Redistribution Of Charge Density Research Articles

Adsorption of NH3 and NO2 Molecules on Sn-Doped and Undoped ZnO (101) Surfaces Using Density Functional Theory

The adsorption and interaction mechanisms of gaseous molecules on ZnO surfaces have received considerable attention because of their technological applications in gas sensing. The adsorption behavior of NH3 and NO2 molecules on undoped and Sn-doped ZnO (101) surfaces was investigated using density functional theory. The current findings revealed that both molecules adsorb via chemisorption rather than physisorption, with all the adsorption energy values found to be negative. The calculated adsorption energy revealed that the adsorption of the NH3 molecule on the bare ZnO surface is more energetically favorable than the adsorption of the NO2 molecule. However, a stable adsorption configuration was discovered for the NO2 molecule on the surface of the Sn-doped ZnO surface. Furthermore, the adsorption on the undoped surface increased the work function, while the adsorption on the doped surface decreased. The charge density redistribution showed charge accumulation and depletion on both adsorbent and adsorbate. In addition, the density of states and band structures were studied to investigate the electronic behavior of NH3 and NO2 molecules adsorbed on undoped and Sn-doped ZnO (101) surfaces.

High‐Energy‐Density Supercapacitors Based on High‐Areal‐Specific‐Capacity Ti3C2Tx and a Redox‐Active Organic‐Molecule Hybrid Electrode

AbstractPhotorechargeable supercapacitors are perfect energy storage devices, particularly for solar cells that output electricity only during sunshine hours. The lower energy density of supercapacitors is due to fewer redox‐active sites, poor electrolyte accessibility at the electrodes, and charge loss during charge transfer from solar cells to the supercapacitor. Here, an electrolyte‐accessible organic–inorganic hybrid electrode with synergistic pseudocapacitance of Ti3C2Tx and high theoretical specific capacity CO active centers to enhance the energy density of the supercapacitor is proposed. Density functional theory (DFT) calculations show that the covalent cross‐linking of organic molecules changes the charge density redistribution of Ti3C2Tx, enhances ion absorption and storage, and increases the energy density of the supercapacitors. Based on these DFT calculation results, hybrid electrodes are successfully prepared using p‐phenylene diisocyanate to covalently cross‐link pseudocapacitors Ti3C2Tx with anthraquinone such as 1‐hydroxyanthraquinone (HA) or 1‐amino‐4‐bromoanthraquinone‐2‐sodium sulfonate (ABS). The Ti3C2Tx‐HA hybrid electrodes exhibit high areal specific capacity (2532.5 mF cm−2), excellent ion absorption storage capability, and long‐term stability. The asymmetric supercapacitor yields a decent area specific capacity (1686.72 mF cm−2 at 0.25 mA cm−2) and energy density (599.72 mWh cm−2 at a power density of 200 mW cm−2). These high‐energy‐density supercapacitors are coupled with perovskite solar cells to prepare photorechargeable supercapacitors with fast energy storage.

Synthesis of Fe-Nx site-based iron-nitrogen co-doped biochar catalysts for efficient removal of sulfamethoxazole from water by activation of persulfate: Electron transfer mechanism of non-free radical degradation

Fe-N co-doped carbon materials (Fe-NC) have drawn increasing attention in advanced oxidation due to their unique structure and significant promise in heterogeneous catalysis. Herein, a Fe-N co-doped biochar catalyst was prepared by a simple pyrolysis method and was applicated to activate persulfate (PS) for the degradation of sulfamethoxazole (SMX) in wastewater. The catalytic performance of Fe-NBC was proportional to the pyrolysis temperature, and Fe-NBC-800 exhibited excellent PS activation performance with larger specific surface area (254.3 m2/g), higher defect (ID/IG = 1.04). Fe-NBC-800 exhibits high stability and reusability over multiple cycles, high catalytic activity over a wide pH range of 3–9 and good tolerance to inorganic anions. The introduction of nitrogen and iron into the carbon lattice leads to a redistribution of charge density in graphitic carbon, enhancing the interaction of PS with Fe-NBC-800 surface to form surface complexes and promoting charge transfer. Five major SMX degradation pathways are proposed, including the oxidation of nitro on the aniline ring, the breakage of S-N bond and the ring opening of isoxazole ring. This study provides new ideas for the design of Fe-NC catalysts in the field of advanced oxidation.

