Accumulation Of Electron Density Research Articles

Catalytic Activity and Electrochemical Stability of Ru1-xMxO2 (M = Zr, Nb, Ta): Computational and Experimental Study of the Oxygen Evolution Reaction.

We use computations and experiments to determine the effect of substituting zirconium, niobium, and tantalum within rutile RuO2 on the structure, oxygen evolution reaction (OER) mechanism and activity, and electrochemical stability. Calculated electronic structures altered by Zr, Nb, and Ta show surface regions of electron density depletion and accumulation, along with anisotropic lattice parameter shifts dependent on the substitution site, substituent, and concentration. Consistent with theory, X-ray photoelectron spectroscopy experiments show shifts in binding energies of O-2s, O-2p, and Ru-4d peaks due to the substituents. Experimentally, the substituted materials showed the presence of two phases with a majority phase that contains the metal substituent within the rutile phase and a second, smaller-percentage RuO2 phase. Our experimental analysis of OER activity shows Zr, Nb, and Ta substituents at 12.5 atom % induce lower activity relative to RuO2, which agrees with computing the average of all sites; however, Zr and Ta substitution at specific sites yields higher theoretical OER activity than RuO2, with Zr substitution suggesting an alternative OER mechanism. Metal dissolution predictions show the involvement of cooperative interactions among multiple surface sites and the electrolyte. Zr substitution at specific sites increases activation barriers for Ru dissolution, however, with Zr surface dissolution rates comparable to those of Ru. Experimental OER stability analysis shows lower Ru dissolution from synthesized RuO2 and Zr-substituted RuO2 compared to commercial RuO2 and comparable amounts of Zr and Ru dissolved from Zr-substituted RuO2, aligned with our calculations.

Steering Single-Electron Metal-Metal Bonds and Hyperfine Coupling between a Transition Metal-Lanthanide Heteronuclear Bimetal Confined in Carbon Cages.

Metal complexes bearing single-electron metal-metal bonds (SEMBs) exhibit unusual electronic structures evoking strong magnetic coupling, and such bonds can be stabilized in the form of dimetallofullerenes (di-EMFs) in which two metals are confined in a carbon cage. Up to now, only a few di-EMFs containing SEMBs are reported, which are all based on a high-symmetry icosahedral (Ih) C80 cage embedding homonuclear rare-earth bimetals, and a chemical modification of the Ih-C80 cage is required to stabilize the SEMB. Herein, by introducing 3d-block transition metal titanium (Ti) along with 4f-block lanthanum (La) into the carbon cage, we synthesized the first crystallographically characterized SEMB-containing 3d-4f heteronuclear di-EMFs based on pristine fullerene cages. Four novel La-Ti heteronuclear di-EMFs were isolated, namely, LaTi@D3h(5)-C78, LaTi@Ih(7)-C80, LaTi@D5h(6)-C80, and LaTi@C2v(9)-C82, and their molecular structures were unambiguously determined by single-crystal X-ray diffraction. Upon increasing the cage size from C78 to C82, the La-Ti distance decreases from 4.31 to 3.97 Å, affording fine-tuning of the metal-metal bonding and hyperfine coupling, as evidenced by an electron spin resonance (ESR) spectroscopic study. Density functional theory (DFT) calculations confirm the existence of SEMB in all four LaTi@C2n di-EMFs, and the accumulation of electron density between La and Ti atoms shifts gradually from the proximity of the Ti atom inside C78 to the center of the LaTi bimetal inside C82 due to the decrease of the La-Ti distance. The electronic properties of LaTi@C2n heteronuclear dimetallofullerenes differ apparently from their homonuclear La2@C2n counterparts, revealing the peculiarity of heteronuclear dimetallofullerenes with the involvement of 3d-block transition metal Ti.

Enigma of the vortex state in a strongly correlated d -wave superconductor

We show that strong electronic repulsion transforms a vortex core from a metallic type in the overdoped regime to a Mott insulator at underdoping of a strongly correlated $d$-wave superconductor. This changeover is accompanied by an accumulation of electron density at the vortex core toward local half filling in the underdoped region, which in turn facilitates the formation of the Mott-insulating core. We find that the size of vortices evolves nonmonotonically with doping. A similar nonmonotonicity of critical field ${H}_{c2}$, as extracted from superfluid stiffness, is also found. Our results explain some recent experimental puzzles of cuprate superconductors.

