Amount Of Charge Transfer Research Articles

Modifying the sensibility of nonmetal-doped phosphorene by local or global properties

Doping heteroatoms into phosphorene has attracted considerable attention due to its effectiveness in enhancing the stability and tailoring the electronic properties as well as sensing capability. In this work, we performed a density functional theory (DFT) calculation to study the effect of nonmetallic heteroatom dopants (X, X = Be, B, C, N, O, S, Se, Te, F, Cl, Br and I) on the stability and sensibility of X-doped phosphorene. We found that phosphorene structures doped with the 2nd period and VIA group atoms possess relatively high internal stability due to the effective X-P bonding. More interestingly, the interaction between P sites and small species can be modified effectively by a local property-the charge (Q) of P sites-and/or a global property-the Fermi level (EFermi) of X-doped phosphorene-depending on the charge transfer degree between the species and the P sites. For the species with dramatic charge transfer, the local Q of the P site plays the most important role. For the species with moderate charge transfer, the major determinant of sensibility is the local Q and global EFermi. This work reveals the relation between the properties of X-doped phosphorene and the physico-chemical parameters of X, including the electronegativity, atomic number, and X-P bonding strength, and provides a useful guideline for choosing the appropriate nonmetallic dopants to enhance the stability and sensibility of X-doped phosphorene towards special species.

Fast Charging of Li-Ion Cells: Part III. Relaxation Dynamics and Trap-Controlled Lithium Ion Transport

Fast charging of Li-ion batteries would ease consumer concerns regarding refueling time of electric vehicles. In this series of articles, we are systematically examining the effects of high currents flowing through the cell. Here we consider open-circuit relaxation dynamics for cell voltage and individual electrode potentials after abrupt termination of steady-state charging currents (1-6C) or short current pulses (< 30 s) of either polarity (to 16C). We demonstrate that dispersive kinetics observed after these current perturbations become faster for higher currents applied before the rest period. Our observations indicate that the voltage relaxation behaviors (i) depend on the current during charge, and less so on the state of charge, (ii) display universal stretched-exponential kinetics, (iii) can be induced by a short current pulse, (iv) require a minimum amount of charge transfer during the pulse, and (v) originate mainly from the oxide cathode. Trap controlled Li+ ion transport through a partially disordered oxygen-depleted subsurface layer in the cathode is suggested as a possible origin for the relaxation behavior. The slow multidecadal responses to high currents can cause the nonlinearities observed during rapid charging of the electrochemical cells, reported in Part 2 of this series.

Boosting the photocatalytic oxidative desulfurization of dibenzothiophene by decoration of MWO4 (M=Cu, Zn, Ni) on WO3

The surface of WO3 was partially decorated with transition metal tungstate MWO4 (M = Cu, Zn, Ni) using impregnation method followed by solid-state reaction. It is found that MWO4/WO3 photocatalysts showed a higher activity for photocatalytic oxidative desulfurization (PODS) of dibenzothiophene (DBT) than pure WO3 or MWO4 under visible light irradiation. Moreover, the activity for PODS of DBT on MWO4/WO3 depends on the content of MWO4 decoration on WO3 surfaces. 0.2% CuWO4/WO3, 1% ZnWO4/WO3, and 0.5% NiWO4/WO3 exhibited the highest activity among CuWO4/WO3, ZnWO4/WO3 and NiWO4/WO3 samples. However, as compared with 1% ZnWO4/WO3 and 0.5% NiWO4/WO3, the 0.2% CuWO4/WO3 sample exhibited superior visible light photocatalytic activity for DBT conversion. Brunauer-Emmett-Teller method (BET), SEM, and ultraviolet-visible diffuse reflectance spectra (UV–vis DRS), high resolution transmission electron microscope (HRTEM), photoluminescence spectroscopy (PL), and a series of titration experiments were used to seek the reason for the positive impact of MWO4 on the photocatalytic activity of WO3. As compared with pure WO3, no notable changes of specific surface areas, morphologies, and light absorption are observed after MWO4 (M = Cu, Zn, Ni) decoration. The formation of heterojunction structure between MWO4 and WO3, which promotes charge separation efficiency, was the main reason for the high photocatalytic activity of MWO4/WO3 photocatalyst. Moreover, difference in PODS activity between MWO4/WO3 heterojunctions is proved to be affected by their charge separation and transfer efficiency and amount of active species.