Electronic structure of representative band-gap materials by all-electron quasiparticle self-consistent GW calculations

In this work, we report results of the quasiparticle self-consistent GW method within the framework of the linearized augmented plane-wave method. The impact of self-consistency on the electronic structure is investigated with the examples of nine semiconductors and insulators, namely, Ar, Si, SiC, C, BN, LiF, MgO, CaO, and GaAs. Possible reasons for discrepancies between different studies and implementations are discussed. For LiF, MgO, and CaO, we assess the charge-density redistribution upon self-consistency. For a representative set of materials, we investigate and confirm the absence of (any) starting-point dependence. The off-diagonal terms in the self-energy matrix are found to considerably impact the electronic structure. For better reproducibility and quality assessment, we describe the implementation of QSGW in the all-electron full-potential code exciting.

Fe Engineering on Ru Nanosheets for Enhanced Hydrogen Evolution in pH-Universal Media.

Fe-modified Ru nanosheets are achieved via preintercalated Al species serving as the self-sacrificial template. Benefiting from the amphoteric feature of Al and strong corrosion of Fe3+ ions, Fe is effectively incorporated into pristine Ru nanosheets. Correspondingly, the surface oxophilicity is improved, promoting the Volmer step. The charge density redistribution weakens hydrogen combination on Ru and thus accelerates the desorption kinetics (Heyrovsky step). Meanwhile, more defective sites are exposed, leading to an enhanced hydrogen production in pH-universal electrolytes.

Prussian blue analogue assisted formation of iron doped CoNiSe2 nanosheet arrays for efficient oxygen evolution reaction

Electrochemical water splitting is a promising approach to produce hydrogen gas, but sluggish four-electron transfer of the oxygen evolution reaction (OER) severely limits the overall energy conversion efficiency of water splitting. Herein, as an excellent OER electrocatalyst, a technique of synthesizing Fe doped CoNiSe2 nanosheet (Fe-CoNiSe2) whole series using CoFe prussian blue analog produced by Co-ZIF-L reaction as a template is proposed here. The introduction of iron ions promotes the redistribution of the cobalt-nickel charge density, which enhances the OER kinetics. In view of the abovementioned points, Fe-CoNiSe2/NF has excellent activity, electrocatalytic properties and excellent stability in alkaline media, which only demands a lower overpotential of 244 mV and 271 mV to deliver a current density of 10 mA cm−2 and 50 mA cm−2, respectively. The material also exhibits excellent stability for at least 24 h during the OER process. This work may provide some new insights into the assembly of advanced and highly-active materials for a variety of other energy conversion applications.

Ordered mesoporous carbon spheres assisted Ru nanoclusters/RuO2 with redistribution of charge density for efficient CO2 methanation in a novel H2/CO2 fuel cell

Efficiently reducing carbon dioxide (CO2) into carbon chemicals and fuels is highly desirable due to the rapid growth of atmospheric CO2 concentration. In prior work, we described a unique H2/CO2 fuel cell driven by low-valued waste heat, which not only converts CO2 to methane (CH4) but also outputs electrical energy, yet the CO2 reduction rate needs to be urgently improved. Here, a novel Ru-RuO2 catalyst with heterostructure was grafted on mesoporous carbon spheres by in situ partially reducing RuO2 into ultrasmall Ru clusters (∼1 nm), in which heteroatom-doped carbon spheres as a matrix with excellent conductivity and abundant pores can not only easily confine the formation of Ru nanocluster but also are beneficial to the exposed active sites of Ru complex and the mass transport. Compared to pure RuO2 nanoparticles supported on carbon spheres, our composite catalyst boosts the CO2 conversion rate by more than 5-fold, reaching a value of 382.7 μmol gcat.-1h−1 at 170 ℃. Moreover, a decent output power density of 2.92 W m−2 was obtained from this H2/CO2 fuel cell using Ru-RuO2 embedded carbon spheres as a cathode catalyst. The Ru-RuO2 heterostructure can modify the adsorption energy of CO2 and induce the redistribution of charge density, thus boosting CO2 reduction significantly. This work not only offers an efficient catalyst for this novel H2/CO2 fuel cell but also presents a facile method to prepare Ru nanoclusters.