On the electrocatalytically active sites in graphene-based vanadium redox flow batteries

There is too much controversy and too little interdisciplinary analysis of the role of carbon electrodes in a wide range of electrochemical and electrocatalytic processes. Here we focus on vanadium redox flow batteries (VRFB), which play a central role in the transition to renewable energy sources in the electricity sector of the global economy. We used density functional theory (DFT) to determine the relationship between chemically and electrocatalytically active sites on the positive electrode and the effects of chemical surface modification that introduces a variety of oxygen functional groups. Carefully selected aromatic (Ar) model clusters were analyzed to assess the extent of the electron density accumulation on and around the free carbon sites at graphene edges. The results reveal trends that help to resolve the controversies surrounding the role of phenolic or carboxyl groups in the redox mechanism. We conclude, in agreement with other chemical and electrocatalytic reactions that involve oxygen transfer (e.g., CO2 gasification or oxygen reduction reaction), that carbene-type edge carbon atoms are responsible for VO2+ adsorption and reduction of V5+ to V4+ in VO2+. The presence of Ar-OH and Ar-COOH groups can actually inhibit the redox process as a consequence of hydrogen and/or oxygen migration to the adjacent active sites. The presence of ArO groups, while affecting the electron density at the active sites, is confirmed to have a positive effect of stabilizing the free zigzag carbon sites in a triplet ground state.

Structural and Bonding Analysis in Monomeric Actinide(IV) Oxalate from Th(IV) to Pu(IV): Comparison with the An(IV) Nitrate Series.

Single-crystal X-ray diffraction (SC-XRD) structures and Raman spectra of a series of new isomorphous molecular An(IV)-oxalate compounds (Th, U, Np, and Pu) are reported. These complexes are crystallized with cobalt(III) hexamine ([Co(NH3)6]3+) as the counter cations, [Co(NH3)6]2[An(C2O4)5]·4H2O, revealing five bidentate nonbridging oxalate ligands in the first coordination sphere (CN = 10). The nonbridging oxalate is rather uncommon for An(IV)-oxalate systems, which are widely characterized as polymeric compounds. Density functional theory (DFT) calculations were performed to examine the bonding between An(IV) cations and oxalate ligands. For comparison, we also report results obtained for the An(IV)-hexanitrate series, [(C2H5)4N]2[An(NO3)6] (with An = Th, U, Np, Pu, and Ce), which consists of O-donor ligands as well but with a larger coordination number (CN = 12). The bonding analysis confirms that the actinide-oxygen bond is predominantly ionic with a minor increase in covalency from Th to U and slight variations from U to Pu. Further comparison showed that the charge transfer increases slightly when increasing the number of anions in the coordination sphere (C2O42-: CN = 10; NO3-: CN = 12), but covalent effects as indicated by the amount of internuclear electron density accumulation are small and similar for oxalate and nitrate.

Laser induced electron drift in the magnetized quantum plasma: electron spin effects

The spin effect on accumulation of the electron density profile in the presence of an external magnetic field is investigated. In this regard, the two-fluid quantum hydrodynamic model is used to derive the interaction of intense laser light with magnetized quantum plasma. The results emphasize that the initial laser intensity and external magnetic field play significant roles in the accumulation of electron density. Moreover, the behavior of spin-up and spin-down electrons in the same spatial position is completely different. In a way, where spin-up electrons accumulate, spin-down electron density is rarefied. This fact provides a useful recipe for spintronics applications.

Weak Zinc-Zinc slipped triple bond in Zn2Li6 cluster

Weak Zn-Zn triple bond is achieved through six s1 type donors in the form of six Li atoms incorporated to Zn2 dimer which results in the formation of Zn2Li6 cluster. The proposed cluster is found to be global minimum in the potential energy surface. Accumulation of significant electron density in 4p orbitals of Zn has facilitated this bonding scenario. Various bonding analyses reveal the presence of triple bonding character and was found to be weak and slipped type. Out of the three bonds one is a conventional π bond while the other two are slipped bonds out of which one is of π type and the rest one is of σ type. The calculated thermodynamics of formation is also very favorable. The effective bond order (EBO) is calculated to be around 2.8 which also back the triple bonding nature.