Interaction of gold clusters with graphene and graphene layer over [formula omitted] surface: A density functional study

Heterogeneous catalysis on support stabilized metal clusters has shown significant progress in the past decade. In order to unravel the effect of neutral support on the growth motif of small clusters, here we report structural and electronic properties of Aun(n=2,6,and8) clusters deposited on Ni(111) supported graphene sheet using the spin-polarized version of the plane wave based pseudo-potential method. In general, the trend in the growth pattern shows that all deposited Aun clusters favor planar configurations, similar to that in the isolated case. More importantly, the binding energy of the Aun clusters on graphene increases with the Ni support, which is an important outcome as it can be realized that the Ni(111) support indeed helps in stabilizing the Aun clusters on the graphene, avoiding them from aggregating, a common problem in heterogeneous catalysis. A finite amount of overall charge transfer from the substrate to the deposited cluster was observed with a charge accumulation of 0.44e in case of Au8 which can play a significant role for enhancing its catalytic performance. From the density of states it was revealed that the energy states form Au8 cluster contributed to the fermi energy level of the Au8-Ni111-graphene, suggesting a possible reactivity of this cluster.

Directional affinity of a spherical Gold nanoparticle for the adsorption of DNA bases.

In this work, the adsorption activities of different facets of a spherical gold nanoparticle (Au(111), Au(100) and Au(110)) for adenine (ADE) and cytosine (CYT) in two different environments including gas phase and in the presence of solvent (water) have been investigated, separately. It has been found that the adsorption energy (Ead) and geometry of the DNA bases depend strongly on the kind of nanoparticle facet. The Au (110) facet showed the highest adsorption affinity for the ADE and CYT in both gas phase and water compared to Au(111) and Au(100) facets. Comparison of the Eads of bases calculated in the gas phase with those obtained in the presence of water showed that the electrostatic field of solvent decreases the Eads of bases, especially, for the Au (110) facet. The adsorption geometry of the CYT showed strong dependency on the kind of nanoparticle facet compared to ADE. Also, it has been shown that the direction and amount of charge transfer (CT) between the molecule and nanoparticle strongly depends on the kind of nanoparticle facet and environment. The CT is from the Au (111) facet to the ADE while the CT direction is reversed when the ADE is adsorbed on the Au (110) and Au (100) facets in the gas phase. The CT is from the CYT to three facets in the gas phase while its direction for the ADE and CYT adsorbed on Au (100) facet is reversed. The atoms in molecules (AIM) analysis has been employed to determine the bond paths (BPs) and bond critical points (BCPs) between the bases and facets. The infrared (IR) spectra of the bases adsorbed on the selected facets were calculated and compared with each other and with the spectra of the isolated bases. It was found that the symmetric and unsymmetric stretching of the NH of NH2 group, C-H stretching of the rings and CO stretching of bases can be used for the discrimination of the selected facets.

Role of Oxygen Vacancies on Oxygen Evolution Reaction Activity: β-Ga2O3as a Case Study

Neutral oxygen vacancies (Ovʼs) in semiconductor oxides give rise to excess electrons that have the potential to affect the binding of adsorbates to the surface through surface-to-adsorbate charge transfer, and, as a result, to alter the overpotential (OP) of reactions on oxygen-deficient materials compared to stoichiometric materials. We report a systematic computational investigation of the effects of Ovʼs on the oxygen evolution reaction (OER) overpotential for β-Ga2O3, a d10 semiconductor that has been shown to exhibit high activity for water splitting. We investigated 18 β-Ga2O3 surfaces/slabs, with and without Ovʼs and observed a clear dependence of OER activity on Ovʼs. A general finding emerged that the excess electrons associated with Ovʼs are found to participate in charge transfer to OER intermediates, making their bonds to the surface more ionic and stronger, depending on the amount of charge transfer. The OER reaction step free energies are significantly affected and the ensuing overpotential...

