A method for molecular correlation energy calculations. Application to the determination of dissociation energies of diatomic and polyatomic molecules

A simple and economical method for molecular correlation energy calculations is developed. In this method, the internal part of the correlation energy is calculated by means of a CI in a minimal basis set and the non-internal part (semi-internal and all-external) is evaluated using an original atoms-in-molecule method. It is successfully applied to the determination of dissociation energies of some diatomic (H₂, NH, C₂, CN, N₂, CO, NO, O₂, F₂) and polyatomic (H₂O, N₂O, CO₂, N₃H, CH₂N₂, CH₂CO, C₂N₂) molecules. The results are compared to those obtained using very elaborate variational methods.Aspirant du Fonds National Belge de la Recherche Scientifique.     

Partitioning of atomization energy

The present work provides a technique for partitioning the atomization energy of a molecule into diatomic contributions. The method is largely based on the redistribution of the kinetic energy term in Mayer's energy partitioning and uses free‐atom energies as a reference. The comparison of Mayer's original method, the alternative Ichikawa–Yoshida approach, and the new atomization energy partitioning (AEP) shows that the new approach has advantages in describing trends in diatomic energies in molecules with triple bonds, as well as for hydrogen bonds. The proposed AEP is a viable alternative to Mayer's energy partitioning method. © 2007 Wiley Periodicals, Inc. Int. J. Quantum Chem, 2008     

Interaction energy contours of molecules as probed by a test atom

Potential energy contour curves for some simple molecules interacting with a test atom (a Li atom in the ground state) are calculated by theab initio method. Relative hardness of the repulsive molecular surface is found to be anisotropic. This indicates that the outer boundary surface of a molecule changes its form depending on the extent of applied external forces. The attractive nature of the molecular surface is demonstrated to be local. Surroundings of electronegative atoms having nonbonded electron pairs are found to be attractieve to the test atom having both electron-donating and electron-accepting abilities.     

A representation of the polarization term in the interaction energy between a molecule and a point-like charge

The interaction energy of a molecule M with a point-like charge q can be partitioned into simpler contributions, two of which can be expressed in terms of the charge distribution _M of the sole M. The first term, qV(r), represents the interaction of q with the undistorted charge _M ⁰ of M while the second q ² P(r) gives the additional contributions due to the polarization of _M ⁰ under the influence of the charge q placed at the point r. In this paper we investigate the possibility of getting an inexpensive and sufficiently accurate analytical representation of P(r) over the whole space outside the van der Waals volume of M.     

Synthesis of Imines via Reactions of Benzyl Alcohol with Amines Using Half‐Sandwich (η6‐p‐cymene) Ruthenium(II) Complexes Stabilised by 2‐aminofluorene Derivatives

A new class of half‐sandwich (η⁶‐p‐cymene) ruthenium(II) complexes supported by 2‐aminofluorene derivatives [Ru(η⁶‐p‐cymene)(Cl)(L)] ( L  = 2‐(((9H‐fluoren‐2‐yl)imino)methyl)phenol ( L ¹ ), 2‐(((9H‐fluoren‐2‐yl)imino)methyl)‐3‐methoxyphenol ( L ² ), 1‐(((9H‐fluoren‐2‐yl)imino)methyl)naphthalene‐2‐ol ( L ³ ) and N‐((1H‐pyrrol‐2‐yl)methylene)‐9H‐fluorene‐2‐amine ( L ⁴ )) were synthesized. All compounds were fully characterized by analytical and spectroscopic techniques (IR, UV–Vis, NMR) and also by mass spectrometry. The solid state molecular structures of the complexes [Ru(η⁶‐p‐cymene)(Cl)(L²)], [Ru(η⁶‐p‐cymene)(Cl)(L³)] and [Ru(η⁶‐p‐cymene)(Cl)(L⁴)] revealed that the 2‐aminofluorene and p‐cymene moieties coordinate to ruthenium(II) in a three‐legged piano‐stool geometry. The synthesized complexes were used as catalysts for the dehydrogenative coupling of benzyl alcohol with a range of amines (aliphatic, aromatic and heterocyclic). The reactions were carried out under thermal heating, ultrasound and microwave assistance, using solvent or solvent free conditions, and the catalytic performance was optimized regarding the solvent, the type of base, the catalyst loading and the temperature. Moderately high to very high isolated yields were obtained using [Ru(η⁶‐p‐cymene)(Cl)(L⁴)] at 1 mol%. In general, microwave irradiation produced better yields than the other two techniques irrespective of the nature of the substituents.     

