用从头算研究Shilov反应的机理

Shilov反应在CH~4活化中占有中心地位,它有氧化加成和σ迁移两种可能的机理。本文用较大基组的从头算研究了这两种机理的反应过程,认为Shilov反应应按氧化加成机理进行。     

Ab initio study on the photochemical behavior of styrene

Ab initio complete active space self‐consistent field (CASSCF) and the second order multireference Møller‐Plesset calculations have been performed to examine the photochemical behavior of styrene upon the strong S₀‐S₂ electronic excitation in the low‐lying excited states. The optimized structure at the S₂/S₁ conical intersection (CIX) is characterized by a quinoid structure. The transition state (TS) in S₁ is in the vicinity of the S₂/S₁‐CIX. At the S₁‐TS, two reaction paths branch. One is the relaxation into the stable structure in S₁ and then emission into S₀. The other is the radiationless decay through the S₁/S₀‐CIX. © 2002 Wiley Periodicals, Inc. J Comput Chem 10: 950–956, 2002     

Ab initio intermolecular potential energy surface of He-LiH

The intermolecular potential energy surface of He-LiH complex was studied using the full-electronic complete forth-order Miller-Plesset perturbation (MPPT) method.In ab initio calculations,the bond length of LiH was fixed at 0 159 5 nm.The potential has two local minima of Vm=-179.93 cm for the linear He LiH geormetrv at Rm=0.227 nm and Vm=-10.44 cm-1 for the linear He-HL1 geometry at Rm=0.516 nm The potemal exhibits strong anisotropy The analytic potential function with 31 parameters was determined by fitting to the calculated ab,mtio potentials The influence of variation of LiH bond length on the potential energy surface was also studied     

Ab initio study of ice catalyzation of HOCl + HCl reaction

Experiments proved that the reaction of HOCl + HCl was very slow in the gas phase, but on ice surface it was rapid. In this work the ice catalysis of HOCl + HCl reaction was investigated by using ab initio molecular orbital theory. We applied the Hartree–Fock self‐consistent field and the second‐order Møller–Plesset perturbation theory with the basis sets of 6‐31G* to the model system. The complexes and transition state were obtained along the reaction with and without the presence of ice surface. By comparing the results, a possible catalyzation mechanism of ice on the reaction is proposed. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 281–284, 2000     

第一激发态HOOO裂解反应的理论研究

利用量子化学方法对第一激发态HOOO的裂解反应进行了理论研究.所有驻点(反应物、产物和过渡态)的几何结构优化和振动分析都是在CASSCF/6-31 G(d,p)理论水平下进行的.反应路径上的选择点及驻点都在CASPT2/6-31 G(d,p)//CASSCF(19,13)/6-31 G(d,p)和MRCI/6-31 G(d,p)//CASSCF(19,13)/6-31 G(d,p)理论水平下进行单点能量校正.CASSCF,CASPT2和MRCI水平的理论计算结果显示,第一激发态HOOO的裂解反应包含一个对称性变化的过程.它首先通过了一个Cs对称性的过渡态,然后逐渐变化为线性结构,最终生成产物O2(3Σg-)和OH(2Π).     

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.     

Ab initio reaction path for cisplatin interaction with L‐cysteine and L‐methionine

Ab initio calculations are used to track the reaction pathway of interaction between cisplatin and the sulfur‐containing amino acids cysteine (Cys) and methionine (Met). Structures of all reactive species as well as thermodynamic and kinetic properties were calculated and discussed based on the role played by the level of theory. Twenty‐three different levels of theory were examined including HF, DFT, and perturbation theory at MP2 and MP4(SDQ) orders. The rate constant for a second‐order associative ligand exchange mechanism (k₂) was calculated by means of transition state theory. This quantity is quite sensitive to small fluctuation of activation free energy, therefore is a good benchmark to assess the performance of different methods of calculations. The k₂ values predicted by DFT methods were in best agreement with experiment, found equal to (10²k₂ in M^?1 s^?1) 3.42 for Met (PBE1PBE) and 1.90 for Cys (B3P86). The experimental values are 3.6 and 2.2 for Met and Cys, respectively. The solvent effect plays a primary role to the kinetic properties, accounting for ～30% of the activation Gibbs free energy. The outcomes from the present study promptly show the adequacy of distinct theoretical approaches to describe the reactivity of cisplatin, thus might be useful for further studies involving other Pt(II) complexes. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Benzooxirene. Ab initio calculations