Unveiling the regioselective synthesis of antiviral 5-isoxazol-5-yl-2´-deoxyuridines from the perspective of a molecular electron density theory

The regioselective synthesis of a potent antiviral sugar nucleoside isoxazole analogue in the [3+2] cycloaddition (32CA) reaction of acetonitrile- -N-oxide (ANO) and acetyl-protected 5-ethynyl-2?-deoxyuridine (EDU) has been studied at the MPWB1K/6-311G(d,p) level within perspective of the molecular electron density theory (MEDT). From an electron localization function (ELF) analysis, ANO is classified as a zwitterionic species devoid of any pseudoradical or carbenoid centre. The ortho regioisomer is energetically preferred over the meta one by the activation enthalpy of 21.7?24.3 kJ mol-1, suggesting complete regioselectivity in agreement with the experiment. The activation enthalpy increases from 53.9 kJ mol-1 in the gas phase to 71.5 kJ mol-1 in water, suggesting more facile reaction in low polar solvents. The minimal global electron density transfer (GEDT) at the TSs suggests non-polar character and the formation of new covalent bonds has not been started at the located TSs, showing non-covalent intermolecular interactions from an atoms-in- -molecules (AIM) study and in the independent gradient model (IGM) isosurfaces. The AIM analysis shows more accumulation of electron density at the C?C interacting region relative to the C?O one, and earlier C?C bond formation is predicted from a bonding evolution theory (BET) study.

Incorporation of P5+ and P3− from phosphate precursor in TiO2:P coatings produced by PEO: XPS and DFT study

The study of the incorporation of P ions in TiO2 coatings was carried out in this work using Plasma Electrolytic Oxidation (PEO) technique, which was analyzed using XPS and compared with simulations using DFT. The synthesis was carried out using the PEO technique making variations of the useful duty cycle between 10 and 50%. The solution used is composed of Na3PO4 and NaOH, with a process duration of 7 min. The TiO2/P coatings were characterized by XPS with high resolution spectra and analyzed by deconvolution of the spectra. The XPS results showed the incorporation into the crystal lattice of P ions in the form of phosphate ions [(PO4)3−] and phosphide ions (P3−). Density functional theory (DFT) calculations were carried out to demonstrate the formation of various structural defects in titanium dioxide systems. The results show the coexistence of TiO2, TiO2/PO4 and TiO2/P. In this case, the reduction of phosphorus from P5+ to P3− favors the generation of titanium phosphide (TiP) that occurs as a consequence of the high temperature generated in discharge channels (ton). Single and multiple P substitutions formation energies are presented showing that all the substitutions studied are energetically favorable. The single replacement of the P atom in TiO2 sites were calculated showing that the replacement of P at the Ti site is energetically preferred over the replacement of P at the O site with replacement energies of 0.47 eV and 1.42 eV respectively. Along the same lines, a narrowing of the band gap and a shift to the left of the states were observed in all the calculations presented due to the presence of P in the general structure. Finally, the calculation of various substitutions of P in TiO2 with the amount of P replaced in the experimental observations showed an accumulation of electron density in the energy gap attributed mainly to the orbitals of the substituted P.

Particle-in-cell Monte Carlo collision simulation and experimental measurement of Ar plasma in a fast atom beam source for surface-activated bonding

Ar plasma in a fast atom beam (FAB) source with magnetic fields, which was previously developed [Precis. Eng. 62, 106 (2020)] to achieve high-performance surface activated bonding, was analyzed by particle-in-cell-Monte Carlo collision simulation and experimental measurements. Simulation in the proposed FAB source with magnetic fields shows that higher electron density accumulation occurs near the irradiation port by E × B drift, and the potential gradient near the irradiation port steepens, which results in an increase in Ar+ flux to the irradiation port. The variation in the plasma distribution due to the effect of the magnetic field contributes to an increase in the amount of Ar-FAB irradiation, which reduces erosion of the carbon electrodes and suppresses the formation of carbon agglomerates. These simulation results were verified experimentally with Langmuir probe measurements and FAB irradiation experiments with oxide layer removal. The analysis results explain why high performance is achieved with the proposed FAB source.

