Systematic formulations for electronegativity and hardness and their atomic scales within density functional softness theory

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     

Semiempirical calculation of electronic spectra of organic compounds by using the improved method of new-γ electron repulsion integral. Part 2. Polycyclic aromatic hydrocarbons (PAHs)

Excitation energies of 123 polycyclic aromatic hydrocarbons were calculated by incorporating the improved method of new-γ for the two-center electron repulsion integral into two semiempirical molecular orbital methods (CNDO/S and INDO/S). This variable method well reproduced experimental excitation energies of them. The average error of the improvement is about 0.162 (CNDO/S) or 0.237 eV (INDO/S) though the average error without the improvement is about 0.541 (CNDO/S) or 0.536 eV (INDO/S). The improvement was useful for the calculations of other organic compounds including hetero atoms, such as organic dye.     

Probing the hydride transfer process in the lumiflavine-1-methylnicotinamide model system using group softness

The hydride transfer process between the isoalloxazine moiety of flavins and the nicotinamide moiety of NAD(P)H has been explored by using density functional theory based reactivity index in the 1-methylnicotinamide-lumiflavine model system. Based on crystallographic data available, we have found that the group softness index helps to locate and orientate reactive regions in these interacting molecules while the electrophilicity index successfully describes the reactivity pattern of this system.     

Structures and hardness of ethyl halides and ethyl tosylate

Ab initio calculations (RHF) of EtX molecules (X=F, Cl, Br, I, or OTs) were carried out with the use of different basis sets. Total charges on the atoms in the compounds under study were determined by Mulliken's, NPA, and Bader's methods, and a comparison of these values was performed. For all EtX compounds, a topological analysis of the electron density was carried out within the framework of Bader's theory, and the global and relative local hardnesses of the above-mentioned ethylating agents were estimated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 608–612, April, 1998.     

利用ABEEMσπ模型研究哺乳类催产素及其衍生物

哺乳类催产素及其衍生物是一系列包含S—S键的多肽分子. 应用原子-键电负性均衡σπ(ABEEMσπ)模型, 我们研究了该系列多肽分子的分子内氢键和整体软度与生物活性关系. 首先利用点电荷模型计算了该系列多肽分子的分子内氢键能, 并与实验值对比, 得到了基本一致的结果. 再根据整体软度与生物活性的关系: 即整体软度越大, 分子生物活性越大, 我们成功解释了催产素及其衍生物的分子生物活性的变化关系. 将ABEEMσπ模型初步应用于研究含 S—S键多肽的相关性质方面, 并取得了和实验以及其它理论计算较为一致的结果. 因此, 以上研究为该模型进一步探讨其它多肽的相关性质提供了一定的理论基础.     

Understanding Chemical Reactivity in Extended Systems:Exploring Models of Chemical Softness in Carbon Nanotubes

Chemical reactivity towards electron transfer is captured by the Fukui function.However,this is not well defined when the system or its ions have degenerate or pseudo-degenerate ground states.In such a case,the first-order chemical response is not independent of the perturbation and the correct response has to be computed using the mathematical formalism of perturbation theory for degenerate states.Spatialpseudo-degeneracy is ubiquitous in nanostructures with high symmetry and totally extended systems.Given the size of these systems,using degenerate-state perturbation theory is impractical because it requires the calculation of many excited states.Here we present an alternative to compute the chemical response of extended systems using models of local softness in terms of the local density of states.The local softness is approximately equal to the density of states at the Fermi level.However,such approximation leaves out the contribution of inner states.In order to include and weight the contribution of the states around the Fermi level,a model inspired by the long-range behavior of the local softness is presented.Single wall capped carbon nanotubes(SWCCNT) illustrate the limitation of the frontier orbital theory in extended systems.Thus,we have used a C360 SWCCNT to test the proposed model and how it compares with available models based on the local density of states.Interestingly,a simple Hü ckel approximation captures the main features of chemical response of these systems.Our results suggest that density-of-states models of the softness along simple tight binding Hamiltonians could be used to explore the chemical reactivity of more complex system,such a surfaces and nanoparticles.     

Theoretical investigation of the stereoselectivity of some Diels-Alder reactions involving cyclopentadiene

The stereoselectivity of some Diels-Alder reactions was investigated by means of ABEEM-oTr model.Combined with local hard-soft and acid-base(HSAB)principle,we made reasonable explanation by calculating local softness of atom and bond regions for the stereoselectivity of four Diels-Alder reactions involving cyclopentadiene.     

电负性均衡

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。