电场作用下分子导线的理论研究

摘要利用从头计算法分别在HF/6-31G, HF/6-31G*, HF/6-31G**, HF/6-31+G, HF/6-31++G, HF/6-31+G*, HF/6-31+G**, HF/D95+*, B3LYP/6-31G*和B3LYP/6-31+G*水平上计算了5个单体的聚乙炔分子导线, 从几何构型、 SCF能量和分子轨道能级三个方面讨论了外电场对分子导线的影响, 给出了聚乙炔分子导线性质与外电场变化的定量关系.     

NH_2(~2B_1)与CH_4反应机理的理论研究

在密度泛函理论 B3LYP/6 -31 1 G*水平下 ,研究了 NH2 与 CH4的反应机理 .通过振动频率和内禀反应坐标 ( IRC)分析 ,对反应过渡态进行了确认 .在 QCISD( T) /6 -31 1 G*水平下进行了单点能计算 ,并进行了零点能校正 ,结果表明 ,反应 NH2 + CH4NH3 + CH3 是主要的反应通道 .     

两种8-羟基喹啉锌配合物电子结构和光谱性质的理论研究

采用密度泛函理论在PBE0/6-31+G(d)-LANL2DZ水平下优化了两种8-羟基喹啉锌配合物的基态几何构型,并在相同水平下进行了频率分析以确认稳定点的性质.根据基态优化的构型,在TD-PBE0/6-31+G(d)-LANL2DZ水平下,采用极化连续介质模型(PCM)计算了甲醇溶剂中配合物的电子结构和电子吸收光谱.计算结果表明,配合物B中8-羟基喹啉2号位取代基蒽较大的π共轭作用使其具有较小的HOMO-LUMO能级差,从而使配合物B的最大吸收波长发生了红移现象.     

TMS的NMR量子化学计算

分别用HF/4-31G(Si=6-21G)、B3LYP/6-31G(D)、B3LYP/6-31G、HF/6-31G、MP2/6-31G(D)对TMS进行了结构优化,在此基础上,用Hartree-Fock、B3LYP理论水平下,分别用不同的基组6-31G、6-31++G(D,P)、6-311+G(2D,P)、6-311++G(D,P)进行NMR的计算;在MP2理论水平上,用STO-3G、3-21G、4-31G、6-31G、6-31G(D)、6-31++G(D,P)等基组进行NMR的计算.并用GAUSSION98程序所给出的四种计算NMR的方法:GIAO、IGAIM、CSGT、SINGLE GAUGE ORIGIN,分别在上述基础上进行了TMS的屏蔽值的计算.研究结果表明,就理论水平而言,DFT(B3LYP)比HF计算结果要好,而且基组越大,计算精度越高,但有一饱和基组存在.就计算方法而言,用GIAO有利于计算精度的提高.计算结果与实验值基本上吻合.     

镍和钯两种金属配合物电子结构和光谱性质的理论研究

采用密度泛函理论(DFT),在PBE0/6-31+G(d)-LANL2DZ水平下优化了Ni和Pd两种金属配合物A和B的基态几何构型,并在相同水平下进行了频率分析以确认都是实频.利用含时密度泛函理论(TD-DFT)和极化连续介质模型(PCM),在TD-PBE0/6-31+G(d)-LANL2DZ水平下,计算了配合物A和B在二氯甲烷溶剂中的电子结构和吸收光谱.计算结果表明,与中心配位原子Pd相比,Ni较强的配位作用使配合物A具有较小的HOMO-LUMO能级差,从而导致配合物A的最大吸收波长发生红移.     

量子化学研究水对Adenine-Thymine碱基对构型的影响

利用Hartree-Fock方法, 选取6-31G*基组对Adenine-Thymine-Water氢键复合物可能存在的构型进行了优化, 然后用DFT PBE方法, 选取6-311＋＋G(3d, 3p)基组对复合物的结合能进行计算, 结果表明水与DNA中配对碱基的相互作用, 不会显著影响碱基对的稳定性, 水的存在使得碱基对的扭转构型更接近真实DNA中碱基对的螺旋状结构.     

