甲醛与甲酸相互作用的从头算研究

在MP2／6—31G(d)和MP2(FC)／6—311 G(d，p)水平上，对H2CO和HCOOH以及设计的4种构型H2CO…HCOOH复合物等进行几何全优化计算，经振动频率分析，确认它们为势能面上的稳定驻点．然后在MP2／6—311 G(2df，2p)水平上进行单点能计算和基组重叠误差(BSSE)校正以获得相互作用能，并利用自然键轨道理论探讨H2CO和H(X)OH相互作用的本质。     

CHF_3与O(~3P)反应机理的理论研究

采用从头算MP2/6-311G(d,p)方法研究了CHF3与O(3 P)的反应机理,优化了所有反应物、产物和过渡态的几何构型,并通过振动频率分析和内禀反应坐标(IRC)方法确证了过渡态的真实性.在QCISD(T)/6-311++G(d,p)水平上精确计算了各反应物种的单点能.结果表明,标题反应共存在4类反应,分别为抽提氢反应(R1)、抽提氟反应(R2),消氟化氢反应(R3)和消氢反应(R4),在QCISD(T)/6-311++G(d,p)//MP2/6-311G(d,p)水平上,R1,R2,R3和R4反应的能垒分别为70.7,378.7,294.7和307.2kJ·mol-1,抽提氢反应为主反应通道.     

高级量子化学从头计算法研究N2和H2O分子间相互作用

在MP2/6-311++G(3d,3p)电子相关校正水平上,对N₂和H₂O分子间可能存在的氢键复合物进行全自由度能量梯度优化,发现了一个接近于直线的弱氢键总能量极小结构(1),进一步在高级电子相关校正的MP4SDTQ和CCSD(T)水平,用6-311++G(3d,3p)基组加上(3s3p2d1f)键函数,用MP4和CCSD(T)计算的结构1的结合能分别为-5.061kJ/mol和-4.715kJ/mol.     

硫代甲酰胺双聚体的量子化学计算

在MP2/6 31G(d)和MP2(FC)/6 311 G(d,p)水平上,对硫代甲酰胺(HC-SNH2)及其3种构型双聚体进行几何全优化计算,经振动频率分析,确认为势能超曲面上的稳定驻点.然后在MP2/6 311 G(2df,2p)水平上进行单点能计算和基组重叠误差(BSSE)校正以获得相互作用能.并利用自然键轨道(NBO)理论和分子中的原子(AIM)理论探讨HCSNH2之间相互作用的本质.     

CH2=CHCl与O(3P)反应的理论研究

用量子化学密度泛函理论和QCISD(Quadratic configuration interaction calculation)方法,对0(^3P)与CH2CHCl的反应进行了理论研究．在UB3LYP／6—311 G(d,p),UB3LYP／6—31 (3df,3pd)计算水平上,优化了反应物、产物、中间体和过渡态的几何构型,并在UQCISD(T)／6—311 G(2df,2pO)水平上计算了单点能量．为了确证过渡态的真实性,在UB3LYP／6—311 G(3df,3pd)水平上进行了内禀坐标(IRC)计算和频率分析,并确定了反应机理．研究结果表明,反应主要产物为CH2CHO和Cl．     

GeH4与HX(X＝F,Cl,Br)间二氢键复合物的理论研究

对GeH4与HX形成的二氢键复合物的结构特征及本质进行了探讨.在MP2/6-311 ++G(3 d,3p)水平优化、频率验证得到复合物的分子结构,通过分子的几何参数及电子密度拓扑分析,确认GeH4与卤化氢已形成了二氢键复合物.MP2/6-311 ++ G(3d,3p)水平下进行BSSE校正后的结合能为3.281到4.5...     

C2H3和NO2反应势能面的理论研究

在CCSD(T)／6—311G(d，p)／／B3LYP／6—3llG(d，p)水平上给出了反应C2H3 NO2的详细势能面信息，并列出了中间体和过渡态的几何构型．通过深入分析反应路径及反应机理，得到5个能量可行的产物和6条反应通道，其中产物C2H3O NO的形成又有利，而产物CH2CO HNO则是次要产物，其他产物在通常条件下可以忽略．     

