Rg—HX(Rg=He,Ne;X=F,Cl,Br)分子间势的精确量子化学从头计算研究III.He—HBr

在用非迭代的三重激发项来校正CCSD的CCSD（T）理论水平下,采用aug-cc- pVQZ基函数对He—HBr的分子间势进行了系统的研究。结果表明：He—HBr以线型结 构存在。在极限基的情况下,复合物两种线型极小点结构He—H—Br和He—Br—H势 阱深分别为28.792 cm~(-1)和35.707 cm~(-1),对应He原子到HBr分子质心的距离 R分别为0.407 nm和0.343 nm。讨论了不同的基函数和理论方法在研究此类弱束缚 态复合物的分子间势时的可靠性及其对结果的影响,同时也给出了热函数的解析形 式。     

Rg—HX(Rg=He,Ne;X=F,Cl,Br)分子间势的精确量子化学从头计算研究III.He—HBr

在用非迭代的三重激发项来校正CCSD的CCSD（T）理论水平下，采用aug-cc- pVQZ基函数对He—HBr的分子间势进行了系统的研究。结果表明：He—HBr以线型结 构存在。在极限基的情况下，复合物两种线型极小点结构He—H—Br和He—Br—H势 阱深分别为28.792 cm~(-1)和35.707 cm~(-1)，对应He原子到HBr分子质心的距离 R分别为0.407 nm和0.343 nm。讨论了不同的基函数和理论方法在研究此类弱束缚 态复合物的分子间势时的可靠性及其对结果的影响，同时也给出了热函数的解析形 式。     

[He3H]＋分子基态势能面的从头计算研究

使用CCSD(T)/aug-cc-pVTZ从头计算方法，对[He3H]＋分子的一些特殊构型的电子基态势能进行扫描，并以此为基础对三体相互作用势在惰性气体质子簇中的影响进行了讨论.结果表明即使在这样一个简单的体系中三体相互作用的影响都是不能忽略的.另一方面，在[He3H]＋分子稳定构型附近仅将势能展开至三体相互作用项便可提供较精确的相互作用信息，但在强排斥区域更高阶作用的影响变得越来越突出.本文同时讨论了[He4H]＋的稳态结构. [He3H]＋与[He4H]＋的稳态结构表明,[HenH]＋簇中存在着一个[He2H]＋核.     

He2F-体系的分子间相互作用势能面

使用高水平的从头算CCSD(T)/aug-cc-pVTZ方法, 经过Counterpoise校正, 计算了He2F-体系的分子间相互作用势能面. 在He2F-体系的相互作用势能面的最小值处, 发现了一个等腰三角形的稳定结构. 在这个结构中, He…F- 距离是 0.334 nm, He…He 的距离是 0.295 nm, ∠HeF-He 为 52.5°. 计算了此稳定结构的频率、相互作用能、二体相互作用能和三体相互作用能. 在CCSD(T)/d-aug-cc-pVTZ水平下, 相互作用能为-1.727 kJ/mol.     

HF分子与惰性气体二聚体的分子形貌的理论研究

采用Gaussian-03程序中的MP2/6-311++G(2d,2p)方法,优化了FH- Rg(Rg=He,Ne,Ar)二聚体的结构.使用MELD精密从头计算中的CISD方法,结合我们自编的程序,计算了这些二聚体的单电子作用势(PAEM),并绘出了它们的分子形貌图象.分子形貌所提供的形貌特征、前沿电子密度的特征等,可以直观地揭示He,Ne和Ar等原子与HF分子相互作用时2种相互作用的差别,即共价相互作用与非共价相互作用区分的直观形象的表征.从二聚体的内禀特征信息可以看出,F,H和Rg原子都发生了不同程度的变形,HF分子对惰性气体原子有一定影响,而惰性气体原子对HF分子的影响较小.     

F-+CH3Cl→CH3F+Cl-反应过程中的分子形貌变化

双分子亲核(SN2)反应是重要的基本有机反应之一,其中电子从亲核基团向离去基团的转移发挥着关键作用.利用从头计算方法CCSD(T)/aug-cc-pVDZ和我们发展的分子形貌理论,对反应F-+CH3Cl→CH3F+Cl-进行了研究,给出了反应过程中分子形状和电子转移的动态变化图像.结果表明,沿内禀反应坐标,从反应开始到生成反应前复合物,亲核试剂F-的分子内禀特征轮廓在缓慢收缩,而其上的电子密度在缓慢增大.此后,F的轮廓迅速膨胀,电子密度急剧下降,尤其是从过渡态到产物复合物的过程中.而在反应过程中,离去基团Cl的轮廓一直在收缩,其上的电子密度一直在增大.对反应过程中电子所受到作用势的研究表明,随着反应的进行,电子在F与C间受到的作用势逐渐降低,而在C与Cl间受到的作用势逐渐升高,清楚地展现反应过程中F与C间化学键生成和C与Cl间化学键断裂的动态过程.     

