有机分子的自洽场分子轨道从头计算的通用程序和C,H基组的选择

本文介绍一个适用于中小有机分子的自洽场分子轨道(SCFMO)从头计算通用程序,并对各种C、H基组作了比较研究,提出一个新的最小原子轨道基组。用它试算甲烷分子的电子结构,仅用9个原子轨道(AO)和41个GTO,得到的分子总能量为E=-40.1662hartree,比STO-KG的结果为优。例如STO-6G用9AO-54GTO得到E=-40.1011hartree。甚至比国际通用的Gaussian-70程序所采用的4-31G双ζ基组也有改进,后者用17AO-36GTO得到E=-40.1395hartree。此外,还在S.B.双ζ基组的基础上,在C-H键中间外加浮动键轨道,得到E=-40.1930hartree。     

孪函数多电子基组在LiH分子方面的应用

选择从头算STO-6G基组,以孪函数Ⅳ电子基组计算LiH分子的基态(s=0)和激发态(s=1).结果表明,无需全部孪函数N电子基组,只要适当选择少数基组即可达到所需精度.     

NMR偶合常数的从头算级别自然杂化轨道研究

为了研究自然杂化轨道计算结果与核自旋偶合常数的相关性,本文进行了从头算级别的自然杂化轨道计算。采用STO－3G基组,利用Lowdin正交化原子轨道基组下的密度矩阵,得到了分子中各原子的杂化轨道、净电荷与^13C-H、^13C-^13C键自旋偶合常数^1Jcn和^1Jcc之间关系式。利用这些式子计算得到的结果与实验数据非常一致。     

从头计算中的多中心GTO基组

本文提出了用于LCA-MO-SCF从头计算的多中心GTO基组,编制了使用这种基组的ab initio FORTRAN IV通用计算程序ABHF,在能量、偶极矩、维里值,尤其是Hellann-Feynman力的计算方面,都比已有的STO-GTO系的基组好.     

轨道和波函数

分子（或原子）轨道是化学的基本概念之一。本文从Bohr原子轨道入手,介绍轨道概念的演化,以及轨道与波函数之间的关系,分子轨道与原子轨道之间的关系,并结合量化计算介绍基组与分子轨道的关系。     

铜锌金属天然酶活性中心量子化学计算

以菠菜叶中天然超氧化物歧化酶（SOD）铜锌活性中心及人为去掉金属锌的活 性中心为模板，运用Gaussian 94量子化学程序，在B3LYP/LANL2DZ基组水平上进行 了计算，获得了分子轨道能量、电荷分布以及原子轨道对前沿分子轨道贡献的信息 。结果表明，金属铜对于催化歧化超氧阴离子O_2~-具有至关重要的作用，而金属 锌起到稳定结构和促成构建活性中心的作用。     

d原子轨道的形状究竟是怎样的?

氢原子轨道的概念是高等学校化学中的一个基础概念,但由于大家都是通过原子轨道的经向分布图和角度分布图来把握轨道(以及电子云)的形状的,这种把握往往不见得准确。这里,作者提供在研制“分子波函数等值面投影图绘图程序”过程中,所绘得的各氢原子轨道的电子云界面图或等值面图(见下图),这些图形清楚地反映了轨道形状的细节。特别有趣的是d原子轨道。与以往介绍的d轨道     

铁超氧化物歧化酶活性中心结构研究

对氧化型、还原型及非活性形式铁超氧化物歧化酶Fe-SOD活性中心进行了量子化学计算和比较。在HF方法及LANL2DZ基组水平上获得了分子轨道能量、电荷分布以及原子轨道对前沿分子轨道贡献的信息。结果表明, Fe-SOD酶的活性形式的活性中心易于接受超氧自由基(O2- )的进攻而完成其生理功能。     

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.     

关于弥散函数的几个结果

讨论了关于应用弥散函数对分子负离子进行从头算的几个结果。采用线性拟合法确定了一些基组的弥散函数轨道指数值,这些值与优选值十分接近。     

六核簇离子Te64+和P64-的电子结构与化学键

本文用EHMO法计算六核簇离子Te₆⁴⁺和P₆^4-的电子结构。分析与它们相同构型的棱柱烷C₆H₆和苯在成键性质上的差异。结果表明,这两簇离子的多余价电子填充到能级略高于自由原子p轨道的弱反键分子轨道。     

