甲硅硫醛(H2SiS)脱氢反应的反应路径解析

本文用内禀反应坐标(IRC)方法讨论了甲硅硫醛分子的脱氢反应机理. 在RHF/4-31G基组上对此反应做了量子化学从头计算和反应路径解析, 得到H_2SiS的平衡几何、过渡态结构、反应势能曲线、活化能, 反应热以及沿反应坐标一些物理量的变化, 并对平衡几何和过渡态做了振动分析. 同时, 计算了反应的频率因子A和在500 K时的活化熵△S≠。     

一种研究Aa型缩聚反应体系的新方法

应用统计力学基本原理, 从两种不同角度构造了Aa型缩聚反应的正则配分函数, 得到了体系的平衡自由能以及质量作用定律的解析表达式, 提出了获得数量分布函数的两种新方法. 进一步基于数量分布函数的不变性, 给出临界点后溶胶相和凝胶相的平衡自由能, 证明溶胶-凝胶相变是一类几何相变, 而非热力学相变.     

去氢抗坏血酸分子振动光谱的理论研究

采用RHF, MP2, DFT(B3LYP)方法, 以6-311++G**为基组研究了去氢抗坏血酸分子(DHA)的平衡几何构型和振动光谱. 计算结果表明, 采用RHF, B3LYP以及MP2 方法优化得到的几何结构以及频率值是一致的. 采用B3LYP/6-311++G**计算了DHA分子平衡构型下的谐振动力场﹑振动频率和振动强度. 使用Wilson的GF矩阵方法对DHA分子进行了简正坐标分析, 依据所得的势能分布对DHA分子的振动基频进行了合理的理论归属.     

几种过渡态结构的有效优化方法

通过双桥反应机理、电环合反应和催化反应三个不同类型的过渡态优化，说明当标准方法难以给出结果时，对物理问题本身的分析有助于给出过渡态优化的线索．第一个例子根据化学问题给出限制条件，通过平衡几何构型优化方法优化得到过渡态；第二个例子是在使用标准过渡态优化方法失败后，根据物理问题从反应途径上用平衡几何构型优化方法选择过渡态优化的初始结构；第三个例子通过Gaussian 98程序中的标准方法QST2直接得到过渡态．     

线型碳链PC2nP的结构和电子光谱的密度泛函理论研究

应用密度泛函理论,在B3LYP/6-31G**和B3LYP/6-311G**水平上优化得到了线型簇合物PC2nP(n=1-10)的基态平衡几何构型,计算了它们的谐振动频率.在基态平衡构型下,利用含时密度泛函理论,计算得到了簇合物PC2nP(n=1-10)的垂直激发能和相应的振子强度,导出了激发能与体系大小n的解析关系式.     

PuN和PuN_2基态分子的结构与势能函数

用相对论有效原子实势和密度泛函理论方法对PuN和PuN_2分子的结构进行优化 ，得到了其平衡几何构型和谐振频率。采用最小二乘法拟合出PuN基态分子的 Murrell-Sorbie解析势能函数，在此基础上推导出光谱数据和力常数，并用多体展 式理论导出PuN_2基态分子的解析势能函数，正确地反映了其平衡构型特性。     

类氮烯HNLiF构型和异构化反应理论研究

本文在量子化学从头算水平上, 用RHF/3-21G方法和梯度解析技术研究了类氮烯HNLiF势能面的主要特征, 得到三种平衡几何构型和两个异构化反应过渡态构型。平衡构型的能量按三元环构型、σ构型和p构型的顺序递增。三元环构型为类氮烯的主要存在形式。文中分析了各构型特点并给出其电荷分布和前线轨道。为用类氮烯合成含氮化合物提供了理论依据。     

