Study of the Electrical Double Layer of a Spherical Micelle: Functional Theoretical Approach

The electrical double layer theory is the base of the colloid stability theory (DLVO theory), and the PB eq. is a key to the study of the layer1,2. For a spherical particle, the PB eq. is (1) where and are the dielectric constant of the medium, the valence of ions, the elementary charge, the concentration of ions far away from the particle, the Boltzmann's constant and the temperature of the system, respectively. Since this eq. is a second order nonlinear differential one, only the anal…     

Quantum Chemical Study of Potential Energy Surface in the Formation of Atmospheric Sulfuric Acid?

A new potential energy surface (PES) for the atmospheric formation of sulfuric acid from OH+SO₂ is investigated using density functional theory and high-level ab initio molecular orbital theory. A pathway focused on the new PES assumes the reaction to take place between the radical complex SO₃·HO₂ and H₂O. The unusual stability of SO₃·HO₂ is the principal basis of the new pathway, which has the same final outcome as the current reaction mechanism in the literature but it avoids the production and complete release of SO₃. The entire reaction pathway is composed of three consecutive elementary steps:(1) HOSO₂+O₂→SO₃·HO₂, (2) SO₃·HO₂+H₂O→SO₃·H₂O·HO₂, (3) SO₃·H₂O·HO₂→H₂SO₄+HO₂. All three steps have small energy barriers, under 10 kcal/mol, and are exothermic, and the new pathway is therefore favorable both kinetically and thermodynamically. As a key step of the reactions, step (3), HO₂ serves as a bridge molecule for low-barrier hydrogen transfer in the hydrolysis of SO₃. Two significant atmospheric implications are expected from the present study. First, SO₃ is not released from the oxidation of SO₂ by OH radical in the atmosphere. Second, the conversion of SO₂ into sulfuric acid is weakly dependent on the humidity of air.     

Theoretical Study on the Mechanism of the Gas-phase Reaction of Sc＋ with Propargyl Alcohol

In order to elucidate the reaction mechanisms of reaction Sc^＋ with propargyl alcohol (PPA), the triplet potential energy surface for the reactions has been theoretically investigated using a DFT method. The geometries for the reactants, intermediates, transition states and products were completely optimized at B3LYP/DZVP level. The single point energy of each stationary point was calculated at MP4/(6-311＋G** for C, H, O and Lanl2dz for Sc^＋) level. All the transition states were verified by the vibrational analysis and the internal reaction coordinate (IRC) calculations. The present results show that the reaction takes an insertion-elimination mechanism both along the O—H and C—O bond activation branches, but the C—O bond activation is much more favorable in energy than the O—H bond activation. All theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction.     

Study on Electric Double Layer of a Cylindrical Particle with Functional Theoretical Approach

A new method, i.e. the iterative method in functional theory, was introduced to solve analytically the nonlinear Poisson-Boltzmann （PB） equation under general potential ψ condition for the electric double layer of a charged cylindrical colloid particle in a symmetrical electrolyte solution. The iterative solutions of ψ are expressed as functions of the distance from the axis of the particle with solution parameters： the concentration of ions c, the aggregation number of ions in a unit length m, the dielectric constant e, the system temperature T and so on. The relative errors show that generally only the first and the second iterative solutions can give accuracy higher than 97%. From the second iterative solution the radius and the surface potential of a cylinder have been defined and the corresponding values have been estimated with the solution parameters, Furthermore, the charge density, the activity coefficient of ions and the osmotic coefficient of solvent were also discussed,     

Optimal Initialization of a Quantum System for an Efficient Coherent Energy Transfer?

For an energy transfer network, the irreversible depletion of excited electron energy occurs through either an efficient flow into an outer energy sink or an inefficient decay. With a small decay rate, the energy transfer efficiency is quantitatively reflected by the average life time of excitation energy before being trapped in the sink where the decay process is omitted. In the weak dissipation regime, the trapping time is analyzed within the exciton population subspace based on the secular Redfield equation. The requirement of the noise-enhanced energy transfer is obtained, where the trapping time follows an exact or approximate 1/Γ-scaling of the dissipation strength Γ. On the opposite side, optimal initial system states are conceptually constructed to suppress the 1/Γ-scaling of the trapping time and maximize the coherent transfer efficiency. Our theory is numerically testified in four models, including a biased two-site system, a symmetric three-site branching system, a homogeneous onedimensional chain, and an 8-chromophore FMO protein complex.     

