or balancing effect of the D/A and A/A interactions on BHJ blends for efficient organic solar cells.

Study on the electrostatic field distribution in a typical propellant production process

To analysis the electrostatic risk in the mixing process of typical propellants, the distribution of the electrostatic field inside the cylinders was investigated. The maximum charge quantity (−1.895 μC kg−1) and relative dielectric constant (1.88) of 11/7 propellant were obtained through experiments. Based on Ansoft Maxwell electrostatic field numerical analysis, the electrostatic field intensity and potential distribution inside the cylinder were obtained. The maximum electrostatic field intensity and potential of 11/7 propellant increased with the propellant height. When the propellant height increased to 290 mm with a diameter of 300 mm, the maximum field intensity at the bottom was 15.1 MV/m.

Application of terahertz spectroscopy combined with density functional theory to analysis of intermolecular weak interactions for coumarin and 6-methylcoumarin

The terahertz (THz) absorption spectra of coumarin and 6-methylcoumarin have been investigated by terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.4 to 2.8 THz. Density functional theory (DFT) calculations, both with and without London force dispersion corrections, have been used for the assignment of the experimental THz spectra. To thoroughly interpret the spectrum information, we used potential energy distribution (PED) method to assign the vibrational modes of the absorption peaks, and identify the origin of the absorption peaks by electrostatic potential (ESP) and van der Waals (vdW) potential distribution analysis method. The results show that absorption peaks both for coumarin and 6-methylcoumarin are caused by electrostatic interaction in the lower frequency range, while vdW interaction in the higher frequency. Moreover, the potential energy distribution of electrostatic and vdW between them is basically the same, and it led to the similarity of THz spectra between coumarin and 6-MC. This work has demonstrated that using THz spectroscopy combined with DFT calculations is an effective way to analysis of intermolecular weak interactions and biomolecules with similar structures.

Interplay of Interfacial Viscosity, Specific-Ion, and Impurity Adsorption Determines Zeta Potentials of Phospholipid Membranes.

Ion-specific induced changes of the ζ-potential of phospholipid vesicles are commonly used to quantify the affinity of different ions to the lipid interface. The negative ζ-potential of zwitterionic net-neutral phospholipid vesicles in neat water, which changes sign and increases in solutions of NaCl or KCl, is a phenomenon consistently observed in experiments but not fully understood theoretically. Using atomistic molecular dynamics simulations in the presence of applied electric fields which drive electroosmotic flows, in combination with an electrostatic continuum model based on the modified Poisson-Boltzmann and Helmholtz-Smoluchowski equations, we study the electrokinetic and electrostatic properties as well as the specific ion affinities to the phospholipid-water interface, in order to resolve these puzzling observations. Our modified continuum equations account for the dielectric profile at the lipid-water interface, ion-specific interactions between ions and the lipid-water interface, and the interfacial viscosity profile, which are all extracted from our atomistic simulations and rather accurately predict ion-density and electrostatic-potential distributions as well as ζ-potentials in comparison with our atomistic simulations. Our continuum model can explain experimental ζ-potentials only when we assume minute amounts of surface-active anionic impurities in the aqueous solution. In fact, the amount of impurities needed to explain the experimental data increases linearly with the salt concentration, suggesting that surface-active species, which might be already present in the lab water or lipid samples, could further be introduced through the added salt.

Novel methoxyquinoline derivative: Synthesis, characterization, crystal structure, Hirshfeld surface, thermodynamic properties, and quantum chemical calculation of 3,6,8-trimethoxyquinoline

In this study, we describe the synthesis and structural characterization of novel 3,6,8-trimethoxyquinoline (2) by X-ray, FT-IR, NMR analysis, and its computational investigations. The molecular geometry of title coumpound was also optimized by using density functional theory (DFT/B3LYP) and Hartree–Fock (HF) methods with the 6-311 G(d,p) basis set, and geometric parameters were compared with the experimental data. Theoretical calculations are a good way for obtaining comprehensive information about global and local chemical activity, and chemical and molecular properties that reveal the nucleophilic and electrophilic nature. Molecular electrostatic potential (MEP) distribution, thermodynamic parameters, frontier molecular orbitals (FMOs), Fukui functions, and net charge analysis of (2) were also investigated. Also, the interactions between the molecule with DNA bases such as guanine, adenine, thymine, and cytosine were investigated by using the electrophilicity-based charge transfer (ECT) method and charge transfer (ΔN) for investigating the charge transfer, electrophilic, and nucleophilic nature.

A Lanthanide Complex Fluorescent Probe for the Detection of Melamine.