2|4-二氯-5-硝基嘧啶甲胺化的ab initio研究

2，4-二氯-5-硝基嘧啶的甲胺化反应是制备鸟嘌呤衍生物中间体的重要反应[1]，实验发现该反应主要有三种产物：究竟哪种产物占优势？主要由反应物（Ⅰ）和甲胺分子的电子结构性质决定，本文对反应物（Ⅰ）和甲胺的电子结构性质进行了abinitio研究．采用RHF能量梯度法，在DZ基组水平上对反应物（Ⅰ）和甲胺分子进行全分子几何优化，梯度模收敛指标控制为0刀003·对得到的平衡几何进行市居数分析和静电势研究．计算采用Tulbomole程序［到在SGI图形工作站上完成．反应物（I）分子的平衡几何如图1所示．从优化后的结构可知，硝基和南吠环不在…     

线性BC2nB (n＝1～12)的结构特征和电子光谱的理论研究

应用密度泛函理论, 在B3LYP/6-31G^*水平上优化得到了线性簇合物BC_2nB (n＝1～12, D_(h)的平衡几何构型, 并计算了它们的谐振动频率. 在优化平衡几何构型下, 通过TD-B3LYP/cc-pvDZ和TD-B3LYP/cc-pvTZ计算, 分别得到了n＝1～12和n＝1～7的电子跃迁的垂直激发能和对应的振子强度. 在B3LYP/6-311＋G^*水平上计算得到了簇合物BC_2nB (n＝1～12, D_(h)的电离能. 基于计算结果, 导出了BC_2nB体系电子跃迁能以及第一电离能与体系大小n的解析表达式.     

吡啶甲酸分子平衡构型的ab initio理论研究

本文用能量梯度法TEXAS从头计算程序,选取4-21G(,N原子含极化d轨道)基组,对α-,β-吡啶甲酸分子的平衡几何构型进行了全优化计算,二套基组的理论优化表明,三个吡啶甲酸分子都具有平面的平衡构型,其计算键长经4-21G 基组的标准经验校正值校正后,所得的理论预测平衡几何构型与X射线单晶衍射实验结果有很好的一致性.对部分键长以及羧基与吡啶华平面的二面角中出现的差异进行了讨论.     

Ab initio study of the intermolecular potential energy surface in the ion-induced-dipole hydrogen-bonded O2(-)(X2Πg)-H2(X1Σg(+)) complex

This work presents the first investigation on the intermolecular potential energy surface of the ground electronic state of the O2(-)(2Πg)-H2(1Σg(+)) complex. High level correlated ab initio calculations were carried out using the Hartree-Fock spin-unrestricted coupled cluster singles and doubles including perturbative triples correction [RHF-UCCSD(T)]/aug-cc-pVXZ levels of calculations, where XZ = DZ, TZ, QZ, and 5Z. Results of full geometry optimization and the intermolecular potential energy surface (IPES) calculations show four equivalent minimum energy structures of L-shaped geometry with Cs symmetry at equilibrium along the 2A″ surface of the complex. For these equilibrium minimum energy structures, the most accurate value for the dissociation energy (De) was calculated as 1407.7 cm(-1), which was obtained by extrapolating the counterpoise (CP) corrected De values to the complete basis set (CBS) limit. This global minimum energy structure is stabilized by an ion-induced-dipole hydrogen bond. Detailed investigations of the IPES show that the collinear structure is unstable, while the C2v geometries present saddle points along the 2A″ surface. The barrier height between the two equivalent structures that differs in whether the hydrogen-bonded hydrogen atom is above or below the axis that connects centers of masses of the H2 and O2(-) moieties within the complex was calculated as 70 cm(-1). This suggests that the complex exhibits large amplitude motion. The barrier height to rotation of the H2 moiety by 180° within the complex is 1020 cm(-1). Anharmonic oscillator calculations predicted a strong H-H stretch fundamental transition at 3807 cm(-1). Results of the current work are expected to stimulate further theoretical and experimental investigations on the nature of intermolecular interactions in complexes that contain the superoxide radical and various closed-shell molecules that model atmospheric and biological molecules. These studies are fundamental to understanding the role of the O2(-) anion in chemistry in the atmosphere and in biological systems.     