High thermoelectric figure of merit for GeS/phosphorene 2D heterostructures: A first-principles study

2D materials, such as graphene, transition metal dichalcogenides, and black phosphorus (i.e., phosphorene), have attracted wide interest as efficient thermoelectric materials. Herein, we propose GeS/phosphorene (GeS/BP) heterostructure as a promising high-performance thermoelectric material. We have investigated the electronic structure and the thermoelectrical properties of the GeS/BP 2D system using first-principles calculations combined with the semi-classical Boltzmann transport theory. We have also addressed the effect of temperature and chemical potential on its transport properties. Our calculations revealed a high thermoelectrical figure of merit (ZT) of 2.53 for the GeS/BP system. Interestingly, ultrahigh room temperature ZT values amounting to 14.01 and 33.39 could be attained through p-type doping of the GeS/BP heterostructures. We ascribe the remarkably high ZT to the increase of the Seebeck coefficient in the system and the enhanced charge density redistribution at the GeS/BP interface. These findings highlight a promising strategy to achieve high-performance thermoelectric materials through nanostructuring of 2D materials.

Resolution of Intramolecular Dipoles and a Push-Back Effect of Individual Molecules on a Metal Surface

Molecules consisting of a donor and an acceptor moiety can exhibit large intrinsic dipole moments. Upon deposition on a metal surface, the dipole may be effectively screened and the charge distribution altered due to hybridization with substrate electronic states. Here, we deposit ethyl-diaminodicyanoquinone molecules, which exhibit a large dipole moment in the gas phase, on a Au(111) surface. Employing a combination of scanning tunneling microscopy and noncontact atomic force microscopy, we find that a significant dipole moment persists in the flat-lying molecules. Density functional theory calculations reveal that the dipole moment is even increased on the metal substrate as compared to the gas phase. We also show that the local contact potential across the molecular islands is decreased by several tens of meV with respect to the bare metal. We explain this by the induced charge-density redistribution due to the adsorbed molecules, which confine the substrate’s wavefunction at the interface. Our local measurements provide direct evidence of this so-called push-back or cushion effect at the scale of individual molecules.

S vacancies in 2D SnS2 accelerating hydrogen evolution reaction

Precise manipulation of atomic defects is essential for modulating the intrinsic properties of two-dimensional (2D) materials. In this study, sulfur (S) atoms are accurately knocked out in the 2D basal plane of pure tin disulfide (SnS2). By varying the annealing temperatures (250–350°C), SnS2 with different S vacancy concentrations (Vs−SnS2) can be obtained. When SnS2 is annealed at 350°C for 5 h, the S vacancies in the forms of single S atom and double S atoms could reach up to 30.5%. The Vs−SnS2 is tested in the microelectrocatalytic hydrogen evolution reaction (HER). Vs−SnS2 with S vacancies of 30.5% generates superior catalytic performance, with a Tafel slope of 74 mV dec−1 and onset potential of 141 mV. The mechanism has been proposed. First, computation confirms that the absence of S atoms prompts surface charge modulation and enhances electronic conductivity. In addition, the under-coordinated Sn atoms adjacent to S vacancy introduce the lattice distortion and charge density redistribution, which are beneficial to hydrogen binding in HER. In short, accurate knockout of specific atoms by controlling the annealing temperature is a promising strategy to explore structure-dependent properties of various 2D materials.

