对取代苯Ph一X（X＝F，OH，NH_2）的价键理论研究

采用键表酉群方法对Ｃ６Ｈ５Ｆ、Ｃ６Ｈ５ＯＨ和Ｃ６Ｈ５ＮＨ２中的电子离域现象进行了计算和分析，讨论了取代苯的价键描述特性，并计算了取代基的π电子离域能．结果表明离子结构成分与离域能有直接关系，即离子成分越多，电子离域能越大．／６－３１Ｇ基组及“分子中的原子”方法将电荷密度分区积分得到各原子上的电荷集居数，并将此结果与取代苯的反应性能进行了比较。为在价键意义上分析和理解取代基对苯环电子结构及其反应性能的影响，本文对３个典型的取代苯Ｐｈ－Ｘ（Ｘ＝Ｆ，ＯＨ，ＮＨ２）进行了初步的价键计算和讨论．１计算方法及构型在键表酉群方法中［５］，体系的一个共振结构可用一个价键结构函数即键表ψ（ｋ）来描述，相应的体系总波函数Ψ可表示为Ｍ个正则键表的线性组合：式（１）便构成了键表相互作用（ＢＴＩ）计算方法［６］的基础．键表对体系的结构贡献定义为：原子轨道ｑ上的电荷集居数定义为：式中ｍｑ（ｋ）可取０、１或２，分别对应于键表ψ（ｋ）中原子轨道ｑ出现０、１或２次．为简比计算，我们将取代苯的σ骨架用ＨＦ分子轨道固定［７］，这样仅需考虑π电子及轨道．原子轨道积分及ＨＦ－ＳＣＦ计算采用Ｇａｕｓｓｉａｎ８０程序．联系人及第一作者：莫亦荣，男，２９

A New Algorithm For the Permanent Approach to Valence Bond Theory

价键理论的不变式方法的新算法吴玮，莫亦荣，张乾二（厦门大学化学系，厦门，361005）关键词价键理论，群论，不变式近年来，我们提出了闭壳层的价键（Vb）计算的不变式（或称正行列式）方法［1，2］.将置换群Sn对Vb结构的对称子群Q进行陪集分解。每一个...Based on Ryser permanent expansion method, a new algorithm For the so-called permanent approach to valence bond theory is presented.With the new algorithm, Hamiltonian and overlap matrice elements are calculated directly, rather than by the“sequential”Laplace expansion method used in our previous work.The algorithm will be more easily implemented than that based on Laplace expansion method.国家自然科学基金;攀登计划资

大基组在价键计算中的处理

编写了普适性的多键表自洽场程序，该程序能对单电子轨道展开系数和键表系数同时优化，其中单电子轨道的展开空间可任意定义，实际计算建议采用“杂化”轨道形式，即每个单电子轨道只对一个原子的基函数展开，对Ｈ_２、Ｌｉ_２及ＨＬｉ采用不同基组进行计算，结果表明用３个键表自洽计算所得能量与ＭＰ２结果相近，且我们的计算对键的共价性和离子性分析非常直观

VB studies on bonding features of HNCHCN

Within the bonded tableau unitary group approach (BTUGA), a scheme, combined with Pauling抯 resonance theory to select the predominant valence bond structures for VB calculations, is proposed. This scheme ensures a reliable and illustrative bonding picture in the description of chemical reactions, as exemplified by the isomerization reaction HNCHCN. The computation results account for important bonding features about this isomerization at the ab initio level and explore the mechanism of phenomena such as (i) HCN is more stable than HNC; (ii) the C-N bond first lengthens and then shortens in the vicinity of the transition state; (iii) only H-atom migration is observed in the isomerization process, without the breaking of the CN bond. Our results demon-strate that only a few bonded tableau functions are sufficient enough to provide a visual and reli-able bonding picture

块定域波函数方法及其应用

提出了块定域波函数方法以定量分析分子内的电子定域现象或分子间的电荷传递效应.对于一个假想的严格定域的分子,我们通过将全部的电子和基轨道配分成几个子空间来构造其相应的波函数.其中每一个分子轨道只对某一个子空间展开,各子空间内的分子轨道相互正交,但不同子空间内的分子轨道间是非正交的.Hartree-Fock波函数和块定域波函数之间的能量之差即为分子内的电子定域能或分子间的电荷传递能.我们应用块定域波函数方法讨论了丁二烯分子中的旋转势垒

轨道去除方法及其应用

介绍了能对正碳离子及硼烷化合物中的电子离域现象作定量研究和分析的轨道去除方法 .一般的分子轨道方法能得到电子离域体系的波函数 ,而轨道去除方法则能得到电子离域效应被湮灭之后的假想定域体系的波函数 .通过对两者的对比分析 ,可定量而又清晰地了解分子内的电子离域是如何影响分子结构、能量及其他分子性质的 .具体讨论了正碳离子中烷基的超共轭现象和三卤化硼的Lewis酸性 .结果表明 ,轨道去除方法可非常有效地解释一些传统的化学问

Valence bond description for the ground state and several low-lying excited states of LiH

通讯作者地址:Mo YRThe potential energy curves of the ground and four singlet low-lying excited states of LiH were calibrated using the bonded tableau unitary group approach (BTUGA). The results show that the ground and the first excited states can be described quite well by only three bonded tableaux, namely [GRAPHICS] Of these three bonded tableaux, the first two consist of the covalent bond between the atomic orbital H1s and the hybrid atomic orbitals of Li2s and Li2p(z), while the last one corresponds to the ionic structure Li+H-. Further analyses showed that, compared with the covalent structures, the ionic structure Li+H- contributes less to the binding energy and the dipole moment of the ground state of LiH. This result differs from that based on MO theory. Our results clearly indicate that an electron will transfer from lithium to hydrogen in the range 5.0-7.0 a.u., which explains the so-called ''harpoon'' mechanism in the molecular-beam dynamics. A detailed and successful valence bond explanation for the variation curve of the dipole moment mu with respect to the distance R for the first excited state is also presented. There are two opposite effects, namely the contribution from the ionic structure Li+H- and the non-equivalent sp hybridization of the atomic orbitals on lithium, which make the dipole moment of the first excited state vary with R and lead the direction of mu to reverse at approximately 6.0 a.u. A brief discussion of the other three excited states is given

A new algorithm for the permanent approach to valence bond theory

Based on Ryser permanent expansion method, a new algorithm for the so-called permanent approach to valence bond theory is presented. With the new algorithm, Hamiltonian and overlap matrice elements are calculated directly, rather than by the ''sequential'' Laplace expansion method used in our previous work. The algorithm will be more easily implemented than that based on Laplace expansion method

现代价键理论研究进展

概述现代价键理论的几个主要方法 ,以及它们的特点和发展现状 .并重点介绍了对不变行列式方法和相应的计算程序

价键理论的对不变式方法——Ⅱ.无自旋价键计算程序Xiamen

发展完善了价键理论的对不变式方法,给出了对不变式的正则展开方法,并证明了对不变式可以展开成任意阶的子对不变式和相应余子式乘积的形式.利用对不变式方法,完成一个新的无自旋价键理论方法从头计算程序——Xiamen.测试计算表明,Xiamen程序比基于传统价键方法的程序计算效率高,为量子化学计算研究提供了一个新工具