Study of solvent effect on thermodynamic stability and electron efficiency of MZ-341 dye

Photo physical and thermodynamic properties of D-π-A organic dye, MZ-341(4-[4-(diphenylamino)phenyl]-7-oxo-7Hbenzimidazo[2,1-a]benzo[de]isoquinoline-11-carboxylic acid), have been investigated for ground and excited states, in order to indicate the different effects of solvent on it as an organic sensitizer in Dye-sensitized Solar Cells (DSSCs). Calculations were performed with Density functional theory approach (DFT) and Time-dependent Density functional theory (TD-DFT) in three different solvents, including water, acetonitrile and carbon tetrachloride. In this work solvation free energy, electron transfer during excitation, Q factor, dipole moment, electronic absorption spectra, recombination (ability of charge injection), life time of excited states, intramolecular bond lengths, light harvesting energy (LHE) by dye and exciton binding energy (EBE) were investigated for ground and excited states. The analysis indicates that amount of intramolecular charge transfer is less in more polar solvents than other solvents. Due to the change in charge distribution during excitation, changes in the value and orientation of the dipole moment and Q factor are generated so it is recognized in more polar solvents; dipole moment and Q factor are higher. Our results showed that solvent also have effect on solvation free energy parameter (ΔG solvation) and consequently the stability of dye so it has been investigated that acetonitrile is the best solvent for use with MZ-341 dye due to the electron and thermodynamic properties.

Benzofuropyridine-Based Highly Efficient Thermally Activated Delayed Fluorescence Emitters.

Novel thermally activated delayed fluorescence (TADF) materials with benzofuro[2,3-b]pyridine (BFPd) as an electron acceptor and carbazole derivatives [carbazole (Cz), 1,3,6,8-tetramethyl-9H-carbazole (tmCz), and 9'H-9,3':6',9''-tercarbazole (terCz)] as electron donors are designed, and their electronic and optical properties are investigated theoretically for a deep blue organic light-emitting diode (OLED). We obtain the energies of the first singlet (S1) and first triplet (T1) excited states of TADF materials by performing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the ground state by using the dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. We show that terCz-BFPd would be a suitable blue OLED emitter because it has sufficiently small ΔEST value (0.048 eV), which is favorable for a reverse intersystem crossing process from the T1 to S1 states and an emission wavelength of 432.8 nm with sufficiently large oscillator strength (F) value.

Gas-sensing properties of armchair silicene nanoribbons towards carbon-based gases with single-molecule resolution

Using non-equilibrium Green’s function (NEGF) formalism combined with first-principle density functional theory (DFT), we explore the nature of adsorption of carbon-based gases and the resulting structural, electronic (band structure, density of states, Mulliken population, and electron density), and transport properties (current-voltage characteristics and transmission eigenstates) on pure and defected armchair silicene nanoribbons (ASiNRs) for sensing applications. It is observed that CH4 and CO2 are weakly adsorbed on pristine (P-ASiNR) as well as defective (D-ASiNR) nanoribbons owing to their low adsorption energy and charge transfer, thereby exhibiting low sensitivity and high recoverability. On the other hand, CO is chemisorbed on both nanoribbons exhibiting greater adsorption energy and current, thereby having more sensitivity and more recovery time. Mulliken population analysis reports that a significant amount of charge transfer prevails between ASiNR and gas molecules, validating our results for adsorption energies of the systems. CO2 and CO donates charge to the ASiNR, showcasing their electron-donating nature; contrariwise, CH4 behaves as electron-withdrawing gas by accepting electronic charge from ASiNRs. Our calculations reveal that introduction of vacancy defect increases the sensitivity significantly which is promising for future gas-sensing applications as well.