能源转换演示装置的设计

针对高中化学教材中提到的新能源问题,探索设计了可将太阳能转化为电能,电能转化为化学能,化学能转化为电能,电能转化为热能的能源转换演示装置。通过该实验的演示,可以让学生直观地感受到几种能量之间的转化过程,可供教学参考和借鉴。     

Influence of multivalent ions on power production from mixing salt and fresh water with a reverse electrodialysis system

Reverse electrodialysis is a membrane-based technique for production of sustainable electricity from controlled mixing of a diluted electrolyte solution (e.g., river water) and a concentrated electrolyte solution (e.g., sea water). Reverse electrodialysis has been investigated with pure sodium chloride solutions. In practice, however, in most cases also other ions are present in both feed solutions. In the present paper, the effect of multivalent ions on the performance of a reverse electrodialysis stack was investigated. Results show that, besides a higher stack resistance in presence of multivalent ions, especially the presence of multivalent ions in the dilute solution has a lowering effect on the stack voltage. This can be explained by an observed transport of these ions from the diluted electrolyte solution to the concentrated electrolyte solution. In order to prevent or hamper this transport against the activity gradient, monovalent-selective membranes can be used. This shows indeed better results with respect to the stack voltage. Therefore, it would be beneficial to use monovalent-selective membranes in reverse electrodialysis, especially in the case of a relatively high content of multivalent ions in the dilute (i.e., in the first stages of the installation where the sodium chloride content in the dilute is still relatively low).     

Electron impact ionization of amines using crossed electron-molecular beams

Ionization energy functions of triethyl amine, tri-n-propyl amine, N,N-dimethyl-benzenamine and N,N-diethyl-benzenamine, and appearance energy functions of major products of dissociative ionization have been measured using a high sensitivity crossed electron beam-molecular beam apparatus incorporating a quadrupole mass spectrometer and an on-line laboratory computer. The data obtained is useful in understanding the role of dopants in gas laser plasmas.     

Efficient calculation of two-dimensional adiabatic and free energy maps: Application to the isomerization of the C13C14 and C15N16 bonds in the retinal of bacteriorhodopsin

Accurate calculation of potential energy and free-energy profiles along reaction coordinates of biological processes such as enzymatic reactions or conformational changes is fundamental to the obtention of theoretical insight into protein function. We describe here the practical implementation of the Automatic Map Refinement Procedure (AMRP) and two-dimensional Weighted Histogram Analysis Method (WHAM) for efficient computation of adiabatic potential energy and free-energy maps, respectively. Methods for efficiently sampling configuration space with high-energy barriers and for removing hysteresis in the case of periodic reaction coordinates are presented. The application of these techniques to the isomerization of the C13C14 and C15N16 bonds in the retinal of bacteriorhodopsin is described. In dark-adapted bacteriorhodopsin (bR), the retinal moiety exists in two conformers, all-trans and (13,15)cis, with the latter making ≃67% of the population. This experimental free energy difference is reproduced here to within k_BT. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1644–1658, 1999     

太阳能光解水制氢的研究进展

本文概述了利用光催化技术催化分解水制氢的反应机理和研究进展。结合作者的最近研究,重点描述了TiO2及过渡金属氧化物,层状金属氧化物以及某些能利用可见光的光催化材料的结构和光催化特性,阐述了核课题的意义和今后的研究方向。     

First principle calculations study of AlN surface terminal structure evolution under different conditions

The surface structure and properties of aluminum nitride (AlN) play an important role in many applications. Using the first principle calculations method, we analyzed the surface terminal structure of AlN and its evolution under different conditions by determining the surface energy, adsorption energy, and evaporation energy of the Al and N terminals on the AlN(0001) surface. Our results show that the reason why the N terminal is less stable than the Al terminal is not only because of its high surface energy but also because its adsorption performance is extremely sensitive to the adsorption position. The surface N atoms combine to form N₂ molecules that escape during the evaporation process at high temperature. After surface N atoms escape, the AlN surface structure reconstitutes to form a hexagonal closest packing (HCP)–like structure, and the energy barrier for the reconstructing process is 3.2 eV. This shows that the structure and form of the AlN(0001) terminals depend on the environmental conditions.     

基于共振能量转移的生物传感器在食品安全检测中的应用研究进展

共振能量转移(Resonance energy transfer,RET)是一种发生在供体和受体之间的非辐射能量转移过程。RET的能量转移效率对供体和受体间的距离变化非常敏感,可被用于开发新型的光学生物传感器。与传统光学生物传感器相比,基于RET的生物传感器无需洗涤及分离过量标记物等步骤,可大幅简化检测流程。因RET具有灵敏度高、操作简便及速度快等优点,近年来,在医学诊断、生命科学研究、环境监控以及食品安全检测等领域备受关注。该文根据能量供体的不同,将RET分为3种类型：荧光共振能量转移(Fluorescence resonance energy transfer,FRET)、生物发光共振能量转移(Bioluminescence resonance energy transfer,BRET)和化学发光共振能量转移(Chemiluminescence resonance energy transfer,CRET)。并分别对基于上述3种RET类型的生物传感器在食品安全检测中的应用研究进展进行了综述,同时对其应用前景和发展趋势进行了展望。     

面向能源领域的石墨烯研究

化石能源枯竭以及地球环境污染已经成为并且在未来相当长一段时期内都将是人类面临的最严峻的危机之一.因此,寻找清洁的替代能源形式、有效的能量存储方式以及高效的能源利用途径是目前科学研究的热点.自从其高质量样品被制备和研究以来,石墨烯一直吸引着全世界科研工作者的兴趣;它的一系列独特的物理化学性质,为其在能源领域的应用提供了无限前景.本文对石墨烯在能源领域的最新研究进展以及其工业化应用作了简要综述,具体内容包括石墨烯材料在以下领域的应用：能源储存器件类,如超级电容器和锂离子电池;能源转化装置类,如燃料电池和太阳能电池.     