已烯自由基阳离子的密度泛函理论研究

使用密度泛函理论B3LYP方法和6-31G(d,p),6-31+G(d,p),6-311G(d,p)及6- 311+G(d,p)基组，分别对1-C_6H_(12)~+,2-C_6H_(12)~+和3-C_6H_(12)~+的各种构 象进行了几何构型优化，并在B3LYP/6-311G(d,p)水平上进行了频率分析计算，在 各优化构型上，使用B3LYP和MP2(full)方法进行了超精细结构的计算。计算的3- C_6H_(12)~+的超精细偶合常数比以往的计算结果更好；1-C_6H_(12)~+和2-C_6H_ (12)~+的超精细偶合常数目前尚无实验数据报道，本计算预言了它们的超精细偶合 常数和最稳定构型。     

丁烯和丁烷自由基阳离子的分子结构和超精细结构的 理论研究

用密度函数理论B3LYP方法和6-31G(d,p),6-311G(d,p)及6-311+G(d,p)基组，分别对1-C4H^+~8,2-C4H^+~8和C4H^+~10进行了构型优化和频率分析计算，预言1-C4H^+~8具有非平面构型，与以往报道的从头算和密度函数理论计算结果不同。在各自由基阳离子的B3LYP构型上，进行了B3LYP、MP2及MRSDCI方法的超精细偶合常数计算，得到了比以往更好的结果，特别是MP2/B3LYP计算值是至今与实验值符合得最好的理论计算结果。     

HBO2异构体的结构和相对稳定性

用ab initio方法在MP2/6 311＋＋G(d,p)水平下优化得到了HBO2体系的若干异构体和过渡态，并在QCISD(t)/6 311＋＋G(3df,2p)//MP2/6 311＋＋G(d,p)水平下进行了单点能量校正.对计算结果的分析表明，无论是在热力学还是在动力学上，具有链状结构的HOBO异构体(E1)是势能面上最稳定的结构，并对E1的电子结构进行了分析；另一具有C2v对称性的HBO(O)结构的异构体(E2)的能量比E1高381.72 kJ•mol－1，由于E2处于一个较深的势垒中，因此是比较稳定的，可以推断，在适合的实验中应该可以观察到异构体E2.     

Theoretical study on the hydrogen abstraction reaction of CH3CH2F (HFC-161) with Cl atom

A direct dynamics method is employed to study the hydrogen abstraction reaction of CH₃CH₂F+Cl. Three distinct transition states are located, one for -H abstraction and two for β-H abstraction. The potential energy surface (PES) information is obtained at the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p), CCSD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) and G2//MP2/6-311G(d,p) level. Based on the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) results, the rate constants of the three reaction channels are evaluated by using the canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over the temperature range of 220–2800 K. The calculated results indicate that -H abstraction dominates the total reaction almost over the whole temperature range.     

A computational study of intramolecular proton transfer in gaseous protonated glycine

The minimum energy paths for intramolecular proton transfer between the amino nitrogen and carbonyl oxygen atoms in gaseous protonated glycine were estimated at the Hartree-Fock (HF) and second-order M?ller-Plesset Perturbation (MP2) levels of theory. Potential energy profiles and their associated reactant, transition state, and product species calculated at the MP2/6-31G* level were shown to differ significantly from those obtained at the HF/6-31G* level. Effects of electron correlation and basis functions on the calculated geometries and energies of relevant species were examined at the HF, MP2, MP4, CCSD, and B3LYP levels using the 6-31G*, 6-31G**, 6-31+G**, 6-311+G**, 6-31+G(2d,2p), 6-311+G(3df,2p), cc-pVDZ, aug-cc-pVDZ, and cc-pVTZ basis sets. The HF and MP2 optimized levels with the 6-31G*, 6-31G**, 6-31+G**, and 6-311+G** bases were used to calculate the thermodynamic and kinetic properties of the proton transfer reaction at 298.15 K and 1 atm, which include enthalpy, entropy, Gibbs free energy, equilibrium constant, potential energy barriers, tunneling transmission coefficients, and rate constants. Results indicate that the proton in a carbonyl O-protonated glycine undergoes a rapid migration to the amino nitrogen atom, while the reverse process is extremely unfavorable. The objective of this work is to develop practical theoretical procedures for studying proton transfer reactions in amino acids and peptides and to assemble physical data from these model calculations for future references.     

