电负性标度和电子亲和能的规律性研究II. 电子亲和能的规律性研究

本文研究了不同情形下, 绝对硬度η与~nt(r为轨道半径, n, I 为轨道的主量子数和角量子数)的关系, 并在前文提出的Z/~nl与Mulliken 电负性关系基础上, 将元素电子亲和能A同时与Z/~nl和~nl相关起来, 并表示成A=αZ/~nl+b~nb+c(a, b, c为常数)。我们研究了这种关系在周期表中各族及各过渡系的拟合结果, 不但计算值与电子亲和能的实验值非常吻合, 而且拟合的相关程度很高。本文方法为系统研究电子亲和能的变化规律提供了简单可行的途径。     

电负性标度与电子亲和能的规律性研究I. 价电子的平均核势

本文将价电子的轨道平均半径~n~l(n、l为轨道的主量子数和角量子数)引入电负性函数中,并采取与常规方法不同的方式确定有效核电荷数Z'。在此基础上,提出新的电负性标度-Z'/~n~l。该标度与Mulliken电负性有良好的线性关系,与Pauling电负性有大体上一致的周期性变化趋势。新标度有一定的物理含义,它代表价电子的平均核势,并且完全可由理论计算得到。     

电负性标度与电子亲和能的规律性研究I. 价电子的平均核势

本文将价电子的轨道平均半径~n~l(n、l为轨道的主量子数和角量子数)引入电负性函数中,并采取与常规方法不同的方式确定有效核电荷数Z'。在此基础上,提出新的电负性标度-Z'/~n~l。该标度与Mulliken电负性有良好的线性关系,与Pauling电负性有大体上一致的周期性变化趋势。新标度有一定的物理含义,它代表价电子的平均核势,并且完全可由理论计算得到。     

电子亲和势法判断负离子聚合单体的活性

提出了利用不同取代基烯类单体的电子亲和势来判断其负离子聚合反应活性的方法.采用密度泛函理论的B3LYP/6-31G(d)方法优化了不同取代基烯类单体几何构型,在B3LYP/6-311++G(3df,2p)水平上计算了其电子亲和势.通过电子亲和势计算值与文献报道实验数据比较,表明本文采用的计算方法是比较可靠的.结合不同取代基烯类单体的电子亲和势的计算结果,通过与Q-e关系及取代基常数σ数据进行比较表明,电子亲和势可以用来判断不同单体负离子聚合反应的活性高低.     

原子外层轨道能级与电子的电离顺序

本文根据光谱实验结果和量子数意义,归纳出一个n、1规则:E=n+1-(1-0.75)/(1+1)。n为主量子数,l为角量子数。计算的E值大小,可用来判别原子外层轨道能级高低顺序,确定原子核外电子的电离顺序,预测新的元素周期等。     

电子亲和能周期性浅议

在列举电子亲和能文献数据的基础上,对数据的可靠性进行了讨论,给出原子的电子亲和能随原子序数周期性变化的新图示,并且对某些异常的数据作了解释.     

有机半导体的电子电离能、亲和势和极化能的密度泛函理论研究

准确预测有机半导体的能级(如电子电离能和亲和势等)对设计新型有机半导体材料和理解相关机理至关重要。从理论计算的角度看,主要挑战来自于缺少一种不仅能够在定性上合理而且在定量上精确预测,同时并不显著增加计算成本的理论方法。本文中,我们证明了通过结合极化连续介质模型(PCM)和"最优调控"区间分离密度泛函方法能够准确预测一系列有机半导体的电子电离能(IP)、亲和势(EA)和极化能,其预测结果与实验数据吻合得很好。重要的是,经过调控后分子的前线分子轨道能量(即-~εHOMO和-~εLUMO)与对应的IP和EA计算值很接近。调控方法的成功可以进一步归因于其能够根据不同分子体系或同种分子所处的不同状态(气态和固态)"最优"地平衡泛函中分别用于描述电子局域化和离域化的作用。相比而言,其它常见的密度泛函方法由于包含的HF%比例过低(如PBE)或过高(如M06HF和未调控的区间分离泛函),均不能给予合理的预测。因此,我们相信这种PCM-调控的方法能够为研究其它更加复杂的有机体系的能级问题提供一种更加可靠和便捷的理论工具。     