Two-band superconductivity through structural and electronic reconstruction on interface: YBa2Cu3O7/LaAlO3(001)

Novel physical phenomena arising from the complex interplay between the spin, charge, orbital, and lattice orders can emerge in perovskite-type oxide heterostructures. Here, we investigate the lattice and electronic structures on the interface of the YBa2Cu3O7/LaAlO3 heterostructure prepared by pulsed laser deposition with the combination of spherical aberration-corrected scanning transmission electron microscopy and density functional theory. Both reconstructed and normal interfaces are observed at sub-angstrom resolution, and these superconducting planes closest to the corresponding interface known as CuO2(a) and CuO2(c) planes, respectively. Due to the lattice reconstruction and charge density redistribution, CuO2(a) plane moves closer to the reconstructed interface with bond length of in-plane Cu and apical oxygen reduced. Consequently, the d3z2−r2 orbital loss electrons further results in two orbitals (dx2−y2 and d3z2−r2) crossing the Fermi level, showing two-band superconductivity behavior at the reconstructed interface. However, the CuO2(c) plane remains unaffected due to the protection of the charge reservoir layer at the normal interface and exhibits electronic structures similar to bulk cuprate superconductors, where only dx2−y2 orbitals contribute to the states at the Fermi level. These results suggest that the interfacial reconstruction might be a possible pathway to manipulate the electronic structures of the superconducting oxide heterostructures.

The calculated energies and charge and spin distributions of the excited GR1 state in diamond.

This paper reports the energies and charge and spin distributions of both the vertically excited and fully relaxed GR1 states of the neutral singlet vacancy in diamond obtained from direct Δ-SCF calculations used previously to describe the low-lying excited states in AFII NiO and α-Al2O3. The calculations are based on the B3LYP functional in its standard form, with a C basis set that is identical to that which was used previously in numerous calculations of the ground state properties of defective diamond. Both the vertically excited and thermally relaxed GR1 states are predicted to be excitonic and insulating, with extensive re-distribution of charge and spin density and back-donation to the donor site. The present calculations suggest that the triplet state makes no contribution to the GR1 excitation. The predicted energy of the zero phonon line (1.57eV) compares with the observed value of 1.67eV, which also suggests that the GR1 state is neutral. The bandgaps lead to an estimate of the next higher (GR2) excited state energy, which is close to that found in the observed spectra. Similar calculations are used to predict the energies of the higher gap states at (5.0-5.5) eV, including the bulk value of 7.3eV, which compares with the experimental value of (7.3-7.4) eV. An explanation is suggested as to why only the GR1 luminescence is observed. This paper also suggests an alternative channel for the recovery of the ground state in photoluminescence studies.

Understanding Competitive Phosphate and Silicate Adsorption on Goethite by Connecting Batch Experiments with Density Functional Theory Calculations.

Despite the biogeochemical importance of phosphate fate and transport in aquatic environments, little is known about how competition with other common aqueous oxyanions affects its retention by mineral surfaces. Here, we examined the competitive uptake of phosphate and silicate on goethite over a wide pH range, using batch measurements supported by DFT calculations. The results show selective adsorption of phosphate at pH < 4 and silicate at pH > 10 with little to no competitive effect. However, between 4 < pH < 10, the total phosphate and silicate loading was found to be almost equal to that of silicate loading from single-component solution, revealing a proportionate competition for surface site types and a competitive effect controlling their mutual retention. DFT-calculated adsorption energies and charge density redistributions for various surface complexes on different charged (101) and (210) facets are consistent with the trends observed in batch measurements, suggesting that the observed behavior reflects the primary controlling influence of goethite surface chemistry at the molecular scale. An important implication is that at the circumneutral pH in most environmental systems, where iron oxyhydroxides comprise much of the reactive interfacial area, unbound phosphate concentrations may be strongly controlled by dissolved silicate concentration, and vice versa.

