Heavy Atom Effect on the First Hyperpolarizabilities of Squaric Acid Homologues Studied by Ab Initio and DFT Methods

1 INTRODUCTION In the past decades, there have been great efforts to research on the molecules nonlinear opti- cal (NLO) properties in which theoretical calcu- lation[1～3] became a powerful tool because it not only explains the micro-mechanism of the mo…     

3，4－二硫方酸的从头算研究

在６－３１Ｇ水平上对３，４－二硫方酸（３，４－二巯基－３－环丁烯－１，２－二酮）的３种平面构象异构体进行ＳＣＦ计算．结果表明，ＺＺ型异构体最稳定，ＺＥ型次之，从等键反应能量分析３，４－二硫方酸的稳定性，与苯作比较探讨其芳香性．并在６－３１Ｇ水平上计算了３种构象的振动频率．     

氮的三原子化合物的从头算及密度泛函研究

在6-311+G*基组水平上,对氮的三原子化合物N3-、N3、N3+,用MP2及六种密度泛涵方法进行了研究.结果表明,对于已知结构的化合物的计算结果与实验测定值非常吻合,对实验上未知的化合物分子的稳定几何构型及其有关参数进行了新的探讨和补充,同时比较了N3-、N3、N3+间相对稳定性和几何性质,并讨论了几种不同方法对该化合物系列诸性质参数的影响,结合MO理论及成键能的计算结果进行了成键分析.     

Ab Initio Study of the Excited State Decomposition Reactions of Monothioformic Acid

IntroductionTherehasbeenconsiderableinterestinrecentyearsinthetheoreticalstudyofthemonothioformicacid1ed.However,mostofthemhaveconcentIatedontheelectronicproperties,isomerizationandintramolecularhydrogenshiftreactionsoftheacid,andstudiesonitschemicalreactionshaverarelybeenrepofted.Recently,wereportedonthetheoreticalstudyofthegroundstateunimolecularpyrolysisofmonothioforndcacid,andtheresultsshowedthathightemperatureisneededforitsgroundstatedecompositionreactions.Asapotentialinterstellarcompoun…     

丙酮酸分子结构与振动光谱的密度泛函理论研究

用密度泛函方法BLYP、B3LYP和从头算Hartree-Fock(HF)方法在6-31G*基组水平上对丙酮酸分子的几何结构（甲基的重叠式和交错式两种构象）和振动光谱分别进行了优化和计算,并给出了各种频率所对应的红外强度及拉曼活性,对光谱进行了指认。结果表明：在丙酮酸分子的两种构象中,重叠式比较稳定*B3LYP计算得到的构型参数与实验结果比较一致;在振动频率的计算中,BLYP未标度力场所计算的非CH3伸缩振动基频预测值和实验值的平均绝对偏差为10.4cm-1;而HF标度力场的平均绝对偏差为17.9cm-1。说明两者的结果与实验观测频率比较吻合,但B3LYP的频率计算值偏差（38.3cm-1）较大。根据振动频率的势能分布和红外光谱强度对此分子的振动基频进行了理论归属。     

Ab Initio Study on the Isomerization and Dehydrogenation of Methylnitrene

The ab initio calculations were performed at the RHF/4-31G level with the reaction pathways of the iso-merization and dehydrogenation of methylnitrene by the intrinsic reaction coordinate method. The results show that the transformation from methylnitrene to methylenimine would be very easy. This accountes for the experimental fact that one couldn' t find the methylnitrene, but only obtained the methylenimine in the pyrolysis of methyl azide. The mode-selective study reveals the reaction coordinates (IRC) of isomerization and dehydrogenation of methylnitrene are associated with the molecular deformation mode of 1191 cm-1 and the methyl group unsymmetrical stretch mode, respectively. The coupling between normal coordinates is favourable to select the reaction channel of isomerization.     

