钒硫团簇V2S2+、V3S4+的结构和稳定性

用ab initio分子轨道方法(RHF,UHF)和密度泛函(DFT)方法研究了团簇V2S2+、V3S4+的各种可能的几何构型和电子结构,所得理论计算能较好地解释有关实验结果.     

钴硫团簇ConSn+-1(n=2,3)的结构和稳定性

用ab initio分子轨道方法(RHF,UHF)和密度泛函(DFT)方法研究了团簇Co2S+,Co3S2+的各种可能的几何构型和电子结构,并计算了相应的较稳定构型的振动光谱,发现Co2S+和Co3S2+团簇最稳定结构均具有C,对称性.对团簇的成键作用机理进行了理论分析.     

巴豆醛在Au(111)面上的吸附及选择性加氢机理研究

采用密度泛函理论计算了巴豆醛4种构型的稳定性,并选取最优构型进一步研究了其Au(111)面上的吸附及选择性加氢机理.计算结果表明,具有E-(s)-trans构型的巴豆醛稳定性最高.当巴豆醛通过C O吸附于Au(111)面的顶位时,该构型吸附能最大,吸附模型最稳定;巴豆醛向Au(111)表面转移电子0.045e,且其p轨道与金属表面的d轨道发生较强相互作用,使得巴豆醛的键级减弱.此外,通过分析各基元反应的活化能、反应热以及构型变化可知,巴豆醛在Au(111)面上按照2,1-加成机理(部分加氢机理)生成巴豆醇的可能性最大,且降低温度有利于反应转化率的提高.     

聚磷链和聚氮链的自洽场晶体轨道研究

利用自治场全略微分重叠晶体轨道方法(SCFCNDO/2-CO)对聚磷链和聚氮链的各种可能构型的稳定性、能带结构和电子特性进行了研究.结果表明,本征聚磷链为半导体,而本征聚氮链为绝缘体.     

过渡金属卡宾正离子的理论研究

以从头算研究了第一过渡系金属卡宾正离子MCH 2 的构型和成键特征(HF/LANL2DZ) .所有的MCH 2 均为共平面构型 ( yz平面内 ) .闭壳层构型中 ,C ,M间为一个完整的双键 ,而在开壳层构型中σ和π轨道之一为单电子占有 ,形成一个不完整的双键 .π轨道主要由卡宾碳的 2 px 与M的 4px 和 3dxz侧面交盖而成 .从Sc到Cu ,CM键解离能呈周期性变化 .多数计算的CM键解离能与实验值接近 .     

六氢吡啶和氨形成的氢键团簇C5H10NH(NH3)n(n=1～3)结构的从头算研究

在RHF/6-31G(d)水平下,对C5H10NH(NH3)n(n=1～3)氢键团簇的平衡构型进行了从头算研究,优化得到各种可能的平衡构型.C5H10NH(NH3)为线型氢键结构,而C5H10NH(NH3)2为三元环结构,C5H10NH(NH3)3为四元环结构.在MP2/6-31G(d)//B3LYP/6-31G(d)水平下,对最稳定构型C5H10NH(NH3)n(Ⅰ)(n=1～3)的分子轨道进行布居分析,并且对相应的占据轨道进行指认.C5H10NH(NH3)n(Ⅰ)(n=1～3)垂直电离势的计算结果表明,形成氢键团簇后,分子的垂直电离势降低.     

分子团簇的量子化学研究

采用Hartree-Fock方法、密度泛函(DFT)方法(BLYP、B3LYP)和MP2方法对Se4分子团簇的各种可能构型进行了结构优化和频率分析, 结果表明有5种构型是势能面上的稳定驻点, 同时对上述4种量子化学方法计算结果的差异进行了分析。并对这5种构型的结构稳定性、几何构型、前线分子轨道、Mulliken布局分析和偶极矩进行了分析, 根据分析结果对Se4分子的某些物理和化学性质进行了预测。     

5d过渡金属原子中心镶嵌Ag团簇M@Ag12(M＝Hf～Hg) Ih和Oh构型的密度泛函理论研究

采用相对论密度泛函理论方法对Ih和Oh构型M@Ag12 (M＝Hf～Hg)的几何和电子结构进行了系统的研究. 研究表明, 原子半径之和与团簇的电子结构共同决定了M—Ag键长的大小. M@Ag12的成键能来自中心原子的嵌入能和Ag12笼子的形变能. 最高占据轨道为成键轨道的团簇比反键轨道的团簇的稳定性强. 我们发现在此系列中, Ih构型不一定总比Oh构型稳定. Hf@Ag12, Ir@Ag12, Au@Ag12和Hg@Ag12的Oh构型比Ih构型稳定.     

