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电负性是分子中一个原子把电子拉向它自身的能力,是化学理论的基本概念之一。继Pauling建立第一个电负性标度后,提出了众多的电负性标度。只是在密度泛函理论的基础上,电负性概念和电负性均衡原理,才被精密地论证。近二十多年来,电负性理论的重要发展是:应用电负性均衡模型或方法,可以快速地计算分子体系的电荷分布,从而确定分子的其他性质,甚至包括分子的结构和反应性指标。通常的电负性均衡方法只把分子划分到原子区域,虽然简单直观,但其精度和应用范围受到限制。原子与键电负性均衡方法,把分子划分到包括原子区域、化学键区域和孤对电子区域,能够较快速精密地计算分子的电荷分布和其他性质,并被应用到构建新一代可极化或浮动电荷力场的探索中,有广阔的应用前景。 相似文献
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The experimental approaches to estimation of comparative electronegativity and chemical hardness of organometallic groups have been proposed. Qualitative data on the electronegativity of L nM groups were obtained from 19F NMR study of model systems 4‐FC6H4QMLn (Q = CC, N(R), O, C(O)O, S), (4‐FC6H4)3 SnML n and (4‐FC6H4)3SnQML n (Q = O, S), containing a great variety of different organometallic groups containing transition or heavy main‐group metals. The data on chemical hardness of L nM groups were obtained from NMR study of distribution of different L nM groups between hard and soft anions. The following basic results have been obtained. (1) The relative electronegativity and chemical hardness of L nM groups can change in parallel or not with the electronegativity and hardness of the central metal atom. (2) The substituents in Ar can substantially modify electronegativity and hardness of Ar nM groups; the influence of Ar groups has an inductive nature; the increase in electron‐donating ability of aryl ligands enhances the hardness of Ar nM cations. (3) The relative electronegativity and hardness of L nM groups in L nMX are invariant and do not depend on X. 相似文献
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原子-键电负性均衡方法(ABEEM)是以密度泛函理论(DFT)和电负性均衡原理为基础发展而来,它明确地考虑了化学键是不引入任何实验数据的带纯理论性和计算的方法.使用统一标准并具有代表性和全面性地选择了200多个模型分子,利用可得到较准确结构的MP2/6-31G*优化结构,心/STO-3G单点计算得到Mulliken重叠布居,再用最小二乘法拟合得到许多主族元素在分子体系中的诸原子(包括单、双和叁键等不同成键状态)和化学键的ABEEM参数.所得到的原子的价态电负性可与已提出的其他电负性标度相比拟,计算CO得到的电荷负端为C(与从头计算的结果相反),结果与实验相符,且原子电荷的正负不完全由原子电负性决定. 相似文献
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The new ideas ofbond electronegativity andbond hardness are introduced, and a semiempirical density functional approach to the theory of molecular electronic structure and chemical binding is outlined. There result effective electronegativity equalization procedures that permit calculation of binding energies as well as partial charges. By a modelling of the bond electronegativity and bond hardness, a density functional interpretation of earlier bond charge models is established. Some numerical results are given for diatomic molecules.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday 相似文献
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The possible genesis of negative atom condensed Fukui functions is discussed based on hardness kernel matrix relationships. The recent hypothesis that diagonal dominance of the hardness matrix is a requirement for positive Fukui functions is proven, and general considerations also predict the possibility of regions with numerically unstable Fukui functions, including discontinuities. 相似文献
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By using a coarse-grain representation of the molecular electronic density, we demonstrate that the value of the condensed
Fukui function at an atomic site is directly related to the polarization charge (Coulomb hole) induced by a test electron
removed (or added) from (at) the atom. The link between the formation of an electron-hole pair and the condensed Fukui function
provides insights on the possible negativity of the Fukui function which is interpreted in terms of two phenomena: overscreening
and over-strengthening. 相似文献
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氢的电负性值是氢元素性质的重要参数,1932年Pauling犤1~3犦定量确定氢的相对电负性值等于2.1,1961年Allred犤4,5犦用更准确的实验数据对Paul-ing电负性标度进行了修正,氢的电负性值被确定为2.2,目前这两个数值都在采用。元素的电负性值是与元素的性质紧密相关的,一个合适的电负性标度应该至少反映所有重要元素的电负性值,氢的化合物比任何其它元素都多,理应有一个基本的准确电负性值,然而一些电负性标度中却缺乏这样的数据。在Murphy等四人犤6犦最近发表的论文中,对Pauling电负性标度又进行了深入考查与… 相似文献
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利用原子-键电负性均衡方法计算了700多个异构体的硬度, 通过与标准生成焓所确定的相对稳定性比较后发现, 多数异构体并不遵守最大硬度原理. 相似文献
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Through the application of the atom–bond electronegativity equalization method (ABEEM) to the calculation of the hardnesses of more than 300 tautomers, it can be seen that the maximum hardness principle is nearly useless to account for their relative stabilities. Moreover, by calculating the energies of these tautomers with the HF, B3LYP, B3PW91, and MP2 methods at the 6‐31G, 6‐31G*, 6‐31G**, 6‐31+G**, 6‐311G**, or 6‐311++G** level, it is found that all these methods may not be always reliable in predicting their relative stabilities. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
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Mihai V. Putz 《International journal of quantum chemistry》2006,106(2):361-389
A unified Mulliken valence with Parr ground‐state electronegativity picture is presented. It provides a useful analytical tool on which the absolute hardness as well ionization potential and electron affinity functionals are based. For all these chemical reactivity indices, systematic approximate density functionals are formulated within density functional softness theory and are applied to atomic systems. For the absolute hardness, a special relationship with the new electronegativity ansatz and a particular atomic trend paralleling the absolute electron affinity are established that should complement and augment the earlier finite‐difference energetic approach. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
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Esther Agacino Ricardo Gaitn Italo Menconi 《International journal of quantum chemistry》2006,106(8):1799-1808
An alternative way to calculate vertical ionization potentials (VIP) and vertical electron affinity (VEA) is the application of Koopman's theorem, using the electron propagator theory. In the present work, the results of the application of this theorem using the electron propagator formalism have been compared with the experiment in order to validate different basis set. Using the basis set with the best performance, the acidity tendencies in some substituted acetic acid molecules have been analyzed by correlating the proton affinity (PA) with molecular electronegativity (χ) and hardness (η); these last indexes were obtained from the calculated VIP and VEA considering the finite difference approximation. The above correlations were compared with equivalent correlations using the energy of the frontier Hartree–Fock orbitals and the corresponding Kohn–Sham orbitals, which were calculated with the B3LYP‐DFT procedure. The results indicate that the electron propagator theory could be an interesting alternative to evaluate reactivity indexes, since this theory gives reliable values of VIP and VEA. It was also found that (i) the VIP values are very close to experiment, with only a 0.38% of error; (ii) acceptable results are inferred for VEA; (iii) a triple zeta quality function works quite well in these calculations, and particularly the 6‐311G(d,p) basis set is the best, as it had been reported; and (iv) using the depronation energy (DPE), good results were obtained in the correlations δDPE‐VEA and δDPE‐χ. The results tested that P3 approximation in the electron propagator approach can be a new and interesting alternative in predicting VIP, VEA, and some reactivity indexes, such as χ and η, at least for the compounds studied. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献