SN2反应X-l+CH3XrXlCH3+X-r(Xl=Xr=F, Cl, Br, I)的价键方法研究

应用最近发展的价键组态相互作用(VBCI)方法计算了SN2反应X-l+CH3Xr→XlCH3+X-r(Xl=Xr=F, Cl, Br, I)的反应能垒和价键相关参数. 计算结果表明, VBCI能垒与采用分子轨道理论的CCSD(T)方法计算的能垒相一致. 讨论了SN2反应的反应参数.     

Valence bond theoretical study for chemical reactivity

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Ni/Pb(Zr,Ti)O3/TbFe2层状复合材料的谐振磁电特性研究

采用化学镀和黏接法制备层状磁电复合材料Ni/PZT/TbFe₂,研究其磁电性能及谐振频率随Ni层厚度的变化情况. 结果表明:Ni/PZT/TbFe₂层状磁电复合材料与其他结构的磁电性能不同,其一阶弯曲谐振峰值和纵向谐振峰值都很大. 随着Ni层厚度的增加,Ni/PZT/TbFe₂层状磁电复合材料的一阶纵向谐振峰值逐渐增大. 结合实验数据和理论计算值得出了材料的一阶弯曲谐振频率fr1和一阶纵向谐振频率f 关键词： 磁电效应 正磁致伸缩 负磁致伸缩 谐振频率     

价键方法中的非活性轨道优化新算法

本文通过引进一组正交的辅助非活性轨道和与它正交的辅助活性轨道,将价键理论方法中的冻核近似推广到轨道非正交的情形,得到了体系能量及其对非活性轨道的梯度解析表达式,简化了价键自洽场方法中非正交轨道能量梯度的计算．该方法的标度为（Na＋1）m^4,其中Na和m分别是活性轨道和基函数的个数．分析表明,与现有的其他算法相比较,该方法具有更低的计算标度,因而计算效率更高．     

Orbital deletion procedure and its applications

The orbital deletion procedure is introduced, which is suited to quantitatively investigating the electronic delocalization effiect in earboeations and boranes. While the routine, ab initio molecular orbital methods can generate wavefunetions for real systems where all electrons are delocalized, the present orbital deletion procedure can generate wavefunctions for hypothetical reference molecules where electronic delocalization effect is deactivated. The latter wavefunetion normlly corresponds In the most stable resonance structure in terms of the resonance theory. By comparing and analyzing the delocalized and the localized wavefunetions, one can obtain a quantitative and instinct pieture to show how electronic deloealizalion inside a molecule affects the molecular structure, energy as well as other physical properties. Two examples are detailedly discussed. The first is related to the hypercoujugation of alkyl groups in carbocations and a comparison of the order of stability of carbocations is made, T     

Ab initio VB Studies of the Ground and Low-lying Excited States of BeH and BH

A scheme has been proposed to classify valence bond(VB) wave functions for the calculations of ground and excited states,according to the symmetry properties of one-electron orbitals which are involved in the construction of VB wave functions.This scheme is illustrated by the examples of BeH and BH.Ab initio VB computations of these two test molecules in combination with the present classification scheme give reliable results.For example,calculation results show that the state C2∑ of BeH is stable,with the bonding energy 0.87 eV and bond length 0.238nm,which are in good agreement with those obtained by Gerratt et al.The bonding features of ground and low-lying excited states of BeH and BH are discussed.     

分子激发态的价键理论研究——B_2分子低激发态的成键特征

根据分子轨道理论与价键理论对化学键描述的对应关系,实现了双原子分子低激发态的价键描述和ab initio价键计算,B_2分子低激发态的计算结果表明,价键计算不仅具有清晰直观的物理意义,而且对位能面平衡点附近特征的模拟,优于分子轨道理论,包含几个激发键表的计算,便能正确地反映体系的电子相关效应.     

Pdn(n=2～13)团簇的密度泛函理论研究

采用密度泛函理论B3LYP方法计算并讨论钯原子团簇Pdn(n=2～13)结构模型.通过对钯原子团簇进行几何构型优化和振动频率计算,找出团簇总能量最低的同分异构体.由于Jahn-Teller效应的存在,团簇的最稳定结构采取对称性较低的几何构型.在钯原子数相同时,往往存在多个能量极为相近的稳定构型.单位原子平均静态极化率呈奇偶变化.     

HNC（←→）HCN成键特征的价键理论

采用现代价键理论之一的键表酉群方法, 结合Pauling的共振理论, 建议了一个选择重要价键结构的方案. 该方案能获得可靠直观的化学反应成键图象. 对异构化反应HNCHCN进行了成键特征的价键理论研究, 在从头算水平上解释了一些重要的成键特征, 如HCN比HNC稳定, 反应中CN键先伸长后缩短及反应中只有H迁移变化, CN键始终未断裂等. 计算结果表明, 只需少量价键结构就可对此异构化反应给出直观清晰的物理图象.