Pd/Au(100)表面上乙烯气相氧化法合成乙酸乙烯酯催化活性的密度泛函理论研究

采用密度泛函理论方法系统地研究了Pd/Au(100)表面上乙烯气相氧化法合成乙酸乙烯酯的催化活性.对关键反应物种在该表面的吸附、共吸附性质及耦合基元反应进行了计算和讨论.乙烯在Pd/Au(100)表面上存在π-,2σ-两种稳定吸附构型,为弱化学吸附;乙酸根物种存在Pd-Au与Pd-Pd两种二位啮合(bi-dentate)构型,为强化学吸附.Pd/Au(100)表面的吸附作用使两个关键反应物种分子轨道能量靠近.共吸附构型中最高占据和最低未占据分子轨道的能级差(HOMO-LUMO-gap)随表面相邻Pd原子数目的增多而增大,表明由HOMO向LUMO分子轨道发生电子转移的能力变弱.耦合基元反应过渡态能垒的分析结果与HOMO-LUMO-gap定性分析结果一致,说明连续相邻的表面Pd原子不利于反应的进行.     

Zn(Ⅱ)/γ-MnOOH体系化学吸附的密度泛函理论研究

采用密度泛函B3LYP方法对Zn(Ⅱ)在水锰矿(MnOOH)2(H2O)6簇模型表面的水合、一级和二级水解三类共11种吸附构型进行了理论研究. 计算结果表明, 水合吸附构型的稳定性顺序为DC(双角)>SE-B(单边-B)>SE-A(单边-A)>DE(双边), 水解吸附构型的稳定性顺序为DC>SE-A>SE-B>DE, 均符合鲍林第三规则; 热化学分析结果说明, 其吸附和水解是相互制约的两个过程, 这一结论通过前线轨道理论分析得到了证明; 自然布居分析结果表明, 吸附过程中电子由簇模型向吸附质迁移; 结合电子供体-受体相互作用和前线轨道组成分析了吸附产物的稳定性.     

限制性自洽场开壳层CNDO/2方法

本文采用限制性自洽场CNDO/2方案,在IBM-PC/XT微机上实现了RHF的CNDO/2计算程序。计算了若干开壳层的小分子和含过渡金属的配合物, 得到体系总能量、电荷、键序、结合能, 与UHF的CNDO/2方法计算结果完全符合, 并且图象清晰·RHF的CNDO/2的方法的实现为半经验方法计算开壳层体系电子光谱跃迁强度, 磁超精细结构常数以及酉群的组态相互作用提供了一个好的波函数。     

Approximate calculation of the correlation energy for the closed and open shells

A formula is derived for the approximate calculation of the correlation energy of both open and closed shell systems. The formula integrates a functional of the one- and two-electron density matrices, obtained from a wavefunction built up by one or several Slater determinants.Some test calculations on the ground state of diatomic molecules at several internuclear distances and on many excited states of atoms and molecules show the goodness of this method.     

Radical ions and radicals in electron-irradiated acrylates and N-isopropylacrylamide: a quantum chemical study

The semiempirical quantum chemical methods MNDO, AM1 and PM3 were used to investigate the performance of the single excited configuration interaction (SCI) approximation for calculating low energy excitation energies of open-shell systems. Systematic calculations were done for eight radicals formed by reactions of H√, OH√ and e⁻_aq with various acrylates and N-isopropylacrylamide. The calculated electronic spectra show a reasonable correlation with experimental data for both neutral radicals and radical ions. The AM1 as well as the PM3 formalism can be successfully applied to calculate the low energy excited states of these types of open shell systems. The best correlation between experimental and calculated excitation energies was obtained using the PM3 method (correlation coefficient 0.96, overall average error 0.16 eV).     

Application of the method of increments to the adsorption of CO on the CeO2(110) surface

We have combined an embedded-cluster model with an extension of the method of increments to treat the adsorption of molecules on a surface. In this way we are able to investigate the physisorption of CO on CeO(2)(110) at the MP2, MP4(SDTQ), and CCSD(T) levels with only moderate computational costs. We find that, at the CCSD(T) level, 25% of the adsorption energy originates from electron correlation. The interactions of the CO molecule with its five nearest cerium and oxygen neighbors in the surface layer make the largest contributions to the electron correlation. Approximately 97% of the adsorption-induced electron correlation energy part of the adsorption energy is recovered by the method of increments (in our chosen expansion), at the MP2 level.     