PH~3...H~2O体系分子间相互作用的从头计算MO研究

在MP2/6-311++G(3d,3p)水平,对PH~3...H~2O体系可能存在的氢键复合物进行了全自由度能量梯度优化,发现PH~3...H~2O体系存在三个能量极小结构A,B和C。其中结构A和B以H~2O作为质子授体,结构C以PH~3作为质子授体,结构A较结构B和C分别稳定6.52kJ/mol和8.18kJ/mol。结构A具有C~s对称性,其结构中P原子和O原子间距离为354.78nm,键角OHP为171.35ⅲ,属于接近于直线的传统型氢键结构。进一步在高级电子相关校正的MP4SDTQ下,用6-311++G(3df,3pd)基加上键函数{3s3p2d1f},通过BSSE校正,精确计算了结构A的结合能为-10.84kJ/mol。     

Photodissociation spectroscopy of Zn+(H2O) and Zn+(D2O)

We report on a study of the photodissociation spectroscopy of weakly bound Zn+(H2O) and Zn+(D2O) complexes. The work is supported by ab initio electronic structure calculations of the ground and low-lying excited energy surfaces. We assign two molecular absorption bands in the near UV correlating to Zn+ (4s-4p)-based transitions, and identify vibrational progressions associated with both intermolecular and intramolecular vibrational modes of the cluster. Partially resolved rotational structure is consistent with a C(2V) equilibrium complex geometry. Experimental spectroscopic constants are in very good agreement with ab initio theoretical predictions. Results are compared with previous work on main group and transition metal ion-H2O clusters.     

二氧化钚分子的多体展式势能函数

从导出基态PuO2分子的电子状态X5Σ g正确地判断其离解极限出发,采用MP2方法,应用相对论有效原子实模型(RECP)优化出PuO2(X5Σ g)分子稳定构型为线性OPuO(D∞h),其平衡核间距Re=0.18004nm.同时也计算出振动频率,并优化出存在亚稳态的Pu-O-O(C∞v)构型.使用多体项展式理论方法,导出了基态PuO2分子的分析势能函数.该势能表面准确地再现了O-Pu-O(D∞h)平衡结构和亚稳态的Pu-O-O(C∞v)构型.然后根据势能函数等值图讨论了O(3Pg) PuO反应的势能面静态特征.     

DFT Studies on Thermal Stabilities,Electronic Structures,and ~（13）C Chemical Shifts of C_（24）O_2 Based on Fullerene C_（24）（D_6）

Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 (D6) and C24O have been performed using density functional theory (DFT) method. The geometric and electronic structures as well as the relative energies and thermal stabilities of various C24O2 isomers at the ground state have been calculated at the B3LYP/6-31G(d) level of theory. And the 1,4,2,5-C24O2 isomer was found to be the most stable geometry where two oxygen atoms were added to the longest carbon-carbon bonds in the same pentagon from a thermodynamic point of view. Based on the optimized neutral geometries, the vertical ionization potential and vertical electron affinity have been obtained. Meanwhile, the vibrational frequencies, IR spectrum, and 13C chemical shifts of various C24O2 isomers have been calculated and analyzed.     

Theoretical study of the electronic nonadiabatic transitions in the photoelectron spectroscopy of F2O

The photoelectron spectrum of F2O pertaining to ionizations to the ground (X2B1) and low-lying excited electronic states (A2B2, B2A1, and C2A2) of F2O+ is investigated theoretically. The near equilibrium potential energy surfaces of the ground electronic state (X2B1) of F2O and the mentioned ground and excited electronic states of F2O+ reported by Wang et al. ( J. Chem. Phys. 2001, 114, 10682) for the C2v configuration are extended for the Cs geometry assuming a harmonic vibration along the asymmetric stretching mode. The vibronic interactions between the A2B2 and B2A1 electronic states of F2O+ are treated within a linear coupling approach, and the strength of the vibronic coupling parameter is calculated by an ab initio method. The nuclear dynamics is simulated by both time-independent quantum mechanical and time-dependent wave packet approaches. Although the first photoelectron band exhibits resolved vibrational progression along the symmetric stretching mode, the second one is highly overlapping. The latter is attributed to the nonadiabatic interactions among the energetically close A2B2, B2A1, and C2A2 electronic states of F2O+. The theoretical findings are in good accord with the available experimental results.     