An efficient closed-shell singles and doubles coupled-cluster method

A reformulated set of equations for the closed-shell singles and doubles coupled-cluster (CCSD) method is presented. A computational cost of n_v⁴n₀²+7n_v³n₀³+1n_v²n₀⁴ for the n⁶ steps is obtained, where n_v is the number of virtual molecular orbitals included in the CCSD procedure, n₀ is the number of doubly occupied molecular orbitals and n=n₀+n_v. Test calculations for the cis and trans isomers of FNNF and planar and pyramidal CH₃⁻ are presented. Equilibrium structures determined with large Gaussian basis sets at the second-order Møller-Plesset (MP2) perturbation level of theory are reported and used for the other electron correlation methods. With the largest one-particle basis set (144 contracted Gaussian functions), the equilibrium geometries of cis- and trans-FNNF agree with experiment. Based on analyses of planar and pyramidal CH₃⁻ wavefunctions and the calculated inversion barrier, it is suggested that the molecular anion may not exist in a planar configuration but that autodetachment of an electron occurs before the transition state is reached. Comparisons of our new CCSD procedure demonstrate that coupled-cluster methods are not significantly more expensive than similar electron correlation techniques.     

计算化学在分子轨道教学中的应用

分子轨道理论是理解分子电子结构与微观性质的重要理论之一,也是本科生与研究生结构化学教学中的重点与难点。学生对原子轨道组合形成分子轨道、分子轨道能级交叉混合等知识的理解缺乏形象直观、定量的认识。本文通过基于量子化学或密度泛函理论的Gaussian 03计算软件,计算、绘制并分析了F_2、O_2、N_2、HF、CO等的分子轨道能级图,将学生较难理解的内容定量、直观地呈现出来,形象地解释了分子轨道成键原则与电子填充原则等分子轨道理论中的重难点,加深了学生对分子轨道理论的理解,特别是sp轨道混杂导致的σ_(2p_z)与π_(2p)轨道能级交叉这一难点,激发了学生学习的主动性和积极性,提高了教学质量。在此基础上,利用分子轨道理论分析了CO_2的电子结构,使学生学会应用分子轨道理论解决实际问题,巩固了相关课堂理论知识。     

Inner-shell and valence-shell electronic excitation of SF6, SeF6 and TeF6 by high energy electron impact: An investigation of potential barrier effects

Inner- and valence-shell electron energy loss spectra of gaseous SF₆, SeF₆ and TeF₆ have been measured at high impact energy (2.0–3.7 keV) and zero degree scattering angle. The resulting inner-shell excitation spectra include F 1s, S 2s and 2p in SF₆: F 1s, Se 3s, 3p and 3d in SeF₆ and F 1s, Te 4s, 4p, 4d and 3d in TeF₆. The results for each of these hexafluorides are interpreted, in the framework of the potential barrier model, as excitations to resonances involving a common manifold of virtual valence (inner-well) orbitals and also to Rydberg (outer-well) orbitals. The below-edge shape resonances in corresponding inner-shell excitation spectra of these hexafluorides show very similar variations in intensities in accord with expectations based on electric-dipole selection rules. This is an indication that these below-edge resonances in SeF₆ and TeF₆ are of the same symmetry as those in SF₆ (i.e. a_1g and t_1u). The continuum (above-edge) shape resonances in SeF₆ also show similar spectral behavior to those of SF₆ and can be understood by including Se 4d and S 3d orbitals in the basis for the respective MO schemes. However, in TeF₆ completely different spectral behavior is observed for the continuum resonances. In particular, there is a dramatic series of intense resonances observed above the Te 3d and 4d edges. The TeF₆ spectrum can only be understood by extending the MO basis set to include the Te 4f orbitals which are even lower lying than the Te 5d orbitals. Therefore, these continuum resonances which are also seen in the F 1 s and Te 3p spectra of TeF₆ are assigned to l=3 (f-type) continuum shape resonances due to involvement of the 4f orbitals rather than the l=2 (d-type) continuum resonances observed in SF₆ and SeF₆. This is the first reported observation of such f-type continuum shape resonances and such considerations will likely prove to be important in the understanding of near-edge spectra of heavy atom containing species. The VSEELS spectra which are very similar for the three hexafluorides also show significant continuum shape resonances. A consideration of both the ISEELS and the VSEELS spectra indicates that there is a weakening of the potential barrier in going through the series from SF₆, SeF₆ to TeF₆.     