Finite temperature path integral Monte Carlo simulations of structural and dynamical properties of Ar(N)-CO(2) clusters

We report finite temperature quantum mechanical simulations of structural and dynamical properties of Ar(N)-CO(2) clusters using a path integral Monte Carlo algorithm. The simulations are based on a newly developed analytical Ar-CO(2) interaction potential obtained by fitting ab initio results to an anisotropic two-dimensional Morse∕Long-range function. The calculated distributions of argon atoms around the CO(2) molecule in Ar(N)-CO(2) clusters with different sizes are consistent to the previous studies of the configurations of the clusters. A first-order perturbation theory is used to quantitatively predict the CO(2) vibrational frequency shift in different clusters. The first-solvation shell is completed at N = 17. Interestingly, our simulations for larger Ar(N)-CO(2) clusters showed several different structures of the argon shell around the doped CO(2) molecule. The observed two distinct peaks (2338.8 and 2344.5 cm(-1)) in the υ(3) band of CO(2) may be due to the different arrangements of argon atoms around the dopant molecule.     

Density embedded VB/MM: a hybrid ab initio VB/MM with electrostatic embedding

A hybrid QM/MM method that combines ab initio valence-bond (VB) with molecular mechanics (MM) is presented. The method utilizes the ab initio VB approach to describe the reactive fragments and MM to describe the environment thus allows VB calculations of reactions in large biological systems. The method, termed density embedded VB/MM (DE-VB/MM), is an extension of the recently developed VB/MM method. It involves calculation of the electrostatic interaction between the reactive fragments and their environment using the electrostatic embedding scheme. Namely, the electrostatic interactions are represented as one-electron integrals in the ab initio VB Hamiltonian, hence taking into account the wave function polarization of the reactive fragments due to the environment. Moreover, the assumptions that were utilized in an earlier version of the method, VB/MM, to formulate the electrostatic interactions effect on the off-diagonal matrix elements are no longer required in the DE-VB/MM methodology. Using DE-VB/MM, one can calculate, in addition to the adiabatic ground state reaction profile, the energy of the diabatic VB configurations as well as the VB state correlation diagram for the reaction. The abilities of the method are exemplified on the identity SN2 reaction of a chloride anion with methyl chloride in aqueous solution. Both the VB configurations diagram and the state correlation diagram are presented. The results are shown to be in very good agreement with both experimental and other computational data, suggesting that DE-VB/MM is a proper method for application to different reactivity problems in biological systems.     

导电高聚物聚吡啶的电子能带及其结构研究

聚吡啶(简称PPy)易于进行n-型掺杂并使其电导率大大提高,可用于制作高聚物电池的负极,本文将PPy视为准一维体系,采用EHMO/CO方法计算了新合成的导电高分子材料--聚吡啶4种可能构型的电子能带。     

Confinement effects on the electronic structure of M‐shell atoms: A study with explicitly correlated wave functions

The ground and some excited states of Na and Mg atoms confined at the center of a spherical box with impenetrable walls are studied. Variational wave functions including dynamic correlations and configuration mixing have been obtained. Level crossings induced by confinement have been analyzed in terms of the energy of the occupied orbitals of the M shell and the weight of the different configurations. Confinement effects on the correlation energy have been studied. The parameterized optimized effective potential and the variational Monte Carlo methods have been employed. A cut off‐factor has been included to account for the hard wall confinement.     

Electronic structure of the ground state of the benzyl radical

Results from the -electron approximation are given for the total energy, spin-density distribution, and electron density, which have been derived by configuration interaction via self-consistent orbitals for closed and open shells and with allowance for all singly excited configurations and some doubly excited ones. Some singly excited configurations do not mix with the ground-state configuration in the first order of perturbation theory but make a contribution to the latter greater than do some of the configurations that do mix. Incorporation of all singly excited configurations results in a lower ground-state energy if orbitals for a closed shell are used instead of those for an open one. Calculations via closed-shell orbitals lead to an inhomogeneous electron-density distribution, which is gradually smoothed out as the set of configurations is expanded. The spin-density distribution is very much dependent on the number of configurations used and on the orbitals employed in them.     

Vibrational quasi-degenerate perturbation theory: applications to fermi resonance in CO2, H2CO, and C6H6

A quasi-degenerate perturbation method with vibrational self-consistent field (VSCF) reference wavefunction is developed. It simultaneously accounts for strong anharmonic mode-mode coupling among a few states (static correlation) by a configuration interaction theory and for weak coupling with a vast number of the other states (dynamic correlation) by a perturbation theory. A general formula is derived based on the van Vleck perturbation theory. An algorithm that selects a compact set of the most important VSCF configurations which contribute to the static correlation is proposed and a scheme to limit the number of configurations considered for dynamic correlation is also implemented. This method reproduces the vibrational frequencies of CO2 and H2CO that are subject to the strongest anharmonic mode-mode coupling within 10 cm(-1) of vibrational configuration interaction results in a computational expense reduced by a factor of one to two orders of magnitude. The method also reproduces the infrared absorption of C6H6 in the CH stretching (nu12) frequency region, in which combination tones nu13nu16 and nu2nu13nu18 appear on account of an intensity borrowing from nu12via the anharmonic coupling.