Melamine has been illegally adulterated in dairy food because of the rich nitrogen content and stable chemical properties in recent years. Therefore, the detection of melamine is of great significance for food safety supervision and human health protection. As melamine is a weak fluorescent substance, it is difficult to detect melamine directly by fluorescence spectroscopy. In this work, we found that melamine can significantly enhance the emission of the tetracycline-europium (EuTC) complex at 616 nm. Therefore, we took EuTC complex as a fluorescent probe to detect melamine. According to the characterizations of absorption spectra, molecular electrostatic potential distribution, and the time-resolved spectra, we speculated that tetracycline and melamine may form a complex through hydrogen bonding interaction in the melamine-EuTC reaction system, causing the melamine closer approach to Eu3+ and reducing the non-radiative energy loss of water molecules to Eu3+, which significantly enhanced the fluorescence intensity of EuTC. The fluorescence intensity of EuTC complex with melamine concentration in the range of 0.5-40.0 μM shows a good linear relationship, and the correlation coefficient is 0.9951 with the detection limit of 7.85 × 10-8 M. It shows a high sensitivity for the EuTC complex as a fluorescent probe to detect melamine, which provides a supplement and extension for the detection of melamine by fluorescence spectroscopy.

Impact of Electrostatic Interaction on Bulk Morphology in Efficient Donor–Acceptor Photovoltaic Blends

AbstractBulk heterojunctions comprising mixed donor (D) and acceptor (A) materials have proven to be the most efficient device structures for organic photovoltaic (OPV) cells. The bulk morphology of such cells plays a key role in charge generation, recombination, and transport, thus determining the device performance. Although numerous studies have discussed the morphology‐performance relationship of these cells, the method of designing OPV materials with the desired morphology remains unclear. Herein, guided by molecular electrostatic potential distributions, we have established a connection between the chemical structure and bulk morphology. We show that the molecular orientation at the D‐A interface and the domain purity in the blend can be effectively modulated by modifying the functional groups. Enhancing the D‐A interaction is beneficial for charge generation. However, the resulting low domain purity and increased charge transfer ratio in its hybridization with the local excitation states lead to severe charge recombination. Fine‐tuning the bulk morphology can give balanced charge generation and recombination, which is crucial for further boosting the efficiency of the OPV cells.

Impact of Electrostatic Interaction on Bulk Morphology in Efficient Donor-Acceptor Photovoltaic Blends.

Bulk heterojunctions comprising mixed donor (D) and acceptor (A) materials have proven to be the most efficient device structures for organic photovoltaic (OPV) cells. The bulk morphology of such cells plays a key role in charge generation, recombination, and transport, thus determining the device performance. Although numerous studies have discussed the morphology-performance relationship of these cells, the method of designing OPV materials with the desired morphology remains unclear. Herein, guided by molecular electrostatic potential distributions, we have established a connection between the chemical structure and bulk morphology. We show that the molecular orientation at the D-A interface and the domain purity in the blend can be effectively modulated by modifying the functional groups. Enhancing the D-A interaction is beneficial for charge generation. However, the resulting low domain purity and increased charge transfer ratio in its hybridization with the local excitation states lead to severe charge recombination. Fine-tuning the bulk morphology can give balanced charge generation and recombination, which is crucial for further boosting the efficiency of the OPV cells.

Selective determination of epinephrine using electrochemical sensor based on ordered mesoporous carbon / nickel oxide nanocomposite

A nanocomposite of ordered mesoporous carbon/nickel oxide (OMC-NiO) was synthesized by hard-templating method. The nanocomposite remained ordered mesostructure and high surface area with the NiO nanocrystals embedded in the wall of the OMC. A sensitive sensor for electrochemical detection of epinephrine (EP) was developed with GCE modified by OMC-NiO nanocomposite. Cyclic voltammogram (CV) and differential pulse voltammetry (DPV) were used as the techniques to explore the electrochemical behavior of EP on OMC-NiO/GCE surface. The result showed that the electrode demonstrated better electrocatalytic performance to EP compared to that seen at OMC/GCE. Under the optimum condition, DPV measurements of the electrode response displayed a linear detection range for 8.0 × 10−7 to 5.0 × 10−5 M with a detection limit of 8.5 × 10−8 M (S/N = 3). It is worth noting that the electrocatalytic redox mechanism of EP on the electrode have studied through experiments and calculations (cyclic voltammetry and molecular electrostatic potential distribution). Moreover, the electrocatalytic behavior for the oxidation of EP and uric acid (UA) on OMC-NiO/GCE surface was investigated. The result showed that the sensor can be used to selectively determinate EP in the presence of an excesses of UA. Finally, the developed sensor was successfully applied to the determination of EP in spiked human blood serum and EP injection with satisfactory results.