Direct dynamic study on the hydrogen abstraction reaction CH3CN + OH-->CH2CN + H2O

The reaction of acetonitrile with hydroxyl has been studied using the direct ab initio dynamics methods. The geometries, vibrational frequencies of the stationary points, as well as the minimum energy paths were computed at the BHandHLYP and MP2 levels of theory with the 6-311G(d, p) basis set. The energies were further refined at the PMP4/6-311+G(2df, 2pd) and QCISD(T)/6-311+G(2df, 2pd) levels of theory based on the structures optimized at BHandHLYP/6-311G(d, p) and MP2/6-311G(d, p) levels of theory. The Polyrate 8.2 program was employed to predict the thermal rate constants using the canonical variational transition state theory incorporating a small-curvature tunneling correction. The computed rate constants are in good agreement with the available experimental data.     

Modern valence-bond description of chemical reaction mechanisms: the 1,3-dipolar addition of diazomethane to ethene

The electronic mechanism for the gas-phase concerted 1,3-dipolar cycloaddition of diazomethane (CH2N2) to ethene (C2H4) is described through spin-coupled (SC) calculations at a sequence of geometries along the intrinsic reaction coordinate obtained at the MP2/6-31G(d) level of theory. It is shown that the bonding rearrangements occurring during the course of this reaction follow a heterolytic pattern, characterized by the movement of three well-identifiable orbital pairs, which are initially responsible for the pi bond in ethene and the C-N pi bond and one of the N-N pi bonds in diazomethane and are retained throughout the entire reaction path from reactants to product. Taken together with our previous SC study of the electronic mechanism of the 1,3-dipolar cycloaddition of fulminic acid (HCNO) to ethyne (C2H2) (Theor. Chim. Acc. 1998, 100, 222), the results of the present work suggest strongly that most gas-phase concerted 1,3-dipolar cycloaddition reactions can be expected to follow a heterolytic mechanism of this type, which does not involve an aromatic transition state. The more conventional aspects of the gas-phase concerted 1,3-dipolar cycloaddition of diazomethane to ethene, including optimized transition structure geometry, electronic activation energy, activation barrier corrected for zero-point energies, standard enthalpy, entropy and Gibbs free energy of activation, have been calculated at the HF/6-31G(d), B3LYP/6-31G(d), MP2/6-31G(d), MP2/6-31G(d,p), QCISD/6-31G(d) and CCD/6-31G(d) levels of theory. We also report the CCD/6-311++G(2d, 2p)//CCD/6-31G(d), MP4(SDTQ)/6-311++G(2d,2p)//CCD/6-31G(d) and CCSD(T)/6-311++G(2d, 2p)//CCD/6-31G(d) electronic activation energies.     

Theoretical study and rate constant computation on the reaction HFCO + OH --> CFO + H2O

The potential energy surface, including the geometries and frequencies of the stationary points, of the reaction HFCO + OH is calculated using the MP2 method with 6-31+G(d,p) basis set, which shows that the direct hydrogen abstraction route is the most dominating channel with respect to addition and substitution channels. For the hydrogen abstraction reaction, the single-point energies are refined at the QCISD(T) method with 6-311++G(2df,2pd) basis set. The calculated standard reaction enthalpy and barrier height are -17.1 and 4.9 kcal mol(-1), respectively, at the QCISD(T)/6-311++G(2df,2pd)//MP2/6-31+G(d,p) level of theory. The reaction rate constants within 250-2500 K are calculated by the improved canonical variational transition state theory (ICVT) with small-curvature tunneling (SCT) correction at the QCISD(T)/6-311++G(2df,2pd)//MP2/6-31+G(d,p) level of theory. The fitted three-parameter formula is k = 2.875 x 10(-13) (T/1000)1.85 exp(-325.0/T) cm(3) molecule(-1) s(-1). The results indicate that the calculated ICVT/SCT rate constant is in agreement with the experimental data, and the tunneling effect in the lower temperature range plays an important role in computing the reaction rate constants.     

An Ab Initio Study of the Complexes Formed by the Positive Acetylene Ion with the Hydrogen and Nitrogen Molecules and the Argon Atom

The complexes formed by the positive acetylene ion with the hydrogen molecule, the nitrogen molecule, and the argon atom are investigated with ab initio calculations using the 6-311G** and the 6-31+G(2df,2pd) basis sets. MP2/6-311G** energies and optimum geometries are obtained, as well as single-point MP3, MP4, and QCISD(T) energies with the MP2/6-311G** optimized geometries. Single-point calculations are performed with the 6-31+G(2df,2pd) basis set at MP2/6-311G** optimized geometries.     