Computational and Experimental FT‐ IR, NMR, UV‐Vis Spectral Studies of 5,5′‐((4‐chlorophenyl)methylene)bis(1,3‐dimethyl‐6‐(methylamino)pyrimidine‐2,4(1H,3H)‐dione)

AbstractSynthesis of a novel 5,5′‐((4‐chlorophenyl)methylene)bis(1,3‐dimethyl‐6‐(methylamino)pyrimidine‐2,4(1H,3H)‐dione) has been done, followed by respective characterization by various spectroscopic techniques viz FT‐IR, 1H‐NMR, 13C‐NMR, UV‐Vis spectroscopy and computational methods. The study of the structure was done by Density Functional Theory (DFT) at the theory level Becke3–Lee–Yang–Parr (B3LYP) functional and 6–31G (d, p) as basis set. A close examination of various structural and thermodynamic parameters, electrostatic potential, electrophilicity (ω), chemical potential (μ), chemical hardness (η) and max amount of electronic charge transfer (▵Nmax) was done for this compound. Natural bond orbital analysis was employed to study the hyper conjugative interactions occurring within the molecule that are responsible for the stability of the molecule. To study the chemically active sites in the molecule, local reactivity descriptors were also calculated. Electric dipole moment, polarizability and first static hyperpolarizability values have been investigated for the title compound. In addition to it, a discussion about correlation graphs between 1H‐NMR and 13C‐NMR spectroscopic values is also done.

Theoretical Mechanistic Study of Nickel(0)/Lewis Acid Catalyzed Polyfluoroarylcyanation of Alkynes: Origin of Selectivity for C–CN Bond Activation

The cooperative mechanism of Ni(0)/Lewis acid catalyzed carbocyanation of alkyne with 2,3,5,6-tetrafluorobenzonitrile was investigated using the DFT method. Our calculations indicate that the most feasible catalytic cycle consists of the oxidative addition of a C–CN bond to the Ni(0) center, alkyne insertion into the C(aryl)–Ni(II) bond, and reductive elimination. Notably, the Lewis acid (LA) interacting with the cyano nitrogen atom of the substrate can have a significant effect on activating the C–CN bond while suppressing C–H and C–F bond activations. The origin of lower C–CN activation barrier in the presence of LA can be attributed to the remarkably enhanced charge transfer (CT) amount from the Nicat 3d orbital to C-CN σ* + π* antibonding molecular orbital and the little decrease of interaction energy between Ni-catalyst and substrate. In the C–F and C–H bond activations in the presence of LA, on the contrary, the significant decrease of interaction energy between Ni-catalyst and substrate and almost ...

The role of interface charge transfer on Pt based catalysts for water splitting

The controllable charge transfer at the interface between substrate and supported metal provides a powerful tool for fine tuning the electronic structure and catalytic activity of supported metal. Aiming at exploring the role of interface charge transfer in cleavage of OH bond in H2O, we performed DFT calculations to investigate H2O splitting on Pt based catalysts: Starting from supported Pt, going to TM13@Pt42 nanoparticles. By choosing different substrates or introducing different electronegative dopants, the amount of charge transfer from Pt can be manipulated. It was found that the charge transfer from Pt to substrate and core metals to shell Pt will influence the ability of Pt atoms to cleavage the OH bonds. Our work reveals that the interface charge transfer can act as one of the microscopic driving forces for the OH bonds cleavage, which will provide useful insight into rational design catalysts for H2O splitting.

Solvent effects and charge transfer states in organic photovoltaics: a time-dependent density functional theory study on the PCPDTBT:PCBM low band gap system

Long-range corrected time-dependent density functional theory has been used to study the solvent effect on excited state properties of PCPDTBT:PCBM (Poly[2,6-(4,4-dimethyl-4H-cyclopenta[2,1-b:3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)]:[6,6]-Phenyl-C61-butyric acid methyl ester) molecular system. A polarizable continuum model has been applied within the linear response (LR) and state-specific (SS) approaches to account for the dielectric environment. The results show that the influence of the solvent depends on the nature of the excitations. For neutral excitonic states that are essentially localized on a single molecule, the solvent has little or no effects on the excitation energies according to both solvent schemes. On the other hand, for states with a significant amount of charge transfer (CT), the SS approach predicts a sufficient decline in the excitation energy as the dielectric constant increases so that the CT state can be stabilized to the lowest excited state, whereas the LR counterpart shows almost no change. The comparison of two solvent approaches is discussed.

