Bonding charge density from atomic perturbations

Charge transfer among individual atoms is the key concept in modern electronic theory of chemical bonding. In this work, we present a first‐principles approach to calculating the charge transfer. Based on the effects of perturbations of an individual atom or a group of atoms on the electron charge density, we determine unambiguously the amount of electron charge associated with a particular atom or a group of atoms. We computed the topological electron loss versus gain using ethylene, graphene, MgO, and SrTiO₃ as examples. Our results verify the nature of chemical bonds in these materials at the atomic level. © 2015 Wiley Periodicals, Inc.     

Direct visual evidence for chemical mechanism of SERRS of pyrazine adsorbed on Ag nanoparticle via charge transfer

In this paper, the chemical enhancement of surface-enhanced resonance Raman scattering (SERRS) of pyrazine adsorbed on Ag nanoparticles through charge transfer was experimentally and theoretically investigated. Based on the calculations by density functional theory (DFT) and time-dependent DFT (TD-DFT), we theoretically analyzed the absorption spectra and SERS spectrum of the S-complex of pyrazine–Ag₂₀. The charge transfer in the process of resonant electronic transitions between adsorbed molecule and metal cluster can be visualized by the method of charge difference density. It is a direct evidence for the chemical enhancement mechanism of SERRS of pyrazine molecule adsorbed on Ag nanoparticle via charge transfer between molecule and metal. Additionally, the intracluster charge redistribution was also considered as an evidence for the electromagnetic enhancement. By comparing the experimental and theoretical results, it was demonstrated that the SERRS of the pyrazine molecule absorbed on silver clusters in different incident wavelength regions is dominated by different enhancement mechanisms via the chemical and electromagnetic enhancements.     

有机半导体材料中的电荷转移

在介绍有机半导体材料电荷转移基本理论的基础上,对利用电荷转移研究有机半导体材料的导电、光电导和发光过程的现状进行评述,认为电荷转移是有机半导体材料研究的关键问题,开展其研究不仅有助于弄清一些新现象、新效应的物理起因,还可望找到预测有机半导体材料相关性能的有效手段.     

Determination of the Degree of Charge‐Transfer Contributions to Surface‐Enhanced Raman Spectroscopy

We explore the application of a previously suggested formula for determining the degree of charge transfer in surface‐enhanced Raman scattering (SERS). SERS is often described as a phenomenon which obtains its enhancement from three major sources, namely the surface plasmon resonance, charge‐transfer resonances as well as possible molecular resonances. At any chosen excitation wavelength, it is possible to obtain contributions from several sources and this has led to considerable confusion. The formula for the degree of charge transfer enables one to separate these effects, but it requires that spectra be obtained either at two or more different excitation wavelengths or as a function of applied potential. We apply this formula to several examples, which display rather large charge‐transfer contributions to the spectrum. These are p‐aminothiophenol (PATP), tetracyano‐ ethylene (TCNE) and piperidine. In PATP we can show that several lines of the same symmetry give the same degree of charge transfer. In TCNE we are able to identify the charge‐transfer transition, which contributes to the effect, and are able to independently determine the degree of charge transfer by wavenumber shifts. This enables a comparison of the two techniques of measurement. In piperidine, we present an example of molecule to metal charge transfer and show that our definition of charge transfer is independent of direction.     

Charge transfer in organic molecules for solar cells: theoretical perspective

This tutorial review primarily illustrates rate theories for charge transfer and separation in organic molecules for solar cells. Starting from the Fermi's golden rule for weak electronic coupling, we display the microcanonical and canonical rates, as well as the relationship with the Marcus formula. The fluctuation effect of bridges on the rate is further emphasized. Then, several rate approaches beyond the perturbation limit are revealed. Finally, we discuss the electronic structure theory for calculations of the electronic coupling and reorganization energy that are two key parameters in charge transfer, and show several applications.     