Effect of Interleukin-17 gene on glomerular ultrastructure and podocyte injury in adriamycin nephropathy rat models.

The aim of this study was to investigate the mechanism of interleukin-17 (IL-17) gene in renal tissues of rats suffering from adriamycin (ADM) nephropathy and its effect on the expression level of characteristic proteins, such as Podocalyxin and Nephrin, in podocytes. Sprague-Dawley (SD) rats were randomly divided into a control group (treated with normal saline) and an ADM group (treated with adriamycin). ADM model rats were transfected with lentivirus and divided into a transfection group (transfected with recombinant plasmid IL-17-shRNA) and a negative control group (transfected with plasmid shNC). Coomassie brilliant blue G-250 (CBB) method was adopted to detect the levels of albumin in urine to validate the model. The ultrastructure of rat glomeruli was observed, and the ratio of T helper 17 cells/regulatory T cells (Th17/Treg) was measured by flow cytometry (FCM). The expression levels of IL-17, forkhead box P3 (Foxp3), Nephrin, and Podocalyxin were detected by real-time quantitative PCR (RT-qPCR) and western blot analysis. Results of the study showed that the proteinuria content of the ADM group was significantly higher than that of the control group (P<0.05). In the ADM group, the glomerular basement membrane had uneven thickness and incomplete structure, which showed foot process fusion and electron dense accumulation. However, the glomerular basal membrane in the transfected rats was thin and intact, and a small amount of epithelial foot process fusion and electron density accumulation were observed. The percentages of Th17 cells and IL-17 levels in the ADM group were significantly higher than those in the control group, while the percentages of Treg cells, Foxp3, Nephrin, and Podocalyxin levels were significantly lower than those in the control group (P<0.05). The percentages of Th17 cells, IL-17, Nephrin, and Podocalyxin in the transfection group were significantly higher than those in the ADM group and the negative control group, while the percentages of Treg cells and Foxp3 were significantly lower than those in the ADM group and the negative control group (P<0.05). The results of this study showed that abnormal activation of Th17/IL-17 cells caused podocyte injury and promoted the occurrence and progression of ADM nephropathy. In addition, inhibition of IL-17 gene expression could improve the imbalance of number of Th17 and Treg cells, which may be potentially applied in treatment of patients with primary nephrotic syndrome (PNS).

Through-Bond and Through-Space Interactions in [2,2]Cyclophanes

The interpretation of the distortions of the electron distribution in [2,2]cyclophanes (22-CPs) is controversial. Some studies indicate that there is an accumulation of electron density (ρ) outside the cavity of 22-CPs. The nature of through-space (ts) interaction is still under debate. The relative importance of ts and through-bond (tb) is an open question. In an attempt to clarify these points, we have investigated five 22-CPs and their corresponding toluene dimers by molecular orbitals analysis, electron density difference analysis, some topological analysis of ρ (quantum theory of atoms in molecules (QTAIM), electron localization function (ELF) and noncovalent interactions (NCI)), and energy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV). ρ is concentrated inside the inter-ring region. All the analyses indicated that ts is predominant. The ts is composed by attractive dispersion and Pauli repulsion, with a small covalent contribution. Except for 1 and 6, all the compounds present inter-ring bond paths.

