直链烷烃体系电子转移的价键方法研究

应用价键理论研究直链烷烃体系的电子转移过程, 直接计算得到的耦合能与实验值以及其它的理论计算结果一致. 对于阳离子系列, BOVB方法和VBCIS方法都给出了与实验相符的计算结果, 但对于阴离子系列, VBCIS方法的β值基本一致, 而BOVB方法的β值较大. 计算结果表明, 价键理论可以应用于电子转移的理论研究, 而VBCIS方法是研究电子转移问题的一种合适的价键计算方法.     

经典价键理论的从头算计算方法

价键理论是两大现代化学键理论之一,广泛应用于化学键本质和化学反应机理的研究。由于计算困难,价键理论应用局限于定性的讨论而无法有效地开展从头计算研究。现代经典价键理论在经典价键理论的理论基础上,引入合理有效的计算方法,提高了价键计算的效率。本文回顾近年来经典价键理论从头算方法在提高计算精度和拓展研究范围方面的发展,并简要展望价键理论方法的发展趋势。     

钨氧键价参数的研究

根据键价理论中的指数方程s_ij=exp[(R_o-r_ij)/B],利用晶体结构报告中不同氧化态n的329个W-O键长数据,选取不同的B值对键价参数R₀进行了拟合,建立了一系列R₀-n线性方程,并进而得到与W氧化态无关的键价参数R₀=0.1896 nm和B=0.028nm.与文献数据比较,本文拟合的键价参数取得了较好的键价和计算结果,讨论了几个应用的实例.     

镧系元素相关的键价参数研究

根据镧系元素络合物的晶体结构数据确定了单价键长R0的镧系收缩效应,并对已有的键价参数进行了系统的修订.建立了Ln-O键的R0对原子序数N在普适参数B=0.037 nm下的线性方程R0(nm)=0.2879－0.00132N.用不同参数进行键价和的计算并对结果进行了对比和讨论,最后展望了相关研究的前景.     

HSO自由基电子基态激发态的CAS计算研究

使用CASSCF方法和ANO-L基组优化了HSO自由基的基态和3个低占据激发态的结构, 并采用包括更多电子动态相关能的CASPT2方法进行了单点能校正. 频率计算结果表明, 优化的4个几何为势能面上的稳定点. 通过电子结构的研究合理地解释了各个激发态相对于电子基态的结构变化.     

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.     

S_N2反应X_l~-+CH_3X_r→X_lCH_3+X_l~-(X_l=X_r=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 +CH3 Xr→ Xl CH3 +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 .     

酞菁基态和激发态的计算

采用DFT方法在B3LYP/6-31G水平上得到了H2Pc(酞菁)的优化结构,并在此基础上采用TDDFT方法计算了激发态.通过与H2P(卟吩)、H2Pz(四氮卟吩)和H2TBP(四苯并卟啉)的比较,研究了苯并取代以及氮杂取代对H2Pc的分子轨道和激发态的影响,上述取代效应使得H2Pc的HOMO-1(132 b1u)和HOMO-3(130 b1u)轨道发生了翻转,氮杂取代的影响尤其明显.这两种取代都使得Q带振子强度增大,在这四种化合物中,H2Pc的振子强度最大.TDDFT计算结果与实验值符合得较好.     

Excited States of Conjugated Hydrocarbons Using the Molecular Mechanics - Valence Bond (MMVB) Method: Conical Intersections and Dynamics

We developed the molecular mechanics—valence bond (MMVB) method following an original suggestion of Jean-Paul Malrieu and coworkers. By coupling a parameterized Heisenberg Hamiltonian to a standard classical force field (MM2), reliable ground and excited state geometries of conjugated hydrocarbons can be rapidly optimized. The MMVB method was central to our development of algorithms for locating conical intersections and calculating their associated decay dynamics. Here, we briefly review the chemical applications of MMVB to date, and present two new studies using the photostability of pyracylene and the excited state decay dynamics of the photochromic dihydroazulene/vinylheptafulvene (DHA/VHF) reaction.     

价键理论的不变式方法的新算法

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...     

Deactivation of Excited States

Nature abhors an electronically excited state and strives to convert this energy to other forms. This article is concerned with the various pathways involved in the degradation of electronic excitation to ordinary “thermal” forms, but will primarily discuss the quenching of excited states by other molecules. The authors include as examples only those phototransformations and interactions encountered in solution.     