Theoretical study on the potential energy surface and vibrational energy levels of HXeI

The potential energy surface for the electronic ground state of the HXeI molecule is constructed by using the internally contracted multi-reference configuration interaction with the Davidson correction（icMRCI＋Q）method and large basis sets. The stabilities and dissociation barriers are identified from the potential energy surfaces.The three-body dissociation channel is found to be the dominate dissociation channel for HXeI.Based on the obtained potentials,vibrational energy levels of HXeI are calculated using the Lanczos algorithm.Our theoretical results are in excellent agreement with the available observed values.     

An Application of the Dynamical Lie Algebraic Method to Potential Energy Surface of the Stable Linear Asymmetric Tetratomic Molecules

Potential energy surfaces play an important role in studying theoretical chemistry. In the present paper, we first use the dynamical symmetry group G = U ₁(4) U ₂(4) U ₃(4) to get the expression of the potential energy surface for the stable linear asymmetric tetratomic molecules with the stretching vibration and the dissociation energy. The method can be applied to a number of stable tetratomic molecules. As an example we use the method to calculate the potential energy surface of C₂HD.     

Characterization of cyclodextrin glycosyltransferase from Bacillus firmus strain No. 37

The enzyme cyclod extringly cosyltransferase (CGTase), EC2.4.1.19, which produces cyclodextrins (CDs) from starch, was obtained from Bacillus firmus strain no. 37 isolated from Brazilian soil and characterized in the soluble form using as substrate 100 g/L of maltodextrin in 0.05 M Tris-HCl buffer, 5 mM CaCl₂, and appropriate buffers. Enzymatic activity and its activation energy were determined as a function of temperature and pH. The activation energy for the production of β- and γ-CD was 7.5 and 9.9 kcal/mol, respectively. The energy of deactivation was 39 kcal/mol. The enzyme showed little thermal deactivation in the temperature range of 35–60°C, and Arrhenius-type equations were obtained for calculating the activity, deactivation, and half-life as a function of temperature. The molecular weight of the enzyme was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, giving 77.6k Da. Results for CGTase activity as a function of temperature gave maximal activity for the production of β-CD at 65°C, pH 6.0, and 7 1.5 mmol of β-CD/(min·mg of protein), whereas for γ-CD it was 9.1 m mol of γ-CD/(min·mg of protein) at 70°C and pH 8.0. For long contact times, the bestuse of the enzymatic activity occurs at 60°C oratalower temperature, and the reaction pH may be selected to increase the vield of a desired CD.     

Solar energy and solid state chemistry

The transition from reliance on fossil fuels to long-term energy sources is a most urgent technical challenge to modern civilization. This paper outlines some materials problems associated with the transition to solar energy as a distributed source of (a) low-temperature heat for hot water, domestic heating, and refrigeration/air-conditioning, (b) electric power, and (c) fuel. Academy lecture delivered at the Indian Institute of Science, Bangalore, on 6 December 1978.     

Simple molecular wavefunctions with correlation corrections II

The potential curves for the ground state of Li₂ (¹ _g ⁺ ) and FH (¹ _g ⁺ ) are computed. The correlation energy is calculated using a functional of the one- and two-electron density matrices derived from an MC SCF reference wavefunction and is added to the reference energy to obtain a correlated potential curve.     

Theoretical Studies on the Potential Energy Surface and Vibrational Energy Levels of HXeBr

The potential energy surface for the electronic ground state of the HXeBr molecule is constructed from more than 4200 ab initio points calculated using the internally contracted multi-reference configuration interaction method with the Davidson correction （icMRCI ＋ Q）. The stabilities and dissociation barriers are identified from the potential energy surface. The three-body dissociation channel is found to be the dominant dissociation channel for HXeBr. Low-lying vibrational energy levels of HXeBr calculated using the Lanczos algorithm are found to be in good agreement with the available experimental band origins.     

Electronic energy inequalities for isoelectronic molecular systems

Within the Born-Oppenheimer approximation an inequality relation is derived between points of electronic energy hypersurfaces of pairs of isoelectronic molecules. The inequality is directly applicable to point pairs fulfilling a symmetry criterion for the nuclear frameworks and it may be extended to coordinate domains on both hypersurfaces. The result is applied to special examples of conformational problems, dissociation reactions and impurity —vacancy centres in solid clusters.