Theoretical Study of Adsorption and Dehydrogenation of C2H4 on Cu(410)?

Adsorption and dehydrogenation of ethylene on Cu(410) surface are investigated with firstprinciples calculations and micro-kinetics analysis. Ethylene dehydrogenation is found to start from the most stable π-bonded state instead of the previously proposed di-σ-bonded state. Our vibrational frequencies calculations verify the π-bonded adsorption at step sites at low coverage and low surface temperature and di-σ-bonded ethylene on C-C dimer (C₂H₄-CC) is proposed to be the species contributing to the vibrational peaks experimentally observed at high coverage at 193 K. The presence of C₂H₄-CC indicates that the dehydrogenation of ethylene on Cu(410) can proceed at temperature as low as 193 K.     

How Machine Learning Accelerates the Development of Quantum Dots?†

With the rapid developments in the field of information technology, the material research society is looking for an alternate scientific route to the traditional methods of trial and error in material research and process development. Machine learning emerges as a new research paradigm to accelerate the application‐oriented material discovery. Quantum dots are expanded as functional nanomaterials to enhance cutting‐edge photonic technology. However, they suffer from uncertainty in industrial fabrication and application. Here, we discuss how machine learning accelerates the development of quantum dots. The basic principles and operation procedures of machine learning are described with a few representative examples of quantum dots. We emphasize how machine learning contributes to the optimization of synthesis and the analysis of material characterizations. To conclude, we give a short perspective discussing the problems of combining machine learning and quantum dots.     

Theoretical Study on the Mechanism Properties of a Novel Trans-platinum Antitumor Drug

1 INTRODUCTION Cis-diamminedichloroplatinum(II) (cis-DDP) is a widely used drug in dealing with many human carcinomas, such as testicular carcinoma, ovarian carcinoma, etc.[1～4]. Despite of its great success in treating many kinds of cancers, the antitumor drug does have many limitations, for example, several side effects or both intrinsic and acquired resis- tance[5, 6]. In order to solve these problems, various platinum complexes have been tested over the past years[7～19]. The clas…     

Dynamic Variation of Excitonic Coupling in Excited Bilayer Graphene Quantum Dots?

The intermolecular interaction determines the photophysical properties of the organic aggregates, which are critical to the performance of organic photovoltaics. Here, excitonic coupling, an important intermolecular interaction in organic aggregates, between the π-stacking graphene quantum dots is studied by using transient absorption spectroscopy. We find that the spectral evolution of the ground state bleach arises from the dynamic variation of the excitonic coupling in the excited π-stacks. According to the spectral simulations, we demonstrate that the kinetics of the vibronic peak can be exploited as a probe to measure the dynamics of excitonic coupling in the excited π-stacks.     

Accurate Calculation of Equilibrium Reduced Density Matrix for the System-Bath Model: a Multilayer Multiconfiguration Time-Dependent Hartree Approach and its Comparison to a Multi-Electronic-State Path Integral Molecular Dynamics Approach?

An efficient and accurate method for computing the equilibrium reduced density matrix is presented for treating open quantum systems characterized by the system-bath model. The method employs the multilayer multiconfiguration time-dependent Hartree theory for imaginary time propagation and an importance sampling procedure for calculating the quantum mechanical trace. The method is applied to the spin-boson Hamiltonian, which leads to accurate results in agreement with those produced by the multi-electronic-state path integral molecular dynamics method.     

A Hierarchical-Equation-of-Motion Based Semiclassical Approach to Quantum Dissipation?

We present a semiclassical (SC) approach for quantum dissipative dynamics, constructed on basis of the hierarchical-equation-of-motion (HEOM) formalism. The dynamical components considered in the developed SC-HEOM are wavepackets' phase-space moments of not only the primary reduced system density operator but also the auxiliary density operators (ADOs) of HEOM. It is a highly numerically efficient method, meanwhile taking into account the high-order effects of system-bath couplings. The SC-HEOM methodology is exemplified in this work on the hierarchical quantum master equation[J. Chem. Phys. 131 , 214111 (2009)] and numerically demonstrated on linear spectra of anharmonic oscillators.     