Formation of oxygen vacancies in Li-rich Mn-based cathode material Li&lt;sub&gt;1.167&lt;/sub&gt;Ni&lt;sub&gt;0.167&lt;/sub&gt;Co&lt;sub&gt;0.167&lt;/sub&gt;Mn&lt;sub&gt;0.5&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;

Using the first-principles method based on the density functional theory, the oxygen vacancy formations in the lithium-rich manganese-based ternary cathode material Li&lt;sub&gt;1.167&lt;/sub&gt;Ni&lt;sub&gt;0.167&lt;/sub&gt;Co&lt;sub&gt;0.167&lt;/sub&gt;Mn&lt;sub&gt;0.5&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; are calculated. The changes of oxygen vacancy formation energy with temperature, oxygen partial pressure and point defects in the material are discussed, meanwhile, the effect of oxygen vacancies on the capacity is also discussed. The calculation results show that the increase of temperature and the decrease of oxygen partial pressure can lead the formation energy of an oxygen vacancy to decline. For the charged oxygen vacancies (&lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$ {\mathrm{V}}_{\mathrm{O}}^{+1} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$ {\mathrm{V}}_{\mathrm{O}}^{+2} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;), the formation energy of an O-vacancy increases with Fermi level increasing. It is also found that the presence of an oxygen vacancy will trigger off a very local charge density redistributions, mainly around the neighboring Mn ions next to the O-vacancy. Furthermore, the effects of point defects, including cation vacancies and substitutional defects in the vicinity of the O-vacancy, on the formation energy of O-vacancy are also calculated. The results show that the presence of Mn vacancy near the O-vacancy is beneficial to the formation of the O-vacancy. In addition, the formation of oxygen vacancy is suppressed when the Mn atoms near the O-vacancy are substituted by the Mo or Fe atoms.

Excited-state intramolecular double proton transfer mechanism associated with solvent polarity for 9,9-dimethyl-3,6-dihydroxy-2,7-bis(4,5-dihydro-4,4-dimethyl-2-oxazolyl)fluorene compound

Excited-state intramolecular proton transfer (ESIPT) has been well investigated in recent years, whereas we investigated the system containing double hydrogen bonds. We explore the influence of solvent polarity on the proton transfer mechanism for 9,9-dimethyl-3,6-dihydroxy-2,7-bis(4,5-dihydro-4,4-dimethyl-2-oxazolyl)fluorene compound ((Oxa-OH)2). We consider three solvents with different polarities: cyclohexane, chloroform and acetonitrile. Various analytical methods indicate that hydrogen bonding is enhanced in the first excited state, which facilitates the proton transfer within the excited-state molecule. The frontier molecular orbital theory is employed to demonstrate that the system is subjected to photoexcitation to generate charge density redistribution. Three-dimensional potential energy surfaces are also constructed along the direction of hydrogen bond elongated, and their corresponding projection in the X-axis and Y-axis planes are plotted. The comparison of the potential barriers and the transition state structures of each proton transfer path reveals the excited-state intramolecular single proton transfer mechanism of the system. By comparing the potential barriers in different solvents, we also propose a mechanism that can modulate the excited-state proton transfer by changing the solvent polarity.

First-Principles Studies on the Formation of Oxygen Vacancies in Li2CoSiO4

The existence of oxygen vacancy has a significant effect on the structural and electronic properties of Li2CoSiO4. Herein, the formation energy of an oxygen vacancy (V O) in Li2CoSiO4 in different oxidation environments is calculated by using a first-principles method. The increased temperature, decreased oxygen partial pressure, and the increased charge state of O vacancy reduce the formation energy of the oxygen vacancy. The presence of V O is accompanied by a distinct redistribution of the electronic charge densities only around the Co and Si ions next to the O-vacancy site, which shows a very local influence on the host material arising from V O. Furthermore, the existence of vacancy defects ( and ) in the vicinity of the O vacancy are found to be beneficial to the formation of the O vacancy. The substitutional defects, and near the O vacancy are found to increase the formation energy of the oxygen vacancy, however, decreases the formation energy of the O vacancy.

Exploring the sensing mechanism in a dual-mode fluorescent probe responding to tryptamine and fluoride ions

The detecting mechanism in a dual-mode fluorescent probe PYNA sensing to tryptamine and fluoride ions has been explored by theoretical methods. The excited state intra-molecular proton transfer (ESIPT) process was investigated through analyzing excited hydrogen bonding changes, potential energy curves, frontier molecular orbitals and the charge density redistribution. Meanwhile, the excited state behaviors of PYNA-F, which is the product of PYNA reacting with fluoride ions, are analyzed to demonstrate the fluorescence detecting mechanism of PYNA for fluoride ions. The experimental new absorption peak of 480 nm has been assigned to the absorption of the anion form of PYNA.