NH_2基态和激发态的SAC－CI和量子拓扑方法研究

ＮＨ_２基态和激发态的ＳＡＣ－ＣＩ和量子拓扑方法研究郑世钧，蔡新华，宋天乐，孟令鹏，中迁博，波田雅彦（河北师范学院化学系，石家庄，０５００９１）（京都大学工程学院京都，日本）关键词ＳＡＣ－ＣＩ方法，激发态，电子密度，拓扑分析用量子拓扑学方法研究激发态...     

Valence Bond – Rebirth of the Phoenix or Relic from the Stone Age

The valence bond (VB) method has enjoyed its prime time during the early stages in the field of quantum chemistry. After the advent of molecular orbital methods VB lost its popularity but continued to be improved and refined by a small community of scientists who appreciated its power of revealing insight into the origins of chemical reactivity. This review summarizes the developments of the VB theory in the past few decades by focusing on two major areas of research: studies of the reactivity of small chemical systems and discovering the origins of enzyme catalysis. In both cases the unique capabilities of VB that facilitated discoveries of new concepts in an elegant and seemingly effortless way are discussed. It is suggested that owing to the success of these discoveries VB methodology is once again steadily gaining momentum. It is believed that VB concepts will play a major role in the future of theoretical chemistryElectronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.Affiliated with the David R. Bloom Center for Pharmacy at the Hebrew University     

B2分子的单激发态与强束缚多激发态

双原子分子电子态的实验信息主要来源于基态或低激发态的单光子吸收光谱。激发态与基态相比,通常呈现出弱的成键特征,即平衡核间距增大,振动频率降低。但关于双原子分子多激发态性质的研究较少。近年来,随着多光子技术,特别是共振放大多光子电离(Resonance enhanced multiphoton ionization)光谱学的发展,运用精确的理论计算研究其多激发态的性质有十分重要意义。     

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Ｈ２、Ｌｉ２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。     

Solid-State Photochemistry—A Method of Generating Unusual Valence States

High-energy radiation can give rise to pairs of complementary defects in nonmetallic solids by the transfer of electrons between various types of atoms. These “color centers” which are generally paramagnetic, can usually be described as unusual valence states of an element. They are destroyed by heating and in most cases regenerated by renewed irradiation. In a heteropolar solid the formation of color centers usually leads to cancellation of point charges due to foreign ions of other valence or to vacancies. This is shown by the examples of kunzite, brazilianite, smoky quartz, and citrine; the most important methods for the structural elucidation of color centers are also described. Application of the principle of charge balance opens up possibilities for the production of unusual valence states, e.g. Al²⁺, F^2?, Fe⁴⁺, and O^?. Moreover, the type of the color center often permits far-reaching conclusions to be drawn about the defect structure of real crystals, which could hardly be clarified in other ways.     

One- and Two-Dimensional Torsion-Inversion Models for the Fluoral Molecule (CF3CHO) in Excited Electronic States

The structure of the conformationally nonrigid fluoral molecule (CF₃CHO) in the ground (S₀) and lowest excited triplet (T₁) and singlet (S₁) electronic states was studied by ab initio quantum-chemical methods. The equilibrium geometric parameters and harmonic vibrational frequencies of the molecule in these electronic states were determined. The calculations demonstrated that the electronic excitation causes substantial changes in the molecular structure involving the rotation of the CF₃ top and the deviation of the CCHO carbonyl fragment from planarity. The quantum-mechanical problems for large-amplitude vibrations, namely, for the torsional vibration in the S₀ state and the torsional and inversion vibrations (nonplanar carbonyl fragment) in the T₁ and S₁ states, were solved in the one- and two-dimensional approximations. A comparison of the results of calculations revealed the correlation between the torsional and inversion motions.     

LiBe+分子基态及其低电子激发态

采用Davidson校正的多参考组态相互作用方法(MRCI+Q)和多参考平均二次耦合团簇方法(MRAQCC)结合基组ROOS-ANO-TZP得到了LiBe+分子基态(x1∑+)以及六个低电子激发态(a3Σ+,b3∏,A1∑+,B1∏,c3∑+,C1∑+)的势能曲线(PECs).计算结果表明:X1∑+,a3∑+,b3∏和...