Influence of Molecular Structure on the Dimerization Reactivity of Germaaromatic Compounds： a Theoretical Study

Density functional theory (DFT) calculations, at the B3LYP/6-311G** level of theory, were performed to study the reaction mechanism and potential energy surface of the [2 + 2], [4 + 2] and [4 + 4] dimerization reactions of some germaaromatic compounds. The influence of reactant's molecular structure and benzene solvent on the potential energy surface of the studied reactions was investigated. Our calculation results show that [2 + 2] and [4 + 4] reactions are concerted and synchronous processes; while [4 + 2] reactions proceed via a concerted but asynchronous way in general. [2 + 2] and [4 + 2] reactions of germabenzenes and 1-germana- phthalene proceed much more easily than the corresponding [4 + 4] reaction, both thermo- dynamically and kinetically; while most [4 + 2] paths have lower activation barrier than the corres- ponding [2 + 2] ones. As the number of six-membered aromatic rings in reactant molecules becomes larger, [2 + 2], [4 + 2] and [4 + 4] reactions become easier to proceed. The influence of substituents at the Ge atom of germabenzenes on the potential energy surface of [2 + 2] and [4 + 2] reactions correlates with their electronic properties and volume. Solvent effect is not crucial for the potential energy surfaces of the studied reactions.     

Theoretical study of the energies and activation barriers of elementary reactions of hydrogenation of the Ti-doped closo-aluminide cluster Al@TiAl11 and its anion Al@TiAl 11?

The potential energy surfaces, energies E, and activation barriers h of elementary reactions of addition of an H₂ molecule to the Ti-doped closo-aluminide cluster Al@TiAl₁₁ and its anion Al@Ti₁₁⁻ with an icosahedral and marquee structure in the states with different multiplicity were calculated within the B3LYP approximation of the density functional theory using the 6–31G* and 6–311+G* basis sets. The results were compared with the data calculated at the same level of theory for the related reactions of hydrogenation of bare closo-aluminides Al₁₃ and Al₁₃⁻ and their B-, C-, Si-, and Ge-doped derivatives. The computations demonstrated that, depending on the structure, charge, and multiplicity of the Al@TiAl₁₁ cluster, the hydrogenation energy varies in the range 15–23 kcal/mol. At the first stage of addition (chemisorption) of H₂, a μ-H₂ complex at the Ti atom (intermediate) forms with the distance R(Ti-H₂) ∼ 1.9–2.0 ?, which is accompanied by an energy decrease of ∼4–10 kcal/mol. The H-H bond in the μ-H₂ complex is ∼0.1 ? longer and the stretching vibration frequency V_val(HH) is ∼700–1500 cm⁻¹ (or more) lower than the corresponding characteristics of the isolated H₂ molecule. In the transition state with an imaginary frequency of ∼600i–1100i, the H₂ molecule is coordinated to the attacked edge Ti-Al_r, and its length increases to ∼0.9–1.1 ?. The activation barrier height h varies from a few kcal/mol to ∼8–10 kcal/mol when measured from the μ-H₂ complex and is within 18–22 kcal/mol when measured from the product (dihydride Al@TiAl₁₁H₂). The latter barrier (to the reverse reaction of dehydrogenation) is considerably higher than the barriers to migration of hydrogen atoms around the metal cage in the Al@TiAl₁₁H₂ dehydrides. There is a correlation between the energies E and barriers h of hydrogenation reactions and the structure, external charge, and multiplicity of the Al@TiAl₁₁ cluster. In all cases, the hydrogenation should occur significantly more readily than dehydrogenation. It was shown that these reactions can be both irreversible (for example, for an icosahedron in the singlet state) and reversible (for a marquee in the triplet state and others). The conclusion was drawn that the elementary reactions of hydrogenation and dehydrogenation for Ti-doped aluminides should occur considerably faster and under milder conditions than for bare aluminides or their analogues doped with main-group atoms. Original Russian Text ? V.K. Charkin, O.P. Kochnev, N.M. Klimenko, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 8, pp. 1345–1354.     

Average Arrival Time: an Alternative Approach for Studying Fluorescent Behavior of Single Quantum Dots?