大气中OH引发的有机磷农药MTMPDA降解机理的研究

采用量子化学方法在ωB97XD/6-311++G(3df,2pd)//ωB97XD/6-31+G(d,p)和M062X/6-311++G(3df,2pd)//M062X/6-31+G(d,p)水平下对大气中MTMPDA在OH自由基引发下的反应机理及其产物的后继反应进行理论研究.结果表明MTMPDA+OH反应主要通过OH抽提与N原子相连的—CH3上的H原子、以及抽提与O原子相连的—CH3上的H原子的方式进行.此外,抽提与N原子相连的—CH3上的H原子生成的产物与大气中的O2和NO发生进一步反应并没有导致MTMPDA毒性明显地降低;而抽提与O原子相连的—CH3上的H原子的产物发生一系列后继反应可以降低MTMPDA的毒性.     

H-ZSM-5催化环己酮肟制ε-己内酰胺反应机理的ONIOM研究

采用ONIOM和DFT方法研究了H-ZSM-5分子筛催化环己酮肟制ε-己内酰胺的贝克曼重排反应机理.所有的构型优化使用ONIOM(B3LYP/6-31+G(d):PM3)方法进行,并在此基础上对得到的最优构型应用多种密度泛度方法,如B3LYP/6-31+G(d),PBE/6-31+G(d),M062X/6-31+G(d)和ωB97XD/6-31+G(d)进行完整46T簇模型的单点能计算.B3LYP,PBE和M062X泛函使用dftd3程序计算了额外色散校正,以考虑分子筛内部的弱相互作用.计算结果显示,经色散校正的DFT方法的计算精度被大大提高,达到一个与MP2方法相媲美的精度.反应的决速步是由第一步1,2-H转移和重排步共同决定,内部反应能垒为44.5 kcal/mol.反应速率常数表明,在293~393 K时,在H-ZSM-5上贝克曼重排反应进行得相当缓慢;当温度达到423 K时,正逆反应速率相当,反应开始发生;当达到623 K时,反应速率常数为130 1/s.     

6-甲基-4-羟基嘧啶单体及二聚体激发态质子转移异构化反应及光谱的理论研究

采用ab initio HF理论的组态相关CIS方法和连续溶剂模型PCM, 分别在6-311+G*和6-31G水平上研究了6-甲基-4-羟基嘧啶单体及二聚体激发态质子转移的异构化反应; 对其反应势能面的研究发现, 单体基态和激发态的异构化反应一起可以形成四能级的分子电子体系, 而二聚体的却不能, 由此解释了单体和二聚体的紫外吸收光谱和荧光发射光谱均对应于酮式构型的原因. 利用混合含时密度泛函TD/MPW1PW91理论方法在溶剂存在下计算了标题物质的紫外吸收光谱和荧光发射光谱.     

喹吖啶酮光物理性质的理论表征

运用密度泛函理论对喹吖啶酮的光物理性质进行了研究. 结果表明, B3LYP/6-31G(d)//TD-B3LYP-PCM/6-311＋G(d)和CIS/6-31G(d)//TD-B3LYP-PCM/6-311＋G(d)方法能分别较好地描述喹吖啶酮的光吸收和光发射性质. 在吸收和发射的电子跃迁过程中, 主要是π-π*跃迁, 电荷在N和O之间的转移, 既包括单分子内的电荷跃迁, 也包括了通过氢键或π-π作用形成的二聚体的电荷跃迁. 溶剂对其光物理性质是有影响的, 这种影响是通过改变其前线轨道能来实现的, 受影响最大的是最高占据分子轨道(HOMO).     