Strong localization of positive charge in DNA induced by its interaction with environment

We investigate a quantum state of positive charge in DNA. A quantum state of electron hole is determined by the competition of the pi-stacking interaction b sharing a charge between different base pairs and the interaction lambda with the local environment which attempts to trap charge. To determine which interaction dominates, we investigate charge quantum states in various (GC)(n) sequences choosing DNA parameters that satisfy experimental data for the balance of charge transfer rates G(+) <--> G(n)(+), n = 2, 3. We show that experimental data can be consistent with theory only assuming b G(n)(+), n > or = 4 and comparing the experimental results with our predictions.     

Signature OH absorption spectrum from cluster models of solvation: a solvent-to-solute charge transfer state

Ab initio electronic structure theory calculations on cluster models support the characterization of the signature absorption spectrum of a solvated hydroxyl OH radical as a solvent-to-solute charge transfer state modulated by the hydrogen-bonding environment. Vertical excited states in OH(H2O)n clusters (n = 0-7, 16) calculated at the TDDFT level of theory (with companion calculations at the EOM-CCSD level of theory for n 相似文献   

Theory and simulation of charge transfer through DNA – nanotube contacts

We address the problem of charge transfer between a single-stranded adenine oligomer and semiconducting boron nitride nanotubes from a theoretical and numerical perspective. The model structures have been motivated by computer simulations; sample geometries are used as the input of an electronic structure theory that is based upon an extended Su-Schrieffer-Heeger Hamiltonian. By analyzing the emerging potential energy surfaces, we obtain hole transfer rates via Marcus’ theory of charge transfer. In the presence of nanotubes, these rates exceed those of isolated DNA single strands by a factor of up to 10⁴. This enhancement can be rationalized and quantified as a combination of a template effect and the participation of the tube within a superexchange mechanism.     

Photoinduced Intramolecular Charge Transfer in Donor-acceptor Dyad and Donor-bridge-acceptor Triad

The ground and excited state properties of the 60fullerene, diphenylbenzothiadiazole-triphenylamine (PBTDP-TPA) dyad and fullerene-diphenylbenzothiadiazole-triphenylamine (fullerene-PBTDP-TPA) triad were investigated theoretically using density functional theory with B3LYP functional and 3-21G basis et and time-dependent density functional theory with B3LYP functional and STO-3G basis set as well as 2D and 3D real space analysis methods. The 2D site representation reveals the electron-hole coherence on excitation. The 3D transition density shows the orientation and strength of the transition dipole moment, and the 3D charge difference density gives the orientation and result of the intramolecular charge transfer. Also, photoinduced intermolecular charge transfer (ICT) in PBTDP-TPA-fullerene triad are identified with 2D and 3D representations, which reveals the mechanisms of ICT in donor-bridge-acceptor triad on excitation. Besides that we also found that the direct superexchange ICT from donor to acceptor (tunneling through the bridge) strongly promotes the ICT in the donor-bridge-acceptor triad.     

Stability of atomic oxygen chemisorption on Pt‐alloy surfaces

A density functional theory calculation is used to investigate the atomic oxygen (O) stability over platinum (Pt) and Pt‐based alloy surfaces. Here, the stability is connected with the preferential adsorption sites for O chemisorptions and the adsorption energy. Thus, the interaction mechanism between atomic O and metal surfaces is studied by using charge transfer analysis. In this present paper, atomic structure and binding energy of oxygen adsorption on the Pt(111) are in a very good agreement with experiment and previous density functional theory calculations. Furthermore, we obtained that the addition of ruthenium (Ru) and molybdenum (Mo) on the pure Pt surface enhances the adsorption energy. Our charge transfer analysis shows that the largest charge transfer contributing to the metal‐O bonding formation is observed in the case of O/PtRuMo surface followed by O/PtRu surface. This is in consistency with metal d‐orbital characteristic, where Mo has much more empty d‐orbital than Ru in correspondence to accept electrons from atomic oxygen. Copyright © 2016 John Wiley & Sons, Ltd.     