Tunable phase stability and contact resistance of monolayer transition metal dichalcogenides contacts with metal

Monolayer transition metal dichalcogenides/metal (MX2/metal) based transistors have been widely studied. However, further development is hindered by the large contact resistance between MX2 and metal contact. In this paper, we demonstrated that interfacial charge transfer between MX2 and metal is the key for tuning contact resistance. With the lattice misfit criterion applied to screen combination of MX2s and metals, it has been found out that both phase stability of MX2 and contact nature between MX2 and metal will be sensitively affected by interfacial charge transfer. Additionally, we have identified seven MX2/metal systems that can potentially form zero Schottky barrier contacts utilizing phase engineering. On base of interfacial charge calculations and contact resistance analysis, we have presented three types of MX2/metal contacts that can be formed with distinguished contact resistance. Our theoretical results not only demonstrate various choice of MX2/metal designs in order to achieve different amounts of interfacial charge transfer as well as manipulate contact resistance, but also shed light on designing ohmic contacts in MX2/metal systems.

Quantum mechanical effects in zwitterionic amino acids: The case of proline, hydroxyproline, and alanine in water.

In this work, we use ab initio molecular dynamics simulations to elucidate the electronic properties of three hydrated zwitterionic amino acids, namely proline, hydroxyproline, and alanine, the former two forming an important constituent of collagen. In all three systems, we find a substantial amount of charge transfer between the amino acids and surrounding solvent, which, rather surprisingly, also involves the reorganization of electron density near the hydrophobic non-polar groups. Water around proline appears to be slightly more polarized, as reflected by the enhanced water dipole moment in its hydration shell. This observation is also complemented by an examination of the IR spectra of the three systems where there is a subtle red and blue shift in the O-H stretch and bend regions, respectively, for proline. We show that polarizability of these amino acids as revealed by a dipole moment analysis involves a significant enhancement from the solvent and that this also involves non-polar groups. Our results suggest that quantum mechanical effects are likely to be important in understanding the coupling between biomolecules and water in general and in hydrophobic interactions.

Insights into the mechanism of metal-polymer contact electrification for triboelectric nanogenerator via first-principles investigations

Surface micro/nano structures and materials modification are the major methods to enhance the output performance of triboelectric nanogenerator (TENG). However, the microcosmic mechanism on how they take effect has not been clear yet. Herein, the typical material pair Al-PTFE of TENG is taken as the example to study the mechanism of metal-polymer contact electrification via first-principles investigations and provide theoretical basis for the optimized design of TENG.We demonstrate that the interface barrier of the contact materials is the more fundamental parameter related to contact electrification, rather than the effective work function difference which has been thought to be proportional to the amount of charge transfer. The relationship between charge transfer and interface distance is also investigated. We confirm that charge transfer is significantly affected by the stress on the contact region, and it can even occur without contact. Based on the results, we propose that the surface micro/nano structures design on TENG should aim at making the contact regions in an appropriate stress state instead of only increasing the contact area, and improving the specific surface areas in the effective range of contact electrification via nanostructures for generating extra charge transfer freely.In order to provide theoretical basis for surface modification on contact materials which has been little studied, the direction, driving force and the intrinsic cause of charge transfer are investigated. It is demonstrated that the electrons acceptor is the LUMO (lowest unoccupied molecular orbital) on PTFE surface, and the driving force of charge transfer is the electrostatic attraction generated by the electrons acceptor. In addition, the key role and intrinsic mechanism of the interface chemical bond in PTFE is studied. We propose that the fundamental goal of chemical modification on contact materials should be to lower the LUMO energy level on the surface of electron acceptor materials.