WITHDRAWN: Hydrogen molecule detection based on Ti-embedded single vacancy defective stanene monolayer as an appropriate sensing material: A DFT study

Abstract Density functional theory calculations were carried out to investigate the interaction between hydrogen molecule and pristine/Ti-embedded defective stanene nanosheets. Ti embedding in stanene provides a satisfied surface for hydrogen molecule adsorption and sensing as can be evidenced by the enhanced adsorption energy on the Ti-embedded stanene system. The van der Waals (vdW) interactions were included to obtain the stable geometrical structures of stanene monolayers with adsorbed hydrogen molecules. Both pure and Ti-embedded stanene nanosensors exhibited semiconducting behavior as confirmed by the electronic band structure diagrams. Besides, the Ti doping provides a band gap opening for stanene at the Fermi level. The charge density difference and total electron density plots also revealed the accumulation of electron density on the adsorbed hydrogen molecule. Furthermore, there are electron depletion between the hydrogen molecule and stanene nanosheet, indicating the weak physical interaction between them. The work function was slightly reduced after doping of Ti atom, as well as the binding of hydrogen molecules on the Ti-embedded stanene sensors. The calculated recovery time values showed the unique reusability of the stanene based hydrogen molecule sensors. These insights would be quite relevant to the rational design of novel Ti-embedded stanene based sensors for hydrogen molecule detection.

The role of the natural transition orbital density in the S0 → S1 and S0 → S2 transitions of fulvene with next generation QTAIM

We present, for the first time, the S0 → S1 (S01) and S0 → S2 (S02) natural transition orbital (NTO) densities for fulvene, using the 3-D next generation QTAIM that can visualize and quantify the rearrangement of the charge density that occurs in response to the applied torsion and as a consequence of the preferred direction of electron density accumulation. A symmetrization of the position of the bond critical point (BCP) of the torsional C2-C6 BCP along the containing bond-path was determined to be characteristic of the presence of a conical intersection (CI) for the S0 → S1 (S01) transition.

First-Principles Insights into the Interface Chemistry between 4-Aminothiophenol and Zinc Phosphide (Zn3P2) Nanoparticles.

Accurate prediction of the structures, stabilities, and electronic structures of hybrid inorganic/organic systems is an essential prerequisite for tuning their electronic properties and functions. Herein, the interface chemistry between the 4-aminothiophenol (4ATP) molecule and the (001), (101), and (110) surfaces of zinc phosphide (Zn3P2) has been investigated by means of first-principles density functional theory calculation with a correction for van der Waals interactions. In particular, the atomic-level insights into the fundamental aspects of the 4ATP adsorption, including the lowest-energy adsorption configurations, binding energetics, structural parameters, and electronic properties are presented and discussed. The 4ATP molecule is demonstrated to bind most strongly onto the least stable Zn3P2(001) surface (Eads = −1.91 eV) and least strongly onto the most stable Zn3P2(101) surface (Eads = −1.21 eV). Partial density of states analysis shows that the adsorption of 4ATP on the Zn3P2 surfaces is characterized by strong hybridization between the molecule’s sulfur and nitrogen p-orbitals and the d-orbitals of the interacting surface Zn ions, which gave rise to electron density accumulation around the centers of the newly formed Zn–S and Zn–N chemical bonds. The thermodynamic crystal morphology of the nonfunctionalized and 4ATP-functionalized Zn3P2 nanoparticles was obtained using Wulff construction based on the calculated surface energies. The stronger binding of the 4ATP molecule onto the less stable (001) and (110) surfaces in preference to the most stable (101) facet resulted in the modulation of the Zn3P2 nanocrystal shape, with the reactive (001) and (110) surfaces becoming more pronounced in the equilibrium morphology.

A detailed look at the bonding interactions in the microsolvation of monoatomic cations.

Global and local descriptors of the properties of intermolecular bonding, formally derived from independent methodologies (QTAIM, NCI, NBO, density differences) afford a highly complex picture of the bonding interactions responsible for microsolvation of monoatomic cations. In all cases, the dominant factor dictating geometries and interaction strengths is the electrophilic power of the metal cation. The formal charge disrupts the hydrogen bonding network otherwise present in pristine water clusters, making the hydrogen bonds considerably stronger, even inducing some degree of covalency. All MO interactions are highly ionic, with strengths than in some cases approach that of the reference LiCl bond. Accumulation of electron density in the region connecting MO is observed, thus, ionic bonding in the microsolvation of monoatomic cations is not as simple as an electrostatic interaction between opposing charges.