Time-dependent density functional theory study of charge transfer in collisions

We study the charge transfer between colliding ions, atoms, or molecules, within time-dependent density functional theory. Two particular cases are presented, the collision between a proton and a Helium atom, and between a gold atom and a butane molecule. In the first case, proton kinetic energies between 16?keV and 1.2?MeV are considered, with impact parameters between 0.31 and 1.9 ?. The partial transfer of charge is monitored with time. The total cross-section is obtained as a function of the proton kinetic energy. In the second case, we analyze one trajectory and discuss spin-dependent charge transfer between the different fragments.     

Theoretical study of the charge carrier mobilities of the molecular materials tetrathiafulvalene (TTF) and 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP)

Tetrathiafulvalene (TTF) is a kind of fused ring aromatic compound containing four sulfur atoms in one molecule, which is well known as a charge transport material. In order to calculate the charge mobility of this semiconductor, Marcus electron transfer theory and the embedded model, which can give small intramolecular reorganization energies, were employed. The calculated results were in good agreement with the experimental values, so the above computing model is appropriate to assess the electrical property of TTF. On this basis, we predicted the charge mobility of 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) crystals, for which the molecular structure is similar to TTF. The calculated results indicated that BDH-TTP is a p-type material, which has a better performance than TTF in hole transfer due to larger hole coupling and the smaller hole injection barrier. In addition, the direct coupling (DC) and the site energy correction (SEC) methods were used to calculate the charge transfer integrals. Although the results were slightly different, the qualitative trends were the same. Furthermore we took into account the anisotropic transfer properties of TTF and BDH-TTF, since obviously the mobilities along one dimension are larger than those along three dimensions. Finally, natural bond orbital analysis was used to study the interactions in all of the dimers.     

Theory and application of cyclic voltammetry at a hemispherical microelectrode for a quasi-reversible reaction

The theory of cyclic voltammetry for a quasi-reversible reaction at a hemispherical microelectrode has been deduced. From the results calculated according to the theory, the heterogeneous rate constant and charge transfer coefficient can be measured with the cyclic voltammetric data obtained at an intermediate scan rate on a hemispherical microelectrode. To verify the theory, the kinetic constant for reduction of benzoquinone in acetonitrile has been determined. The result is coincident with that measured by a fast scan rate at a platinum microdisk electrode. The kinetic constant and charge transfer coefficient for reduction of 2,3,5,6-tetrachlorobenzoquinone have also been determined with the method described in this paper.     

Finite-thickness-enhanced attractions for oppositely charged membranes and colloidal platelets

Within linearized Poisson-Boltzmann theory, we study the disjoining pressure of two oppositely charged parallel objects (membranes and colloidal platelets) in a 1:1 electrolyte, with a focus on the effects of their finite thickness. This extension of the standard Gouy-Chapman model from an interacting pair of double layers to a quartet (one on each side of the two interacting objects) is shown to enhance the regime of attractive interactions significantly, in particular, when the separation and the thickness are on the order of the Debye length of the solvent, provided the dielectric mismatch between objects and solvent is not too extreme. The enhancement of attractions occurs for objects with fixed charge as well as for those that exhibit charge regulation but not for those with a constant surface potential. The underlying mechanism for this enhancement for thin objects is the transfer of net ionic charge from the electrolyte in between to the other sides. For biological membranes in water, this effect is small; however, it is due to strong image charge effects.     

Charge transfer at biotic/abiotic interfaces in biological electrocatalysis

In this opinion paper, we discuss the charge transfer at biotic/abiotic interfaces in man-made and biological electrochemical systems. Specifically, we will first introduce the heterogeneous charge transfer at the bioelectrode interface, followed by the intramolecular change transfer in peptide and protein structures, and finally discuss the extracellular charge transfer in electrogenic microorganisms. In addition to discussion of charge transfer mechanisms and synthetic structures/scaffolds required for it, a particular focus will be given to novel experimental designs that are able to bring new concepts and boost mechanism understanding and applications development. There are also discussions on the combination of modern computational techniques and experimental characterizations.