Due to photoluminescence intermittency of single colloidal quantum dots (QDs), the traditional exponential fluorescence lifetime analysis is not perfect to characterize QDs' fluorescent emission behavior. In this work we used the time-tagged time-resolved (TTTR) mode to record the fluorescent photons from single QDs. We showed that this method is compatible with the traditional lifetime analysis. In addition, by constructing the trajectory over time and the distribution of average arrival time (AAT) of the fluorescent photons, more details about the emission behavior of QDs were revealed.     

Kinetic study of the oxidation of L-threonine by MnO4? ions

A self-catalytic effect attributed to Mn²⁺ ions was observed when studying the oxidation of L-threonine by permanganate ions. The process obeys the rate equation:

Influence of anion sizes on the formation of substitutional solid solutions in clathrate hydrate frameworks in the series of tetrabutylammonium hydroxide-tetrabutylammonium halide (F?, Cl?, Br?, or I?)-water systems

In the tetrabutylammonium iodide-tetrabutylammonium hydroxide-water system, solubility isotherms at 10 and 17°C were studied and two solid solutions based on tetrabutylammonium hydroxide clathrate hydrate were found to form, one tetragonal solution with 1: 32 composition (salt: water) and the other cubic with the 1: 28 composition. The influence of halide anions on the formation of substitutional solid solutions in the series of tetrabutylammonium hydroxide-tetrabutylammonium halide (F⁻, Cl⁻, Br⁻, and I⁻)-water systems was considered. Original Russian Text ? L.S. Aladko, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 7, pp. 1224–1228.     

Constrained Density Functional Theory Plus the Hubbard U Correction Approach for the Electronic Polaron Mobility: A Case Study of TiO2?

The formation and migration of polarons have important influences on physical and chemical properties of transition metal oxides. Density functional theory plus the Hubbard \begin{document}$U$\end{document} correction (DFT+\begin{document}$U$\end{document}) and constrained density functional theory (cDFT) are often used to obtain the transfer properties for small polarons. In this work we have implemented the cDFT plus the Hubbard \begin{document}$U$\end{document} correction method in the projector augmented wave (PAW) framework, and applied it to study polaron transfer in the bulk phases of TiO\begin{document}$_2$\end{document}. We have confirmed that the parameter \begin{document}$U$\end{document} can have significant impact on theoretical prediction of polaronic properties. It was found that using the Hubbard \begin{document}$U$\end{document} calculated by the cDFT method with the same orbital projection as used in DFT+\begin{document}$U$\end{document}, one can obtain theoretical prediction of polaronic properties of rutile and anatase phases of TiO\begin{document}$_2$\end{document} in good agreement with experiment. This work indicates that the cDFT+\begin{document}$U$\end{document} method with consistently evaluated \begin{document}$U$\end{document} is a promising first-principles approach to polaronic properties of transition metal oxides without empirical input.     

Theoretical studies on N-loss predissociation mechanisms of N2O+ (A?2Σ+) in Cs symmetry

The N-loss predissociation mechanisms of the A ²Σ⁺ (2 ² A′) state of N₂O⁺ to the first and second dissociation limits were studied in the C _s symmetry. The potential energy curves (PECs) and minimum energy crossing points (MECPs) for the C _s states of N₂O⁺ were calculated at the CAS levels. On the basis of our CAS calculation results (CASPT2 energetic results and CASSCF spin orbit couplings), we suggest two processes for N-loss predissociation mechanisms of A ²Σ⁺ (2 ² A′) to the first and second limits. The first two steps in the two processes are the same: A ²Σ⁺ passes through the 2 ² A′/1 ⁴ A″ MECP and then reaches the 1 ⁴ A″ (1 ⁴Σ⁻) PEC. The 2 ² A′/1 ⁴ A″ MECP has a bent geometry and is slightly higher in energy than the transition state along the 1 ⁴ A″ PEC. Our mechanisms are different from the previously suggested mechanisms (via 1 ⁴Π).     

Kinetic model for the Bray-Liebhafsky process without the reaction IO3?+I?+2H+?HIO+HIO2

Oscillations in the concentration of intermediates were obtained when a model without reaction IO ₃ ^– +I^–+2H⁺HIO+HIO₂ was used for the simulation of the Bray-Liebhafsky process.