Ab initio calculations have been performed on benzooxirene, the corresponding oxo carbene (“ketocarbene”), and the transition state linking the two. At the highest level used, QCISD(T)/6-31G^*//MP2(FULL)/6-1G^* with MP2(FULL)/ 6-31G^* zero point energy corrections, the relative energies of the oxirene, the transition state and the carbene are 0, 24.6, and −17.8 kJ mol⁻¹. Correlation energy effects are very important in this system: at the QCISD(T) level the oxirene lies above the carbene, as at the MP4 and HF levels, but at the MP2 level the ordering is reversed. Benzooxirene is probably slightly nonplanar: the HF/6-31G^* geometry is C_2v but the MP2(Fermi contact)/6-31G^* geometry is C_s with a 6-/3-ring coplanarity deviation of about 6.9 °, although in the MP2(FULL)/6-31G^* geometry this is reduced to about 3.1 °.     

Ab initio studies of peroxynitrite anion-water complexes

Quantum mechanical methods have been applied to thecis-ONOO^–-H₂O,cis-ONOO^–-(H₂O)₂ andtrans- ONOO^–-H₂O complexes. Equilibrium geometries, binding energies, net atomic charges and vibrational frequencies are presented for several different arrangements. The MØller-Plessett second-order perturbation (MP2) method predicted shorter hydrogen bonds than the SCF method, but the computed Hartree-Fock (HF) binding energies are similar to counterpoise corrected MP2 values. The geometry changes of ONOO^– and water after solvation are examined. The ONOO^– and H₂O bond length changes follow typical hydrogen bond structural trends, whereas bond angles in ONOO^– are unaffected when the hydrogen bond is formed, similar to the conclusions from NO ₂ ^– -(H₂O) _n HF/6-31G studies and Monte Carlo simulations. Thecis-ONOO^–-(H₂O) _n frequencies are compared with the solution Raman spectrum and with calculations on isolated ONOO^–.     

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。     

Ab initio study on the electronic structures of styrene in the Franck-Condon region

The electronic structures of styrene in the Franck‐Condon region have been theoretically examined by means of ab initio complete active space self‐consistent field (CASSCF) and the second order multireference Møller‐Plesset calculations. The optimized structure of styrene in S₀ is planar but the torsional motion of the phenyl group is very floppy. The S₁ state is assigned to the local π–π* excitation within the benzene ring. On the other hand, S₂, above S₁ by 0.561 eV, is assigned to a state that resembles the so‐called V‐state of ethylene. The transition intensity of S₀–S₁ is weak, while that of S₀–S₂ is strong. This is in good agreement with the experimental absorption spectrum where the S₀–S₁ and S₀–S₂ transitions are in the energy range of 290–220 nm. The optimized geometry of S₁, characterized by an enlarged benzene ring and its vibrational analyses, further justifies the assignment of the S₁ state. © 2002 Wiley Periodicals, Inc. J Comput Chem 9: 928–937, 2002     

Ab initio studies for the photodissociation mechanism of hydroxyacetone

The reaction pathways for CH(3)COCH(2)OH (hydroxyacetone) photodissociation on the low-lying electronic states have been studied with use of the CASSCF energy gradient techniques. The S(0)/S(1) and S(1)/T(1) intersection points were determined by the state-average CASSCF method. Two main reaction pathways, which are possible to the photodissociation, have been studied. It has been found that the mechanism is stepwise, and belongs to Norrish type-I reaction. The n --> pi* excitation leads to the first excited singlet state, followed by the intersystem crossing from S(1) to T(1). On the T(1) potential energy surface, the system can dissociate adiabatically to CH(3)(x) +COCH(2)OH( x) and CH(3)CO(x)+CH(2)OH(x). The COCH(2)OH(x) and CH(3)CO(x) radicals can further dissociate into CO, OH, and other fragments. Our calculated results are in good agreement with recent experimental results.     

Ab initio study on structures and stabilities of OLi n hyperlithiated compounds

The geometries of hyperlithiated compounds OLi_n were optimized by means of HF, MP2 and DFT methods with 6-31G basis set. The dissociation energies of those optimized stable geometries of OLi_n were calculated, the results are in good agreement with experimental values; and moreover, the dissociation energy of OLi_6 is predicted. In addition, the fundamental vibrational frequencies were also predicted.     