PdH2、YH2分子的结构与势能函数

用密度泛函理论的B3LYP方法,对钯和钇原子采用SDD收缩价基函数,氢原子采用6-311＋＋G**全电子基函数,对PdH2和YH2体系的结构进行优化计算,得到PdH2分子最稳态为C2v构型,电子组态为1A1,平衡核间距RPdH=0.1692 nm,键角∠HPdH=29.4°,离解能De=5.5212 eV,基态简正振动频率:ν1(b2)=1470.1 cm－1、ν2(a1)=1007.9 cm－1、ν3(a1)=2907.0 cm－1.YH2分子最稳态也为C2v构型,电子组态2A1,RYH=0.1962 nm,∠HYH=114.3°,De=5.6691 eV,基态简正振动频率:ν1(b2)=1457.9 cm－1、ν2(a1)=476.0 cm－1、ν3(a1)=1506.3 cm－1.由微观过程的可逆性原理分析了分子的可能离解极限.并用多体项展式理论方法分别导出基态PdH2和YH2分子的势能函数,其等值势能面图准确地再现了PdH2和YH2分子的结构特征和离解能,由此讨论了Pd ＋ H2和Y ＋ H2分子反应的势能面静态特征.     

氟代乙烯阳离子的理论研究

用B3LYP和MP2方法及6-31G(d, p)、6-31＋G(d, p)、6-311G(d, p)和6-311＋G(d, p) 基组，对六种氟代乙烯阳离子做了理论研究，优化了它们的基电子态的结构，计算了对应分子的垂直电离势（VIP）和绝热电离势(AIP).结果表明，与具有非平面结构的乙烯阳离子不同，六种氟代乙烯阳离子都只具有平面结构；与分子结构相比，离子结构的C－C键增长， C－F键缩短， CCF键角变小. 自然布居分析计算表明，这些离子的正电荷主要分布在与F原子相连的C原子和各H原子上. B3LYP/6-311＋G(d, p) 级别上计算的各分子的VIP和AIP值和实验值符合得很好. 使用含弥散基函数的基集可以明显提高这类分子的电离势的计算精度.     

二阶多参考态微扰理论计算电子亲和势

采用二阶多参考微扰理论计算了F, Cl, OH, SH, CN, CH₂和NH₂的电子亲和势.另外,还考察了基函数和完全活性空间大小对电子亲和势精度的影响.通过和CASSCF, CASPT2, CCSD, CCSD(T), B3LYP, X3LYP, M06, HCTH, TPSS, B97D3, mPW2PLYP和B2PLYP的计算结果比较发现,针对目前所用的基函数,二阶多参考态微扰理论的总体计算效果是最好的.     

噻吩与6种氢化物相互作用本质的从头算MP2研究

在从头算MP2/aug-cc-pVDZ理论水平上,研究了6种典型氢化物HnX（HCl、HF、H2O、H2S、NH3、PH3）与杂芳环噻吩（C4H4S）分子形成复合物的几何形状及其相互作用的本质。寻找到C4H4S与小分子氢化物形成的π型优势噻吩复合物。用对称匹配微扰理论（SPTA）和自然键轨道（NBO）理论,分析了该系列复合体系的能量及其分项。SPTA模拟计算结果表明,C4H4S系列6种小分子氢化物复合体系间的静电作用能和色散作用能贡献较大,是关键项,而分子间的诱导作用能的贡献占比较小。其中当X=F或O原子时,分子间静电相互作用能分项占比稍占优势,而当X=N,Cl,S和P原子时,则分子间色散相互作用能分项稍占优势。自然键轨道理论和电子局域密度函数图也支持以上结论。     

Theoretical study of potential energy surface and vibrational spectra of ArF2 system

An ab initio potential energy surface (PES) of ArF2 system has been obtained by using MP4 calculation with a large basis set including bond functions. There are two local minimums on the PES: one is T-shaped and the other is L-shaped. The L-shaped minimum is the global minimum with a well depth of -119.62 cm- 1 at R = 0.3883nm. The T-shaped minimum has a well depth of -85.93cm -1 at R = 0.3486 nm. A saddle point is found at R = 0.3486 and θ = 61° with the well depth of -61.53 cm-1. The vibrational energy levels have been calculated by using VSCF-CI method. The results show that this PES supports 27 vibrational bound states, and the ground states are two degenerate states assigned to the L-type vibration.     

Theoretical study of potential energy surface and vibrational spectra of ArF2 system

Anab initio potential energy surface (PES) of ArF₂ system has been obtained by using MP4 calculation with a large basis set including bond functions. There are two local minimums on the PES: one is T-shaped and the other is L-shaped. The L-shaped minimum is the global minimum with a well depth of -119.62 cm^-1 atR = 0.3883nm. The T-shaped minimum has a well depth of -85.93cm^-1 atR = 0.3486 nm. A saddle point is found atR = 0.3486 and τ = 61° with the well depth of -61.53 cm^-1. The vibrational energy levels have been calculated by using VSCF-CI method. The results show that this PES supports 27 vibrational bound states, and the ground states are two degenerate states assigned to the L-type vibration.     