二氯吗啉双胍合铜(Ⅱ)的分子结构和电子结构

本文报道二氯吗啉双胍合铜的晶体结构和电子结构研究。晶体属单斜晶系,空间群P2_1/n。晶胞参数:a=7.739(2)A,b=11.593(3)A,c=12.347(3)A;β=96.43°(2),Z=4,晶胞体积V=1100.78A,理论计算密度Do=1.844g·cm~(-3)。用重原子法及差值Fourier合成解出结构,最后的R值为0.044。每个分子中,Cu(Ⅱ)为四配位的平面四边形构型,两个Cl-处于顺式。吗琳双胍中的两个N原子与Cu(Ⅱ)螯合成共平面的六员环,螯合环及环外C-N键间形成共轭π键。用CNDO/2方法研究了配合物的电子结构。     

推/拉电子取代基对PCBM结构及光谱性质影响的理论研究

应用密度泛函理论(DFT)方法计算[6,6]-苯基-C₆₁-丁酸甲酯(PCBM)及其苯环对位取代得到的4种衍生物的几何和电子结构. 采用第一激发能校正了分子的最低未占据分子轨道(LUMO)能级, 探讨了推/拉电子基团对分子前线轨道的影响. 在全优化几何构型的基础上, 采用含时密度泛函理论(TD-DFT)方法研究了电子吸收光谱特征和电荷转移态性质, 并讨论了推/拉电子基团对体系电子吸收光谱性质的影响. 通过对重组能和电子亲和势的计算, 预测了PCBM与4种衍生物的电子能力及电子迁移率大小的关系. 结果表明, 在PCBM中, 在苯环的对位引入推电子基团可以提高分子的前线轨道能级, 改变前线轨道电子云分布, 明显增强可见光范围内的吸收强度, 增加可见光范围内的电荷转移吸收, 且激发态的电荷转移随着引入基团推电子能力的增加而增强. 化合物5的激发态分子内电荷转移性质最强, 且具有较独特的光伏性质. 而在同样位置引入拉电子基团, 则降低了分子前线轨道能级对电子吸收光谱的影响.     

钒、铬团簇的电子亲合能、硬度与原子数的关系

根据静电球形液滴模型理论和离子极化、屏蔽效应对团簇的影响, 推导适合钒、铬团簇电子亲合能、硬度与原子数关系符合的普遍公式: Y=ae2/R+b/R2+c, R=rsN1/3, 从而更方便地预测大尺寸团簇的性质参数, 并发现和分析结构和性质异常的小团簇, 如Vn(n=5, 7, 9, 13)和Crn(n=6, 10, 17)的性质.     

The evaluation of molecular electron affinities

The performance of a variety of levels of theory in evaluating molecular electron affinities (EAs) has been systematically examined. Calculations have been carried out for six different basis sets and for nine theoretical procedures including unrestricted (UHF) and restricted (RHF) Hartree-Fock theory, Møler-Plesset perturbation theory (UMP2, UMP3, UMP4), configuration interaction (UCISD, RCISD, RCISD(Q)) and equations-of-motion (EOM) approaches. Electron affinities were evaluated for CH₃, NH₂, OH, F, C₂H, CN, BO, N₃, OCN, and NO₂. Very poor results are generally obtained unless diffuse functions are included in the basis set and electron correlation is incorporated. Even with the largest basis set used in the present study (6-311 + + G(2d, 2p)), there are still residual errors greater than 0.2 eV (UMP4) or 0.6 eV (CISD) in the absolute EAs. However, better results are obtained under certain circumstances for relative EAs. The results appear to be significantly affected by spin contamination in the UHF wave-functions. For those systems for which spin contamination is small, best absolute values of the EAs generally come from the EOM and UMP2 calculations, whereas the most constant errors (thereby allowing systematic correction) are found at the UMP4, CISD, and RCISD(Q) levels. For the systems for which spin contamination is larger, best results are obtained with the CI-based procedures (CISD and RCISD(Q)). The errors in calculated EAs for the molecules with differing electronic characteristics can vary quite widely. Caution must therefore be exercised before applying schemes which rely on a constancy of errors to estimate electron affinities. The UMP procedures appear particularly suspect in this regard if spin contamination is significant. The RCISD(Q) approach is recommended under such circumstances.     