Mono- and bichromatic electron dynamics: LiH, a test case

This paper describes an electron dynamics method where the time dependence of an external oscillating electric field is the perturbing part of the Hamiltonian. Application of the electric field induces charge movement inside the molecule and electronic transitions between the molecular orbitals. The test system is the neutral LiH molecule. The method is applied to wave functions calculated using the B3LYP (hybrid) density functional, with the STO-3G and the 6-31+G basis sets. The molecule undergoes full population inversion between the HOMO and the LUMO when the electric field is in resonance with the HOMO-LUMO energy gap. The magnitude of the electric field directly affects the rate at which electronic transitions occur and the rate at which charges move between lithium and hydrogen atoms. The method is used to model both monochromatic and bichromatic multiphoton effects in LiH. Monochromatic one-, two- and three-photon transitions occur between the HOMO, LUMO and two other virtual orbitals. There is evidence of both [1+2] direct and [1+1+1] stepwise multiphoton transitions. Bichromatically, two "laser" pulses are applied at different frequencies. Electronic transitions can be fine-tuned to occur via pre-specified pathways of virtual molecular orbitals.     

CF2BrCl分子近域轨道的电子动量谱学研究

The frontier molecular orbitals (HOMO and NHOMO) of CF2BrCl molecule have been firstly investigated by (e,2e) electron momentum spectroscopy. The experimental momentum profiles are compared with the theoretical profiles employing Hartree-Fock and density functional theory with 6-31G and 6-311+G(d) basis sets. Both HF and DFT calculations using 6-311+G(d) basis set can well describe the experiment, whereas those calculated using 6-31G basis set largely underestimate the experiment at the low momentum region. Furthermore, orbital electron density images show that HOMO and NHOMO have a mixed character of the bromine and chlorine lone pairs.     

Theoretical study on the hydrogen bonding of five-membered heteroaromatics with water

The hydrogen-bonding ability of five-membered heteroaromatic molecules containing one chalcogen and two heteroatoms with nitrogen in addition to chalcogen, respectively, have been analyzed using density functional and molecular orbital methods through adduct formation with water. The stabilization energies for all the adducts are established at B3LYP/6-31+G* and MP2/6-31+G* levels after correcting for the basis set superposition error by using the counterpoise method and also corrected for zero-point vibrational energies. A natural bond orbital analysis at B3LYP/6-31+G* level and natural energy decomposition analysis at HF/6-31+G* using MP2/6-31+G* geometries have been carried out to understand the nature of hydrogen-bonding interaction in monohydrated heterocyclic adducts. Nucleus-independent chemical shift have been evaluated to understand the correlation between hydrogen bond formation and aromaticity.     

外电场作用下寡聚苯分子导线的性质

利用Hartree-Fock 方法在6-31G*水平上对聚苯分子进行了计算研究. 分别从几何构型、分子轨道空间分布和分子轨道能级三个方面讨论了外电场对寡聚苯分子导线的影响, 给出了分子导线的性质与外电场的关系. 进一步, 连接硫原子于聚苯分子的两端, 并共价结合在金电极上. 利用非平衡格林函数方法对其在0-2.0 V 偏压下电子输运特征进行了深入研究.     

Electron momentum spectroscopy of CF2Cl2: experimental and theoretical momentum profiles for outer valence orbitals

Electron momentum distributions for outer valence orbitals of CF2Cl2 have been obtained by (e,2e) electron momentum spectroscopy at an incident energy of 1200 eV + binding energy. The experimental electron momentum profiles are compared with Hartree-Fock and density functional theory (DFT) calculations using B3LYP hybrid functional with the 6-31G and 6-311+G* basis sets. Generally, the shapes of the experimental momentum profiles are well reproduced by DFT calculations using larger basis sets 6-311 + G*. An attempt has been made to clarify the ordering of the outer valence orbitals, which have been in controversy, by comparing experimental results with B3LYP/6-311 + G* calculations.     