RETRACTED: Tuning the structural and electronic properties of Ag/Au embedded arsenene monolayers and investigation of their adsorption behaviors for various gas molecules

Abstract Motivated by the large number of studies on nanoelectronic and optoelectronic applications of two-dimensional materials, we investigated the structural and electronic properties of Ag and Au-embedded arsenene monolayers, and then examined the interaction of various gas molecules with theses doped structures. The results of adsorption energies indicate that the embedding of Ag and Au atoms into the structure of arsenene is energetically stable. Various adsorption sites of gas molecules on the considered Ag and Au-embedded arsenene nanosheets were examined in this work. The charge accumulation between the Ag/Au and As atoms is an indication of the formation of covalent bonds between these two atoms. Besides, the charge density difference plots show the electron density accumulation on the adsorbed gas molecules. There are large overlaps between the projected density of states of the interacting atoms, suggesting the covalent nature of interaction between them.

Rationalizing the stability and interactions of 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidin-1-ium 2-hydroxy-3,5-dinitrobenzoate salt

The crystal structure of the salt produced by the reaction of pyrimethamine (an antimalarial drug) with 2-hydroxy-3,5-dinitrobenzoic acid [systematic name: 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidin-1-ium 2-hydroxy-3,5-dinitrobenzoate] has been investigated using X-rays diffraction data collected at room temperature. The results showed that there are strong intermolecular C–H⋯O, N–H⋯N, O–H⋯O types of hydrogen bonding interactions that play a key role in the crystal structure stabilization while C–H⋯O and C–H … π interaction further stabilize the structure. In addition, theoretical calculations were done to compute the binding free energies and the electron densities associated to heterodimeric, heterotrimeric and heterotetrameric salt assemblies of the pyrimethamine-2-hydroxy-3,5-dinitrobenzoate salt. The molecular electron densities, electrostatic potential and the regions of electron density accumulation as well as depletion were explored for these assemblies. These analyses not only suggest the high salt stability but also appropriate electrostatic properties of the pyrimethamine drug for the interaction with a carboxylic group that is attached to the side chains of glutamate and aspartate residues in proteins.

Hydrazine adsorption on perfect and defective fcc nickel (100), (110) and (111) surfaces: A dispersion corrected DFT-D2 study

We present density functional theory calculations, with a correction for the long-range interactions, of the adsorption of hydrazine (N2H4) on the Ni (110), (100), and (111) surfaces, both defect-free planes and surfaces containing point defects in the form of adatoms and vacancies. Several low-energy adsorption structures for hydrazine on the perfect and defective surfaces have been identified and compared. The hydrazine molecule is shown to interact with the Ni surfaces mainly through the lone-pair of electrons located on the N atoms, forming either monodentate or bidentate bonds with the surface. The strength of N2H4 adsorption on the perfect surfaces is found to be directly related to their stability, i.e. it adsorbs most strongly onto the least stable (110) surface via both N atoms in a gauche-bridge configuration (Eads = −1.43 eV), followed by adsorption on the (100) where it also binds in gauche-bridge configurations (Eads = −1.27 eV), and most weakly onto the most stable (111) surface via one N–Ni bond in a trans-atop configuration (Eads = −1.18 eV). The creation of defects in the form of Ni adatoms and vacancies provides lower-coordinated Ni sites, allowing stronger hydrazine adsorption. Analysis into the bonding nature of N2H4 onto the Ni surfaces reveals that the adsorption is characterized by strong hybridization between the surface Ni d-states and the N p-orbitals, which is corroborated by electron density accumulation within the newly formed N–Ni bonding regions.

The 3-D bonding morphology of the infra-red active normal modes of benzene

We present for the first time a visualization of the 3-D morphology of all the CC and CH bonds for the relaxed structures as well as four infra-red (IR) active normal modes of benzene using the complete bond-path framework set B = {p,q,r} a vector-based interpretation of the chemical bond within the QTAIM framework. The bond-path framework set B = {p,q,r} comprises three strands in the ground state, with the r-path corresponding to the familiar QTAIM bond-path. The new p- and q-paths are formulated from the least and most preferred directions of electron density accumulation respectively.