Evidence for excited spin-orbit state reaction dynamics in F+H2: theory and experiment

We describe fully quantum, time-independent scattering calculations of the F+H2-->HF+H reaction, concentrating on the HF product rotational distributions in v'=3. The calculations involved two new sets of ab initio potential energy surfaces, based on large basis set, multireference configuration-interaction calculations, which are further scaled to reproduce the experimental exoergicity of the reaction. In addition, the spin-orbit, Coriolis, and electrostatic couplings between the three quasidiabatic F+H2 electronic states are included. The calculated integral cross sections are compared with the results of molecular beam experiments. At low collision energies, a significant fraction of the reaction is due to Born-Oppenheimer forbidden, but energetically allowed reaction of F in its excited (2P 1/2) spin-orbit state. As the collision energy increases, the Born-Oppenheimer allowed reaction of F in its ground (2P 3/2) spin-orbit state rapidly dominates. Overall, the calculations agree reasonably well with the experiment, although there remains some disagreement with respect to the degree of rotational excitation of the HF(v'=3) products as well as with the energy dependence of the reactive cross sections at the lowest collision energies.     

两种烷基碘化物分子理论研究及其发射谱测量

利用密度泛函理论(DFT)的B3LYP方法, 对烷基碘化物分子C2H2F3I和n-C3H4F3I的C—I解离势能曲线进行了理论计算, 并采用B3LYP方法和MPn(n=2, 3, 4)方法精确计算了C—I键解离能. 解离能计算进行了零点振动能(ZPVE)校正, 并运用完全均衡校正法对基函数重叠误差(BSSE)进行校正. 利用微波放电激励方法, 对C2H2F3I和n-C3H4F3I的发射谱进行观测. 实验结果表明, 通过微波放电激励这两种分子, 均可产生1315 nm发射谱, 说明利用微波放电可使C2H2F3I和n-C3H4F3I分子的C—I键解离, 从而产生碘原子.     

Ab initio potential energy surface and rovibrational spectrum of Ar-HCCCN

We report an ab initio intermolecular potential energy surface of the Ar-HCCCN complex using a supermolecular method. The calculations were performed using the fourth-order M?ller-Plesset theory with the full counterpoise correction for the basis set superposition error and a large basis set including bond functions. The complex was found to have a planar T-shaped structure minimum and a linear minimum with the Ar atom facing the H atom. The T-shaped minimum is the global minimum with the well depth of 236.81 cm(-1). A potential barrier separating the two minima is located at R=5.57 A and theta=20.39 degrees with the height of 151.59 cm(-1). The two-dimensional discrete variable representation was employed to calculate the rovibrational energy levels for Ar-HCCCN. The rovibrational spectra including intensities for the ground state and the first excited intermolecular vibrational state are also presented. The results show that the spectra are mostly b-type (Delta K(a)=+/-1) transitions with weak a-type (Delta K(a)=0) transitions in structure, which are in good agreement with the recent experimental results [A. Huckauf, W. Jager, P. Botschwina, and R. Oswald, J. Chem. Phys. 119, 7749 (2003)].     

A new ab initio intermolecular potential energy surface and predicted rotational spectra of the Ar-H2S complex

We report a reliable three-dimensional ab initio intermolecular potential energy surface for the Ar-H(2)S complex with H(2)S monomer fixed at its experimental average structure. The potential energies were evaluated using the supermolecular approach at the coupled-cluster level with a large basis set including bond functions. The full counterpoise procedure was used to correct the basis set superposition error. The potential has a planar T-shaped global minimum with a well depth of 177.48 cm(-1) at the intermolecular distance of 3.72 ?. An additional planar local minimum is also found and is separated from the global minimum with an energy barrier with a height of 47.46 cm(-1). The combined radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm were employed to calculate the rovibrational energy levels for three isotopic species of Ar-H(2)S complexes (Ar-H(2)(32)S, Ar-H(2)(33)S, and Ar-H(2)(34)S). The rotational transition frequencies and structural parameters for the three isotopomers were also determined for the ground and the first excited states, which are all in good agreement with the available experimental values.     

Complete Cl calculations on the ground state of HeH

Complete Cl calculations on the van der Waals molecule HeH with a large Gaussian basis set give the depth of the potential well as c = 0.50 meV and a minimum at R_m = 3.64 Å. An analytical function has been fitted to the ab initio points and to the best estimates of the dispersion energy coefficients. One further parameter in the potential has been chosen to reproduce the HeH scattering cross section.