Probing furanose ring conformation by gas-phase computational methods: energy profile and structural parameters in methyl beta-D-arabinofuranoside as a function of ring conformation

The potential energy surface of methyl beta-D-arabinofuranoside (3) has been studied by ab initio molecular orbital (HF/6-31G) and density functional theory (B3LYP/6-31G) calculations via minimization of the 10 possible envelope conformers. The partial potential energy surface identified that the global minimum and lowest energy northern conformer was E(2). In the HF calculations, (2)E was the most stable southern conformer, while the density functional theory methods identified (4)E as the local minimum in this hemisphere. Additional calculations at higher levels of theory showed that the B3LYP-derived energies of many of the envelope conformers of 3 are dependent upon the basis set used. It has also been demonstrated that B3LYP/6-31+G//B3LYP/6-31G single point energies are essentially the same as those obtained from full geometry optimizations at the B3LYP/6-31+G level. The northern and southern minima of the B3LYP/6-31+G surface are, respectively, the E(2) and (2)E conformers. The B3LYP/6-31G geometries were used to study the relationship between ring conformation and various structural parameters including bond angles, dihedral angles, bond lengths, and interatomic distances.     

卡宾与醚C-H键插入反应的理论研究——(Ⅰ)卡宾与二甲醚的插入反应

用量子化学从头计算方法在MP2/6-31G(d)水平上计算了单重态的CH₂与二甲醚中C-H键插入反应的过程,并在MP₄/6-31G(d)水平上计算了反应物、过渡态和产物的能量。反应仅具有一个8.1kJ/mol的早期势垒,反应过程是卡宾的一个亲电-亲核过程,在插入过程中,卡宾空的p轨道和占有一对孤电子的σ轨道分别指向C-H键的H原子和C原子。     

Electronic, optical, and charge transfer properties of donor–bridge–acceptor hydrazone sensitizers

The ground state geometries have been computed by using density functional theory (DFT) at B3LYP/6-31G*, B3LYP/6-31G**, and PCM-B3LYP/6-31G* level of theories. The highest occupied molecular orbitals (HOMOs) are delocalized on whole of the molecule and the lowest unoccupied molecular orbitals (LUMOs) are localized on the tricarbonitrile. The lowest HOMO and LUMO energies have been observed for Dye1 while highest for Dye4. The LUMO energies of Dye1–Dye4 are above the conduction band of TiO₂ and HOMOs are below the redox couple. The absorption spectra have been computed in solvent (methanol) and without solvent by using time-dependant DFT at TD-B3LYP/6-31G*, TD-B3LYP/6-31G**, and PCM-TD-B3LYP/6-31G* level of theories. The calculated maximum absorption wavelengths of the spectra in methanol are in good agreement with experimental evidences. The maximum absorption wavelengths of new designed sensitizers are red shifted compared to parent molecule. The electronic coupling constant and electron injection have been computed by first principle investigations. The improved electronic coupling constant and electron injection revealed that new modeled systems would be efficient sensitizers.     

A combined semiempirical-DFT study of oligomers within the finite-chain approximation, evolution from oligomers to polymers

A computationally cheap approach combining time-independent density functional theory (TIDFT) and semiempirical methods with an appropriate extrapolation procedure is proposed to accurately estimate geometrical and electronic properties of conjugated polymers using just a small set of oligomers. The highest occupied molecular orbital-lowest unoccupied molecular orbital gap (HLG) obtained at a TIDFT level (B3PW91) for two polymers, trans-polyacetylene--the simplest conjugated polymer, and a much larger poly(2-methoxy-5-(2,9-ethyl-hexyloxy)-1,4-phenylenevinylene (MEH-PPV) polymer converge to virtually the same asymptotic value than the excitation energy obtained with time-dependent DFT (TDDFT) calculations using the same functional. For TIDFT geometries, the HLG is found to converge to a value within the experimentally accepted range for the band gap of these polymers, when an exponential extrapolation is used; however if semiempirical geometries are used, a linear fit of the HLG versus 1/n is found to produce the best results. Geometrical parameters are observed to reach a saturation value in good agreement with experimental information, within the length of oligomers calculated here and no extrapolation was considered necessary. Finally, the performance of three different semiempirical methods (AM1, PM3, and MNDO) and for the TIDFT calculations, the performance of 7 different full electron basis sets (6-311+G**, 6-31+ +G**, 6-311+ +G**, 6-31+G**, 6-31G**, 6-31+G*, and 6-31G) is compared and it is determined that the choice of semiempirical method or the basis set does not significantly affect the results.