Ab initio fragment orbital‐based theory

A new formulation of ab initio theory is presented that treats a large molecule in terms of wave functions of its constituent molecular subunits (to be called fragments). The method aims to achieve near conventional ab initio accuracy but using a truncated set of fragment orbitals with a consequent drastic reduction of computing time and storage requirement. Illustrative calculations are presented for the molecule amino‐nitro‐stilbene. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

2-苯基苯并咪唑衍生物非线性光学性质的从头算研究

采用HF／6-31G^*方法优化分子构型，在此基础上用CPHF方法系统地研究了多种基团取代的2-苯基苯并咪唑衍生物的二阶非线性光学系数βvec，并对βvdc的影响因素进行了探讨，为进一步设计综合性能优良的有机非线性光学材料提供理论指导．     

Ab initio study of the transition-metal carbene cations

The geometries and bonding characteristics of the first-row transition-metal carbene cations MCH_2~ were investigated by ab initio molecular orbital theory (HF/LANL2DZ). All of MCH_2~ are coplanar. In the closed shell structures the C bonds to M with double bonds; while in the open shell structures the partial double bonds are formed, because one of the σ and π orbitals is singly occupied. It is mainly the π-type overlap between the 2p_x orbital of C and 4p_x, 3d_(xz), orbitals of M~ that forms the π orbitals. The dissociation energies of C—M bond appear in periodic trend from Sc to Cu. Most of the calculated bond dissociation energies are close to the experimental ones.     

Ab initio study on the mechanism of reaction HNCO+NH_2

Ab initio UMP2 and UQCISD(T) calculations, with 6-311G** basis sets, were performed for the titled reactions. The results show that the reactions have two product channels: NH2+ HNCO→NH3+NCO (1) and NH2+HNCO-N2H3+CO (2), where reaction (1) is a hydrogen abstraction reaction via an H-bonded complex (HBC), lowering the energy by 32.48 kJ/mol relative to reactants. The calculated QCISD(T)//MP2(full) energy barrier is 29.04 kJ/mol, which is in excellent accordance with the experimental value of 29.09 kJ/mol. In the range of reaction temperature 2300-2700 K, transition theory rate constant for reaction (1) is 1.68 × 1011- 3.29 × 1011 mL · mol-1· s-1, which is close to the experimental one of 5.0 ×1011 mL× mol-1· s-1 or less. However, reaction (2) is a stepwise reaction proceeding via two orientation modes, cis and trans, and the energy barriers for the rate-control step at our best calculations are 92.79 kJ/mol (for cis-mode) and 147.43 kJ/mol (for trans-mode), respectively, which is much higher than     

Ab initio study of the reaction path of the reaction HNCO+CN

HNCO is a convenient photolytic source of NCO and NH radicals for laboratory kinetics studies of elementary reaction[1] and plays an important role in the combustion and atmosphere chemistry. It can re- move deleterious compounds rapidly from exhausted ga…     

Ab initio static and molecular dynamics study of 4-styrylpyridine.

We report an in‐depth theoretical study of 4‐styrylpyridine in its singlet S₀ ground state. The geometries and the relative stabilities of the trans and cis isomers were investigated within density functional theory (DFT) as well as within Hartree–Fock (HF), second‐order Møller–Plesset (MP2), and coupled cluster (CC) theories. The DFT calculations were performed using the B3LYP and PBE functionals, with basis sets of different qualities, and gave results that are very consistent with each other. The molecular structure is thus predicted to be planar at the energy minimum, which is associated with the trans conformation, and to become markedly twisted at the minimum of higher energy, which is associated with the cis conformation. The results of the calculations performed with the post‐HF methods approach those obtained with the DFT methods, provided that the level of treatment of the electronic correlation is high enough and that sufficiently flexible basis sets are used. Calculations carried out within DFT also allowed the determination of the geometry and the energy of the molecule at the biradicaloid transition state associated with the thermal cis?trans isomerization and at the transition states associated with the enantiomerization of the cis isomer and with the rotations of the pyridinyl and phenyl groups in the trans and cis isomers. Car–Parrinello molecular dynamics simulations were also performed at 50, 150, and 300 K using the PBE functional. The studies allowed us to evidence the highly flexible nature of the molecule in both conformations. In particular, the trans isomer was found to exist mainly in a nonplanar form at finite temperatures, while the rotation of the pyridinyl ring in the cis isomer was incidentally observed to take place within ≈1 ps during the simulation carried out at 150 K on this isomer.     

1,2方酸衍生物非线性光学性质的从头算研究

用CPHF方法在abinitio/4-31G+pd水平上计算了四个1,2方酸衍生物分子的线性极化率,一阶和二阶超极化率.从电荷分布,跃迁偶极矩,前沿轨道性质等方面讨论了其结构与性能的关系.研究表明,四元环作为吸电基团(A),取代基作为供电基团(D),组成了D-A-D结构,取代基的性质对分子的非性光学系数有显著影响.