Tailoring Noncovalent Interactions to Activate Persistent Room‐Temperature Phosphorescence from Doped Polyacrylonitrile Films

AbstractOrganic phosphors exhibiting room‐temperature phosphorescence (RTP) in amorphous phase are good candidates for optoelectronic and biomedical applications. In this proof‐of‐concept work, a rational strategy to activate wide‐color ranged and persistent RTP from amorphous films by embedding electron‐rich organic phosphor into electron‐deficient matrix polyacrylonitrile (PAN) is presented. Through tailoring noncovalent interactions between the electron‐deficient PAN matrix and electron‐rich organic phosphors, an ultralong lifetime of 968.1 ms is obtained for doped film TBB‐6OMe@PAN. Control experiments conducted on the polymers polymethyl methacrylate (PMMA) and polystyrene (PS) without electron‐withdrawing groups, and organic phosphors containing electron‐withdrawing groups indicate that the persistent RTP of doped films may be triggered by strong electrostatic interactions between electron‐deficient PAN and electron‐rich organic phosphor. Further theoretical calculations including electrostatic potential distributions, binding energies, and energy decomposing analysis demonstrate that both electrostatic and dispersion interactions between electron‐deficient PAN and electron‐rich organic phosphor are responsible for the activation of persistent RTP of doped films. In addition, the doped film TBB‐6OMe@PAN still maintains brightness even after soaking in water for 12 weeks. This excellent water resistance not only is favorable for future applications but also demonstrates an advantage of electrostatic and dispersion interactions over hydrogen bonding interactions.

Novel coagulation waste-based Fe-containing carbonaceous catalyst as peroxymonosulfate activator for pollutants degradation: Role of ROS and electron transfer pathway

A facile one-step pyrolysis method was employed to prepare an iron containing carbonaceous catalyst using coagulation waste (CW) from paper mill. The catalyst (noted as PMCW) was used to activate peroxymonosulfate (PMS) for decomposition of Reactive Red 2 (RR2). The degradation mechanism was analyzed by reactive oxygen species (ROS) scavenging experiments, electron spin resonance spectroscopy, electrochemical measurements, selective deactivation of the functional groups on the catalyst surface, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Results showed that, besides ROS (•OH, SO4•- and 1O2), electron transfer pathways induced by −OH functional groups and the π-π* system are involved in the degradation mechanism of RR2. Concerning different decomposition pathways, seven intermediates were identified, and three important steps, including attack on the azo group, cleaving the N9−C10 bond, and opening the naphthalene ring, were deduced via application and analysis of quadrupole time-of-flight liquid chromatography/mass spectrometry (QTOF LC/MS) and density functional theory (DFT) calculations based on Fukui indices and electrostatic potential (ESP) distributions. This work not only provides a novel facile recycling strategy of industrial waste from paper manufacturing to good carbonaceous catalysts but also deepens the understanding of the mechanisms of PMS activation with carbonaceous materials.

Electrostatic potential measurement at the Pt/TiO2 interface using electron holography

The interface of Pt/TiO2 plays an essential role in device engineering and chemical reactions. Here, we report the electrostatic potential distribution of a Pt/TiO2 interface by electron holography. The decrease in the electrostatic potential exists at TiO2 in the vicinity of the interface, indicating the presence of negative charge due to electron transfer from TiO2 and Pt. The decrease in the electrostatic potential can be understood in the difference in work functions between Pt and TiO2. This study reveals the interplay between Pt and TiO2 and the usefulness of electron holography for probing the potential in nanoscale interfaces.

Analytical modelling and simulation of negative capacitance junctionless FinFET considering fringing field effects

Abstract This article proposes an analytical model for channel potential and threshold voltage for negative capacitance junctionless FinFET (NC-JL FinFET). The Poisson's equation has been solved in collaboration with Landau–Khalatnikov equation to obtain analytical model for electrostatic potential distribution, threshold voltage and DIBL. The effect of fringing field on the potential distribution function due to source/drain spacer has also been taken into consideration. The results of proposed models are also validated and compared with simulated results of Sentaurus TCAD device simulator. The effect of various physical parameters like thickness of ferroelectric layer, fin thickness, spacer length, gate dielectric constant etc. on the performance of device has been studied. Further, the performance is also examined for different technology nodes and its (in context of) SCEs.

Spreadsheet analysis of the field-driven start-up flow in a microfluidic channel.

We discuss, in this article, the solution method of the unsteady electroosmotic flow of Newtonian fluid in a square microfluidic channel cross-section in the framework of spreadsheet analysis. We demonstrate the implementation of the finite difference scheme, which is used for the discretization of the transport equations governing the flow dynamics of the present problem, in the spreadsheet tool. Also, we have shown the implementation details of different boundary conditions, which are typically used for the underlying electrohydrodynamics in a microfluidic channel, in the spreadsheet analysis tool. We show that the results obtained from the spreadsheet analysis match accurately with the numerical solutions for both the electrostatic potential distribution and the flow velocity. Our results of this analysis justify the credibility of the spreadsheet tool for capturing the intricate details of the electrically actuated microflows during the initial transiences, that is, for the start-up flows and the phenomenon due to the electrical double layer effect, quite effectively. The inferences of this analysis will open up a new research paradigm of microfluidics and microscale transport processes by providing the potential applicability of the spreadsheet tools to obtain the flow physics of our interest in a very intuitive and less expensive manner.