Ab Initio Study on the Anti-HIV Activities of Hydroxyflavones

1 INTRODUCTION AIDS, in other words, Acquired Immunodefici-encysyndrome, is a viral contagious disease withhigh death rate. However, effective treatment againstit has not appeared so far. At present, about 100kinds of natural compounds that could be extractedfrom natural products or artificially synthesized havebeen found to have anti-HIV activities to some ex-tent. They belong to flavonoid, terpenoid, steroid, cou-marin, peptide, alkaloid etc., respectively. Previousstudies show that…     

Hybrid Functional and Plane Waves based Ab Initio Molecular Dynamics Study of the Aqueous Fe2+/Fe3+ Redox Reaction**

Kohn-Sham density functional theory and plane wave basis set based ab initio molecular dynamics (AIMD) simulation is a powerful tool for studying complex reactions in solutions, such as electron transfer (ET) reactions involving Fe²⁺/Fe³⁺ ions in water. In most cases, such simulations are performed using density functionals at the level of Generalized Gradient Approximation (GGA). The challenge in modelling ET reactions is the poor quality of GGA functionals in predicting properties of such open-shell systems due to the inevitable self-interaction error (SIE). While hybrid functionals can minimize SIE, standard plane-wave based AIMD at that level of theory is typically 150 times slower than GGA for systems containing ∼100 atoms. Among several approaches reported to speed-up AIMD simulations with hybrid functionals, the noise-stabilized MD (NSMD) procedure, together with the use of localized orbitals to compute the required exchange integrals, is an attractive option. In this work, we demonstrate the application of the NSMD approach for studying the Fe²⁺/Fe³⁺ redox reaction in water. It is shown here that long AIMD trajectories at the level of hybrid density functionals can be obtained using this approach. Redox properties of the aqueous Fe²⁺/Fe³⁺ system computed from these simulations are compared with the available experimental data for validation.     

Ab initio Mechanism Study on the Reaction of Chlorine Atom with Formic Acid

The potential energy surface(PES) for the reaction of Cl atom with HCOOH is predicted using ab initio molecular orbital calculation methods at UQCIDS(T,full)6-311 G(3df,2p)//UMP2(full)/6-311 G(d,P) level of theory with zero-point vibrational energy (ZPVE) correction.The calculated results show that the reaction mechanism of Cl atom with formic acid is a C-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom with a 3.73kJ/mol reaction barrier height,leading to the formation of cis-HOCO radical which will reacts with Cl atom or other molecules in such a reaction system.Because the reaction barrier height of O-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom which leads to the formation of HCO2 radical is 67.95kJ/mol,it is a secondary reaction channel in experiment,This is in good agreement with the prediction based on the previous experiments.     

Ab Initio MP2 and Density Functional Theory Computational Study of AcAlaNH2 Peptide Hydration: A Bottom‐Up Approach

AcAlaNH₂?n H₂O (n=1–13) complexes have been proposed as models to account for water solvent effects on the molecular properties of N‐acetyl‐L ‐alanine amide. Ab initio computations are planned to evaluate peptide–water interactions and to provide a means for approximating relative effects of the short‐range many‐body interactions arising in real solution without introducing any external parameters intended to quantify empirical or semiempirical potential‐energy functions. The present bottom‐up approach reveals the formation of compact ring clusters of water molecules strongly bonded to peptidic polar groups throughout hydrogen bonds. The explicit coordination of water molecules around the peptide renders the fully extended (FE) and polyproline II (PPII) conformers more stable with respect to the 3₁₀ helix or γ turn. The alternance of donor and acceptor groups on both sides of the FE and PPII conformers allows for synergy and extensive H‐bonding.     

氟磺酸氟振动光谱的从头算

采用从头算HF／SCF方法以6-31G基组研究了FOSO2F分子的几何结构、振动谐性力场和红外光谱强度．理论力场由Pulay的标度量子力学方法进行标度,计算得到的振动频率与实验值比较平均偏差为6．3cm-1．根据振动频率的势能分布和从头算红外光谱强度值对此分子的振动基频进行了理论归属．     

Ab Initio and DFT Study of the Influence of the Allene Group on the Diels–Alder Reaction

Ab initio and DFT methods were used in combination with various basis sets in order to examine the [4 + 2] Diels–Alder cycloaddition reactions of ethene with 1,3-butadiene, 1,2,4-pentatriene, and 1,2,4,5-hexatetraene with a view to elucidating the role of the allene group in this type of pericyclic reaction. Based on the calculations, the insertion of an allene group decreases the activation energy and increases the exothermal character of the reaction. The decrease is even more marked in the presence of two allene groups, particularly with regard to the reaction enthalpy, which exhibits an additive effect.     