Ionization potentials,electron affinities,electronegativities, and hardnesses of fractional charged atoms from the density-functional theory

The electron-correlation and self-interaction corrected generalized exchange local-spin-density functional theory with the Gopinathan, Whitehead, and Bogdanovic Fermi-hole parameters has been employed to give self-consistent field calculations for the quark atoms, the first- and second-order positive ions, and the first- and second-order negative ions of the quark atoms with fractional nuclear charges $ Z = N \pm \frac{1}{3} $ and $ Z = N \pm \frac{2}{3} $. A special technique to obtain the converged second-order negative ions is discussed. The first and second ionization potentials and electron affinities are calculated by the differences of the total energies between the ionized and nonionized systems and compared with the empirical inter-extrapolation results. The agreement between the present calculations and the inter-extrapolated results is excellent for the ionization potentials and reasonably good for the electron affinities of the quark atoms. Finally, the calculated ionization potentials and electron affinities are used in obtaining the electronegativities and hardnesses for these quark atoms.     

Electron propagator calculations of molecular electron affinities

An approximate electron propagator method for predictive calculations of molecular electron affinities is proposed. The self-energy accounts for relaxation effects to all orders Additional correlation effects are treated using a diagonal approximation with shifted denominators. Applications to CN, NH₂, and PH₂ are reported.     

On the evaluation of molecular electron affinities by approximate density functional theory

The ability of approximate Density Functional Theory to calculate molecular electron affinities has been probed by a series of calculations on the hydrides CH₃, NH₂, OH, and HC₂ as well as the multibonded species CN, BO, N₃, OCN, and NO₂. The simple Hartree–Fock Slater scheme lacks dynamic correlations and underestimates on the average the adiabatic electron affinities (EA_ad) by 0.7 eV. A considerable improvement is obtained by the Local Density Approximation (LDA) in which dynamic correlation is included. Values from LDA calculation underestimate, on the average, the adiabatic electron affinities by 0.4 eV. The best agreement with experiment is obtained by the LDA/NL scheme in which a nonlocal correction recently proposed by Becke is added to the LDA energy expression. The LDA/NL method underestimates EA_ad by 0.2 eV. It is concluded that the LDA/NL method affords EA_ad's in as good agreement with experiment as ab initio techniques in which electron correlation is taken into account by extensive configuration interaction. A full geometry optimization has been carried out on the nine neutral sample molecules as well as the corresponding anions.     

Theoretical calculations of proton affinities of azines. Prediction of the relative basicities and preferred protonation sites

Theoretical calculations at the 3-21G and 3-21 + G ab initio levels and at the MNDO and AM1 semiempirical levels of several six-membered nitrogenated heterocycles and their protonated species have been carried out. The 3–21G calculated proton affinities are systematically too high, in relation to the available experimental data, and it is estimated that inclusion of electron correlation and zero-point corrections is not sufficient to reach the desired agreement; however, additional inclusion of diffuse functions (3-21 + G/3-21G calculations) lowers the calculated proton affinities by 5.4–6.8 kcal/mol, a good agreement being thus obtained, at least for 1–7 . On the other hand, semiempirical methods underestimate the repulsion between each pair of vicinal nitrogens; however, if a correction of ?9 kcal/mol is added to the AM1 results for each pair of neighboring nitrogens containing lone pairs of electrons, the corresponding proton affinities match fairly well the available exoerimental data and corrected 3-21 + G results. As expected, all methods predict that the introduction of additional nitrogens decreases the overall absolute basicity. Futhermore, comparison of the relative basicity of the isomers and of the preferred protonation site for each isomer indicates that nitrogen atoms with (only) one α-nitrogen and without a γ-nitrogen are more basic than any others. In benzazines, MNDO and AM1 suggest that the 2,3-diaza arrangement has a higher intrinsic basicity than the 1,2-diaza arrangement.     