Transition state structure and energetics of the N(2)O + X (X = Cl,Br) reactions

The structural and vibrational properties of the transition state of the N(2)O + X (X = Cl,Br) reactions have been characterized by ab initio methods using density functional theory. We have employed Becke's hybrid functional (B3LYP), and transition state optimizations were performed with 6-31G(d), 6-311G(2d,2p), 6-311+G(3d,2p), and 6-311+G(3df,2p) basis sets. For the chlorine atom reaction the coupled-cluster method (CCSD(T)) with 6-31G(d) basis set was also used. All calculations resulted in transition state structures with a planar cis arrangement of atoms for both reactions. The geometrical parameters of transition states at B3LYP are very similar, and the reaction coordinates involve mainly the breaking of the N-O bond. At CCSD(T)/6-31G(d) level a contribution of the O-Cl forming bond is also observed in the reaction coordinate. In addition, several highly accurate ab initio composite methods of Gaussian-n (G1, G2, G3), their variations (G2(MP2), G3//B3LYP), and complete basis set (CBS-Q, CBS-Q//B3LYP) series of models were applied to compute reaction energetics. All model chemistries predict exothermic reactions. The G3 and G2 methods result in the smallest deviations from experiment, 1.8 and 0 kcal mol(-1), for the enthalpies of reaction for N(2)O reaction with chlorine and bromine, respectively. The G3//B3LYP and G1 methods perform best among the composite methods in predicting energies of the transition state, with a deviation of 1.9 and 3.0 kcal mol(-1), respectively, in the activation energies for the above processes. However, the B3LYP/6-311+G(3df,2p) method gives smaller deviations of 0.4 and -1.0 kcal mol(-1), respectively. The performance of the methodologies applied in predicting transition state energies was analyzed.     

分子几何构型优化方法的系统性比较

对《ＣＲＣ物理化学手册》第７７版中收集的第三周期以前的所有已知实验构型的无机分子的构型,以ＭＰ２、Ｂ３ＬＹＰ、Ｂ３ＰＷ９１级别上进行了构型优化的系统性比较,优化采用基组为６－３１Ｇ（ｄ,ｐ）,６－３１１Ｇ（ｄ,ｐ）,６－３１１Ｇ（２ｄ,ｐ）。对大多数分子另比较了ＱＣＩＳＤ（Ｔ）方法,对多原子分子比较了ＢＰＷ９１方法,对含氢双原子分子也使用ＱＣＩＳＤ方法。结果表明,键长的平均绝对偏差（单位：ｐｐｍ）     

Infrared and Raman spectra, conformational stability, ab initio calculations and vibrational assignments for trans-3-chloropropenoyl chloride

The infrared (3500-30 cm(-1)) spectra of gaseous and solid and the Raman (3500-200 cm(-1)) spectra of the liquid with quantitative depolarization ratios and solid trans-3-chloropropenoyl chloride (trans-ClCHCHCClO) have been recorded. These data indicate that both the anti (carbonyl bond trans to the carbon-carbon double bond) and syn conformers are present in the fluid states but only the anti conformer is present in the crystalline state. The mid-infrared spectra of the sample dissolved in liquid xenon as a function of temperature (-55 to -100 degrees C) have been recorded. Utilizing conformer pairs at 870 and 725 cm(-1), 1215 and 1029 cm(-1), and 1215 and 1228 cm(-1), the enthalpy difference has been determined to be 136+/-5 cm(-1) (389+/-14 cal mol(-1)) with the anti conformer the more stable form. Optimized geometries and conformational stabilities were obtained from ab initio calculations at the levels of RHF/6-31G(d), MP2/6-31G(d), MP2/6-311 + + G(d,p), MP2/6-311 + + G(2d,2p) and MP2/6-311 + + G(2df,2pd) with only the latter two calculations predicting the anti rotamer to be the more stable form. The vibrational frequencies, harmonic force constants and infrared intensities were obtained from the MP2/6-31G(d) calculations, whereas the Raman activities and depolarization values were obtained from the RHF/6-31G(d) calculations. The spectra are interpreted in detail and the results are compared with those obtained for some related molecules.     

Molecular Dipole Moment Computed with Ab Initio MKS Charges

1 INTRODUCTION Dipole moment (DM) can be measured by a variety of experimental methods[1] or computed with atomic charge distribution directly derived from molecular orbital calculations[2~10]. The average errors in DM computed with AM1, PM3 and MNDO methods for 125 organic compounds are 0.35 D, 0.45 D and 0.45 D, respectively[2]. Feller et al. reported that the average errors in the computed DM at the HF level are 0.65 D, 0.49 D and 0.30 D with the basis set STO-3G, 3-21G and…