硫化钼微晶成键特性的ab initio研究

应用从头计算分子轨道方法,在HF／MINI／ECP和UHF／MINI／ECP水平上对Mo7S24^n-(n=0、1、2、3、4、6）六个硫化钼微昌体和加氢产物Mo7S24H12的几何构型进行了优化,通过对带电体系的能量分析选出三种有代表性的微晶：Mo7S24^2-、Mo7S24^-和Mo7S24,优化后的Mo7S24结构参数与实验值符合较好。在所研究的硫化钼微晶体中存在着三种不等价硫原子和两种不等价钼原子,计算结果表明,同种不等价原子的成键特征有明显差异,当体系带电及加氢时键级总能量有较大的变化,但形成键的杂化轨道类型却变化很小。     

卤代苯溶剂对镓咔咯配合物光物理性质的影响:外重原子效应

利用紫外-可见光谱、稳态和时间分辨荧光光谱以及飞秒瞬态吸收光谱探测了不同卤代苯溶剂对三种五氟苯基取代的镓咔咯(1-Ga、2-Ga、3-Ga)光物理性质的影响,结果表明卤代苯溶剂的色散力对于镓咔咯电子光谱吸收峰位置的影响起着主要作用;溶剂外重原子效应能显著降低镓咔咯的荧光量子产率。飞秒瞬态吸收光谱表明,光激发下,镓咔咯与卤代苯溶剂之间可发生电子转移反应,溶剂的重原子效应可以减缓电荷分离态复合物电荷重组速率。     

从头计算研究乙酰胆碱构象和分子静电势

在Hartree－Fock和二级Moller－Plesset微扰理论MP2水平，用6－31G对乙酰胆碱进行了从头计算研究，发现了旁式和反式两种稳定构象．经零点振动能校正后，在Hartree－Fock级别旁式较反式稳定0．24kJ·mol~(-1)；而在MP2级别，反式较旁式稳定2．07kJ·mol~(-1).谐振动频率在HF／6－31G水平计算.还给出了两种构象的MP2分子静电势图.     

Ab Initio Study on the Stability of NgnBe2N2, NgnBe3N2 and NgBeSiN2 Clusters

The global minima of Be₂N₂, Be₃N₂ and BeSiN₂ clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be₂N₂ and Be₃N₂ clusters and Ar?Rn binding to BeSiN₂ are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds.     

Ab Initio Study of the Adsorption of CO2 on Functionalized Benzenes

The interaction of carbon dioxide with a series of functionalized aromatic molecules was studied by using quantum mechanical methods (MP2), to examine the effect of the substituent on the adsorption of CO₂. Several different initial configurations of CO₂ were taken into account for each functionalized benzene to locate the energetically most favorable configuration. To get a better estimation of the binding energies, we applied an extrapolation scheme to approach the complete basis set. CH₂N₃‐, COOH‐, and SO₃H‐functionalized benzenes were found to have the strongest interaction with CO₂, and the corresponding binding energies were calculated to be ?3.62, ?3.65, and ?4.3 kcal mol^?1, respectively. Electrostatic potential maps of the functionalized benzenes and electron redistribution density plots of the complexes were also created to get a better insight into the nature of the interaction of CO₂ with the functionalized benzenes. The functional groups that were examined can be potentially incorporated in organic bridging molecules that connect the inorganic corners in MOF.     

NH2自由基与O3反应机理的从头计算

采用量子化学从头计算的UMP2(full)方法研究了NH2自由基与臭氧的反应机理，优化了反应物、中间体、过渡态和产物的几何构型，并做了频率分析.结果表明, NH2自由基与臭氧反应有两条反应通道，其中一条反应活化能很小，反应极易发生.化学反应热的计算结果与实验结果吻合较好.     

O与O2在Au团簇上吸附的密度泛函理论研究

采用基于密度泛函理论(DFT)的Dmol³程序系统研究了O原子与O₂在 Au₁₉与Au₂₀团簇上的吸附反应行为. 结果表明: O在Au₁₉团簇顶端洞位上的吸附较Au₂₀强; 在侧桥位吸附强度相近. O与O₂在带负电Au团簇上吸附较强, 在正电团簇吸附较弱. 从O―O键长看, 当金团簇带负电时, O―O键长较长, 中性团簇次之, 正电团簇中O―O键长较短, 因而O₂活化程度依次减弱. 电荷布居分析表明, Au团簇带负电时, O与O₂得电子数较中性团簇多, 而团簇带正电时, 得电子数较少. 差分电荷密度(CDD)表明, O₂与Au团簇作用时, 金团簇失电子, O₂的π^*轨道得电子, 使O―O键活化. O₂在Au₁₉^-团簇上解离反应活化能为1.33 eV, 较中性团簇低0.53 eV; 而在Au₁₉⁺上活化能为2.27 eV, 较中性团簇高0.41 eV, 这与O₂在不同电性Au₁₉团簇O―O键活化规律相一致.