The case of the weak N-X bond: Ab initio, semi-experimental, and experimental equilibrium structures of XNO (X = H, F, Cl, OH) and FNO2

The equilibrium structures of FNO, ClNO, HONO, and FNO2 have been determined using three different, somewhat complementary methods: a completely experimental, a semi-experimental (where the equilibrium rotational constants are derived from the experimental effective ground-state rotational constants and an ab initio cubic force field), and an ab initio, where geometry optimizations are usually performed at the coupled cluster level of nonrelativistic electronic structure theory using small to very large Gaussian basis sets. For the sake of comparison, the equilibrium structures of HNO and N2O have also been redetermined, confirming and extending earlier results. The semi-experimental method gives structural parameters in good agreement with the reliable experimental results for each compound investigated. Because of inadequate treatment of electron correlation, the single-reference CCSD(T) method gives N-X (X[double bond]F, Cl, OH) bonds that are too strong and associate bond lengths that are significantly too short. The discrepancy increases with increase in the size of the basis set. A much more elaborate treatment of electron correlation at the CCSDTQ level solves this problem and results in increased bond lengths, correctly representing the weakness of the N-X bond in these XNO and XNO2 species. The equilibrium structures determined are accurate to better than 0.001 A and 0.1 degrees .     

Searching blue-shifted O–H···Y hydrogen bond in CH<Subscript>3</Subscript>OH complexes with CF<Subscript>4</Subscript>, C<Subscript>2</Subscript>F<Subscript>2</Subscript>, OC,Ne, and He: a theoretical study

The hydrogen-bonded structures of the CH₃OH complexes with CF₄, C₂F₂, OC, Ne, and He are designated as the starting points for geometry optimizations without and with counterpoise (CP) correction at MP2 level of theory with the basis sets 6-31+G*, 6-31++G**, and 6-311++G**, respectively. Tight convergence criteria are applied throughout all geometry optimizations in order to reduce the computational errors. According to the optimizations without CP correction, a blue-shifted O–H···Y (where Y = F, O, Ne, or He) hydrogen bond exists in all these five complexes. The magnitudes of blue shifts of ν(O–H) of the former four complexes with respect to that of CH₃OH are reduced greatly when the polarization and diffuse functions of the hydrogen atoms are added (results from 6-31+G* versus those from 6-31++G**). However, for the complexes CH₃OH–CF₄ and CH₃OH–C₂F₂, our optimizations using the CP corrections did not find the hydrogen-bonded structure to be a stationary point. The energy minimum of both the complexes corresponds to a non-hydrogen-bonded structure.     

A diffusion quantum Monte Carlo study of geometries and harmonic frequencies of molecules

This article describes an approach in determination of equilibrium geometries and harmonic frequencies of molecules by the Ornstein-Uhlenbeck diffusion quantum Monte Carlo method based on the floating spherical Gaussians. In conjunction with a projected and renormalized Hellmann-Feynman gradient and an electronic energy at variational Monte Carlo and diffusion quantum Monte Carlo, respectively, the quasi-Newton algorithm implemented with the Broyden-Fletcher-Goldfarb-Shanno updated Hessian was used to find the optimized molecular geometry. We applied this approach to N2 and H2O molecules. The geometry and harmonic frequencies calculated were consistent with some sophisticated ab initio calculated values within reasonable statistical uncertainty.     

Ionic reactions in He nanodroplets: the [LiHHe]+ complex and its possible energy pathways into products from ab initio calculations

Ab initio calculations at the multiconfiguration self-consistent field level followed by a multireference configuration interaction were carried out along the two possible collinear approaches of the [LiHHe]+ system, while a three-dimensional calculation of the structures of that complex with LiH+ kept at its equilibrium geometry was also completed at the same level of accuracy. The interaction forces of the lowest two electronic states indicate possible reactive behavior, with the first excited potential-energy surface clearly showing a barrierless path to HeH+ product formation. The details of the reactive pathways and their possible bearing on reaction processes, which could occur at the low temperature of a He nanodroplet holding LiH+ as an impurity, are analyzed and discussed.