基于二噻吩并吡咯π桥的窄带隙非富勒烯受体材料在有机太阳能电池中的应用

以不同烷基取代的二噻吩并吡咯(DTP)为π桥,连接吲哒省并二噻吩(IDT)中间单元和氰基茚酮(IC)或二氟代氰基茚酮(2F-IC)末端基团,设计并合成了6个窄带隙的非富勒烯受体材料。 其中,IDTDTP-C₂C₂-H和IDTDTP-C₂C₂-F中的DTP单元以1-乙基丙基为侧链,IDTDTP-C₆C₆-H和IDTDTP-C₆C₆-F中的DTP单元以1-己基庚基为侧链,IDTDTP-C₁₂-H和IDTDTP-C₁₂-F中的DTP单元以十二烷基为侧链。 6个分子均具有较窄的光学带隙(1.37~1.44 eV)。 相比于以IC为末端基团的分子(IDTDTP-C₂C₂-H、IDTDTP-C₆C₆-H和IDTDTP-C₁₂-H),由于氟原子的拉电子效应,以2F-IC为末端基团的分子(IDTDTP-C₂C₂-F、IDTDTP-C₆C₆-F和IDTDTP-C₁₂-F)具有红移的吸收光谱,以及更低的最高分子占有轨道能级(HOMO)和最低分子空轨道(LUMO)能级。 以宽带隙聚合物聚[2,6-(4,8-双(5-(2-乙基己基))噻吩-2-基)-苯并[1,2-b:4,5-b']二噻吩-alt-5,5-(1',3'-二-2-噻吩)-5',7'-双(2-乙基己基)-苯并[1',2'-c:4',5'-c']二噻吩-4,8-二酮](PBDB-T)为给体材料,制备了有机太阳能电池器件。 PBDB-T:IDTDTP-C₆C₆-F共混薄膜具有较高且更平衡的空穴/电子迁移率,以及良好的形貌,基于PBDB-T:IDTDTP-C₆C₆-F的有机太阳能电池获得了6.94%的能量转换效率,开路电压为0.86 V,短路电流密度为13.56 mA/cm²,填充因子为59.5%。     

过渡金属杂硼烷结构规则的量子化学计算

用EHMO量子化学计算方法,计算了过渡金属杂硼烷骨架Fe_{nB6-n(n=0,1,…,6),验证和讨论了过渡金属杂硼烷的价成键和价非键轨道数BMO+NBMO=4n1+9n2-F。其中n1、n2和F都只与骨架的几何性质有关。}     

氨基酸修饰的手性多酸的电子结构和光学活性的理论研究

采用密度泛函理论(DFT)方法研究了L-O₂CCHCH₃NH₃(L-Alanine)修饰的手性多酸[Se^ⅣMo₆O₂₁(L-alanine)₃]^2-, [Sb^ⅢMo₆O₂₁(L-alanine)₃]^3-及[Bi^ⅢMo₆O₂₁(L-alanine)₃]^3-的几何结构、电子结构以及紫外-可见(UV-Vis)谱和电子圆二色(ECD)谱.通过对电荷转移跃迁性质的分析, 探讨了多酸中杂原子对手性光学性质的影响.结果表明, 杂原子(Se, Sb, Bi)对多酸的几何结构影响较大, 且对该类体系的UV-Vis谱的吸收峰的强度和峰形都有显著的影响.其ECD谱的转动吸收方向和强度以及吸收峰位和峰形也因杂原子的不同而发生明显变化.低能区UV-Vis谱和ECD谱的产生主要源自多酸中氧原子的p轨道到Mo原子d轨道的电荷转移跃迁, 而对于高能区的UV-Vis谱和ECD谱的产生, 则主要为多酸中杂原子以及与杂原子直接相连的氧原子p轨道到Mo原子d轨道的电荷转移跃迁.     

Quantum Chemistry Studies on the Heteropoly Blues of Molybdosilic Series with α-Keggin Structure

ＱｕａｎｔｕｍＣｈｅｍｉｓｔｒｙＳｔｕｄｉｅｓｏｎｔｈｅＨｅｔｅｒｏｐｏｌｙＢｌｕｅｓｏｆＭｏｌｙｂｄｏｓｉｌｉｃＳｅｒｉｅｓｗｉｔｈα－ＫｅｇｇｉｎＳｔｒｕｃｔｕｒｅＦＵＱｉａｎｇ,ＹＡＮＧＭｉｎｇ,ＣＨＥＮＢｉｎ,ＷＡＮＣＥｎ－Ｂｏ,ＸＩＥＤｅ－...     

建立在群对称轨道(SMO)及特征组态(CD)基础上的线性分子SMO-CDCI方法

定义和讨论了线性分子的群对称轨道(SMO)及特征组态函数(CD),它能够对线性分子的分子轨道与组态函数进行简单而完全的对称分类.SMO－CDCI方法是一种高效的计算方法,大大节省了线性分子CI计算的机时与内存.     

Theoretical study of C24N4 molecule

Both ab initio 6-31G, 3-21G and STO-3G basis sets and semiempirical PM3 and AM1 molecular orbital calculations are carried out on the C₂₄N₄ molecule of the T_d symmetry group. Results on the fully optimized structure which constrained T_d symmetry, molecular orbitals and vibrational frequency were obtained by both ab initio and semiempirical methods. The binding energy and various thermodynamic properties were also calculated via the PM3 and AM1 semiempirical methods. All the evidence of this work proves that the C₂₄N₄ molecule is stable and that its four six-membered rings with a remarkable delocalized C…C bond are similar to the related rings in the C₆₀ buckminsterfullerene structure.