Effect of anti-site point defects on the mechanical and thermodynamic properties of MgZn2, MgCu2 Laves phases: A first-principle study

A theoretical investigation on the effect of anti-site point defects on mechanical and thermodynamic properties of MgZn2 and MgCu2 based on the first-principles calculations has been implemented. The results show that Mg anti-site defect on Zn or Cu site plays a reinforcing role, while exhibiting a more brittle behavior. However, the defect phase of Cu anti-sites on Mg sublattice shows a ductile tendency. The temperature-dependent thermodynamic properties are also predicted along with Debye-Grüneisen model including Debye temperature, thermal expansion coefficient and vibrational heat capacity as well as vibrational entropy. Taking into account the contribution of the lattice vibration and thermal electronic excitations, the Helmholtz free energy F can be calculated, suggests that anti-site defects caused by the occupancy of Mg at the Zn or Cu site are thermodynamically unstable compared to the defect-free phases. In addition, the total amount of charge transfer, the overall and the local difference charge densities are further discussed to analyze the mechanism of mechanical properties.

Synthesis [1-(4-acetylphenyl)-3-(2-methylphenyl)]triazene: NMR, Vibrational, X-ray Crystallography Characterization with HF/DFT Studies

[1-(4-acetylphenyl)-3-(2-methylphenyl)]triazene (AMT) was synthesized by experimental methods, its chemical and spectrometric properties was studied by FT-IR, FT-Raman,1H-NMR,13C-NMR and X-ray singlecrystal diffraction methods. The obtained results showed that this structure hasorthorombic system with space group of pbca and eight molecules in unit cell. Its unit cell parameters comprise a=8.0665(2), b=8.0019(2) and c=21.5249(5). Then molecular number of [1-(4-acetylphenyl)-3-(2-methylphenyl)]triazene (AMT) structure has been studied by HF/DFT methods. However, FT-IR, FT-Raman,1H-NMR, 13C-NMR spectra were analyzed that the obtained results for vibrational spectra and amount of chemical shift correspond significantly with theoretical methods. Some structural parameters such as bonds length, bonds angle and dihedral angle were studied using theoretical and experimental methods. The parameters such as thermodynamical parameters, dipole moment, HOMO and LUMO energetic values, electrophilicity (ω), chemical potential(μ), chemical hardness(η) and max amount of electronic charge transfer (ΔNmax) are calculated for this compound in conclusion. The proposed methods were successfully applied to the determination of vibrational spectra, chemical shift amounts and structural parameters.

Tuning charge transfer in the LaTiO3/RO/LaNiO3 (R = rare-earth) superlattices by the rare-earth oxides interfaces from a first-principles calculation

We investigate the internal charge transfer at the isopolar interfaces in LaTiO3/RO/LaNiO3 (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) superlattices by means of density functional theory calculations. The charge transfer from Ti sites to Ni sites in all superlattices is induced by the electronegativity difference between the elements Ti and Ni, and the lanthanide oxides interfaces can modulate the amount of charge transfer. Comparison of the perovskite heterostructures with the different rare-earth interfaces shows that increasing the deviations of bond angles from 180.0° and the oxygen motions near the interfaces enhance charge transfer. The 4f electrons themselves of rare-earth elements have faint influences on charge transfer. In addition, the reasons why our calculated 4f states of Sm and Tm elements disagree with the experimental systems have been provided. It is hoped that all the calculated results could be used to design new functional nanoelectronic devices in perovskite oxides.

DFT studies on interaction between bimetallic [Au 2 M] clusters and cellobiose

Abstract The interactions of cellobiose with [Au2M] clusters have been studied using density functional theoretical methods. The computed Donor-Acceptor Map (DAM) analyses provide evidence for the electron donating and accepting nature of the cellobiose, [Au2M] clusters respectively. The electronic structural studies indicate that metal clusters bind with conformers of cellobiose through oxygen atom of the glycosidic bond or other hydroxyl groups. The presence of negative binding energy shows the strong bonding between the cluster and CB, where [Au2Cu] interact more efficiently than [Au3] and [Au2Ag] in a bare form. The introduction of positive charge via ionization increases the binding energy of all the systems. Further halogen and PH3 ligands in the passivation layer of the [Au2M] clusters enhance their interaction with cellobiose. The amount of charge transfer exhibited by the metal cluster after bonding with cellobiose weakens the glycosidic bond, which is reflected in the structural parameters, DAM and partial Mulliken charge values. The computed results propose that [Au2CuFPH3] cluster is binding strongly to cellobiose conformers compared to other clusters studied.