Validation of crystal structure of 2‐acetamidophenyl acetate: an experimental and theoretical study

In this present study, we have determined the crystal structure of 2-acetamidophenyl acetate (2-AAPA) commonly used as influenza neuraminidase inhibitor, to analyze the polymorphism. Molecular docking and molecular dynamics have been performed for the 2-AAPA-neuraminidase complex as the ester-derived benzoic group shows several biological properties. The X-ray diffraction studies confirmed that the 2-AAPA crystals are stabilized by N–H···O type of intermolecular interactions. Possible conformers of 2-AAPA crystal structures were computationally predicted by ab initio methods and the stable crystal structure was identified. Hirshfeld surface analysis of both experimental and predicted crystal structure exhibits the intermolecular interactions associated with 2D fingerprint plots. The lowest docking score and intermolecular interactions of 2-AAPA molecule against influenza neuraminidase confirm the binding affinity of the 2-AAPA crystals. The quantum theory of atoms in molecules analysis of these intermolecular interactions was implemented to understand the charge density redistribution of the molecule in the active site of influenza neuraminidase to validate the strength of the interactions. Communicated by Ramaswamy H. Sarma

Spectroscopic Signatures of Interlayer Coupling in Janus MoSSe/MoS2 Heterostructures.

The interlayer coupling in van der Waals heterostructures governs a variety of optical and electronic properties. The intrinsic dipole moment of Janus transition metal dichalcogenides (TMDs) offers a simple and versatile approach to tune the interlayer interactions. In this work, we demonstrate how the van der Waals interlayer coupling and charge transfer of Janus MoSSe/MoS2 heterobilayers can be tuned by the twist angle and interface composition. Specifically, the Janus heterostructures with a sulfur/sulfur (S/S) interface display stronger interlayer coupling than the heterostructures with a selenium/sulfur (Se/S) interface as shown by the low-frequency Raman modes. The differences in interlayer interactions are explained by the interlayer distance computed by density-functional theory (DFT). More intriguingly, the built-in electric field contributed by the charge density redistribution and interlayer coupling also play important roles in the interfacial charge transfer. Namely, the S/S and Se/S interfaces exhibit different levels of photoluminescence (PL) quenching of MoS2 A exciton, suggesting enhanced and reduced charge transfer at the S/S and Se/S interface, respectively. Our work demonstrates how the asymmetry of Janus TMDs can be used to tailor the interfacial interactions in van der Waals heterostructures.

Isolation of Metalloid Boron Atoms in Intermetallic Carbide Boosts the Catalytic Selectivity for Electrocatalytic N2 Fixation

AbstractThe electrochemical N2 reduction reaction (eNRR) is considered to be an attractive alternative to overcome the short‐comings of the Haber‐Bosch method, where the electrocatalysts play a vital role in the eNRR efficiency. Herein, isolated single‐B sites with electron deficiency in intermetallic carbide are rationally designed to trigger charge density redistribution, achieving excellent selectivity for eNRR. The B‐rich VC nanocrystals are in situ synthesized on carbon nanofibers (B‐VC/CNFs), and the ordered intermetallic structure of VC can isolate contiguous B atoms into single‐B sites with specific electronic structures. In light of density functional theory calculations, the as‐designed BCV configuration can regulate the adsorption behavior of N2 and decrease the energy barrier for the proton–electron coupling and transferring process (*NN → *NNH), endowing the distinguished activity and selectivity, as evidenced by excellent Faradaic efficiency of 46.1% and NH3 yield of 0.443 µmol h–1 cm–2. The operando Raman spectra reveals the formation of NH intermediates on the surfaces of B‐VC/CNFs, further confirming the calculated eNRR pathway. This intermetallic carbide host strategy for generating electron‐deficient single‐B sites offers powerful guidelines for designing advanced eNRR electrocatalysts to achieve effective ammonia production.