Extraction performance and mechanism of TBP in the separation of Fe3+ from wet-processing phosphoric acid

• The TBP is an effective extractant to remove Fe 3+ from phosphoric acid containing Cl − . • The Fe 3+ was removed completely by a counter-current three-stages extraction. • Fe 3+ was extracted in the form of HFeCl 4 and 2TBP·HFeCl 4 is the formed complex. • Each HFeCl 4 combines two TBP molecules on the opposite sides. • Fe O{TBP} is formed in the extraction process with a bond energy greater than 165 kJ/mol. Fe 3+ is an impurity of the raw phosphoric acid from wet-process route and the waste phosphoric acid from the etching process of electronic industry. The effects of temperature, the Cl − content and TBP dosage on the extraction performance of synthesized extractants to Fe 3+ in raw phosphoric acid from HCl wet-process route were investigated systematically. The results show that the extractant containing 12.5 vol% TBP and 87.5 vol% kerosene effectively extracted Fe 3+ at 293.15 K from raw phosphoric acid containing 15.8 wt% Cl − . The extraction efficiency of 100% was realized by counter-current three-stage extraction. The extract phase was characterized by FT-IR and UV–vis. The results show that Fe 3+ was extracted by TBP with the form of HFeCl 4 . The interaction between TBP and HFeCl 4 was simulated by DFT (density functional theory). The lowest energy structure, electrostatic potential distribution, energy change, bond level analysis, electron transfer, frontline molecular orbital and other information of the possible complex were simulated systematically. The results of the characterization of the extraction phase and DFT simulation were used to clarify the extraction mechanism and the structure of the complex. The simulation results show that the lone-pair electrons of the P O double bond in TBP has a strong complexation interaction with the empty orbital of HFeCl 4 and a strong bond Fe O{TBP} is formed in the extraction process. The bond length of formed Fe O{TBP} is 2.05A, the LBO bond level of Fe O{TBP} is 0.076 (0.075), the Mayer bond level of Fe O{TBP} is about 0.16, the ρ b values of Fe O{TBP} bond critical points range from 0.252 to 0.271 e − /bohr 3 . A minimum electrostatic potential of −50.59 kcal/mol is existed in TBP at the vicinity of O atom in P O double bond. Two maximum electrostatic potential of 69.43 kcal/mol and 69.92 kcal/mol are distributed symmetrically on the opposite sides of the Fe vicinity of HFeCl 4 . Each HFeCl 4 molecule combines two TBP molecules on the opposite sides, and the binding sites are near the O atom of the P O double bond of TBP and near the Fe atom of HFeCl 4 . The absolute value of the binding energy is greater than 165 kJ/mol. The complexation reaction of TBP and HFeCl 4 occurs through the surface electrostatic potential attraction and molecular orbital complementation forms. The results are helpful to understand the extraction mechanism of TBP to extract Fe 3+ from phosphoric acid.

Experimental and Molecular Dynamics Simulation Study on the Effects of the Carbon Chain Length of Gemini Surfactants on the Inhibition of the Acid-Rock Reaction Rate.

A series of gemini surfactants were synthesized to examine their adsorption properties. The properties of gemini surfactants, including critical micelle concentration, electrostatic potential distributions, charge, occupied volume, lowest unoccupied molecular orbital (LUMO), and highest occupied molecular orbital (HOMO), were evaluated using conductivity and density functional theory (DFT) calculations. The calculation results indicated that the electrostatic potential distributions were similar among the four gemini surfactants. Moreover, surfactants with longer carbon chains are more likely to be oblique on the rock surface according to the energy gap between the HOMO of the surfactants and the LUMO of the calcite surface. Experimental tests and molecular dynamics (MD) simulations were conducted to analyze the calcite-surfactant interactions. Combined with the free energy (ΔG) based on the contact angle and adsorption energy (E) based on MD simulation, the adsorption ability increases as the carbon chain length decreases. MD simulation is used to understand the form of surfactant molecules on the calcite at an atomic scale at different times. An obvious aggregation of gemini surfactants was found with an increase in the carbon chain length, which reduces the adsorption density and covered area of the surfactant. The adsorption behavior of the gemini surfactant is beneficial for isolating H+ transfer and retarding the acid reaction with the rock. The retarding ability and etching morphology were studied by acid etching. The acid-rock reaction rate showed that 12-4-12 had the best inhibition performance. Meanwhile, the uneven surface pattern following 12-4-12 etching is beneficial for maintaining the acid fracturing conductivity.