The estimation of electron affinities fromab initio 1s orbital energies

Summary It has been found that the electron affinities of alkoxy-radicals can be estimated using a correlation with the 1s orbital energy of the oxygen on the associated alkoxy-anion, EA=–0.64503 * (1s orbital energy) –351.58. The method assumes that the species of interest accepts the electron into an orbital which is localized on the oxygen.     

Radial subshell splittings and double-zeta functions in many-electron atoms

When the electron-electron interaction is explicitly considered in many-electron atoms, the average subshell radiusnl splits into two different radii, inner radius nl and outer radius >nl, where n and l are the principal and azimuthal quantum numbers. For the 102 atoms He through Lr in their ground states, the radii nl and nl are systematically examined at the Hartree-Fock limit level. For a subshell nl, two exponents zetanl(est) estimated from these radii have good linear correlations with variationally determined exponents zetanl(var) of double-zeta Slater-type functions.     

A semi-empirical MO theory for ionization potentials and electron affinities

A method for calculating the vertical ionization potentials and electron affinities according to their fundamental definition as differences between energies of the singlet ground and doublet ionized states is developed for cyclic hydrocarbons. The method adopts a new approach based on the central idea of a recent ab initio IP and EA calculation in which orbital exponents are optimized for both ground and ionized states. Hence, all the semi-empirical parameters of the MO theory are written as functions of the effective nuclear charge which, in turn, is made self-consistent with the molecular electronic charge distribution of the species. Although the MO theory is developed in the π electron approximation, the changes in the σ electron density, resulting from the loss or gain of a π electron, are explicitly considered in the calculation. The theory is compared to the earlier work of Hoyland and Goodman and tested against the first five polyacenes and on the condensed ring aromatics phenanthrene, pyrene, and perylene. Except for perylene, the results are in close agreement with the latest photoelectron spectroscopic measurements.     

Ionization potentials and electron affinities of carbo- and heterocyclicπ-conjugated molecules

The correlations of the observed ionization potentials and electron affinities with the orbital energies of SCF-MO's calculated by the variable- modification of the Pariser-Parr-Pople method were examined for 30 conjugated molecules including heterocycles. A simple linear relation has been found between the ionization potential and the energy of the highest occupied SCF-MO as well as between the electron affinity and the energy of the lowest vacant SCF-MO. The ionization potential and electron affinity are estimated by using these empirical relations for 24 conjugated heteromolecules of biochemical interest.

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Zusammenfassung PPP-Rechnungen nach der variables-Methode an 30 carbo- und heterocyclischen-Systemen zeigen eine gute Korrelation der experimentellen ionisationspotentiale und Elektronenaffinitäten mit den Energien der höchsten besetzten bzw. tiefsten unbesetzten SCF-MOs. Die so erhaltenen Regressionsgeraden wurden zur Bestimmung vos Ionisationspotentialen und Elektronenaffinitäten vos 24 biochemisch interessanten Heterosystemen herangezogen.

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Résumé Examen pour 30 molécules conjuguées des corrélations entre potentiels d'ionisation et affinités électroniques expérimentales avec les énergies des orbitales moléculaires SCF de la méthode de Pariser-Parr-Pople à variable. Une relation linéaire simple a été trouvée entre le potentiel d'ionisation et l'énergie de la plus haute orbitale moléculaire occupée ainsi qu'entre l'affinité électronique et l'énergie de la plus basse orbitale vacante. Ces relations empiriques permettent d'estimer les potentiels d'ionisation et l'affinité électronique de 24 molécules conjugées d'intérêt biochimique.