CNDO/2法的碎片价轨道近似 Ⅰ. 原理

本文提出一种简化的处理方法, 在研究桥联原子簇化合物电子结构时把端基看成碎片, 取碎片的部分价轨道参与整个分子的计算以节约机时, 在CND0/2法基础上推导出碎片价轨道近似法的公式, 并用FORTRAN语言编写程序, 在PDP-11-70机上实现。本法可望用于较大分子体系的局部几何构型优化及反应机理等计算量较大的研究。     

Ligand-derived oxidase activity. Catalytic aerial oxidation of alcohols (including methanol) by Cu(II)-diradical complexes

Seven new bis(o-iminosemiquinonato)copper(II) complexes, 1- 5, 1a, 1b, derived from differently substituted N-phenyl-2-aminophenol-based ligands, are described. Their crystal structures were determined by X-ray diffraction, and their electronic structures were established by various physical methods including electron paramagnetic resonance and variable-temperature (2-290 K) susceptibility measurements. Like complex 6, which was reported recently by us, all complexes exhibit an S t = (1)/ 2 ground state, based on the "isolated" copper(II)-spin character resulting from the dominating antiferromagnetic spin coupling between the two radicals; the ground-state electronic configuration can thus be designated as (increasing, increasing, decreasing)[R-Cu-R]. In addition, broken spin symmetry density functional solutions have been obtained. From the set of unrestricted canonical Kohn-Sham orbitals, the magnetic orbitals have been identified. The identification procedure is based on the nonvanishing overlap integrals between the space parts of orbitals occupied by electrons of opposite spin. The theoretically determined magnetic orbitals support the spin configurations suggested by the experiments. Electrochemical measurements (cyclic voltammetry and square-wave voltammetry) indicate ligand-centered redox processes. Complex 1 is found to be the best catalyst among the Cu(II) complexes for oxidation of primary alcohols with aerial oxygen as the sole oxidant to afford aldehydes under mild conditions. Thus, the function of the copper-containing enzyme Galactose Oxidase has been mimicked. Kinetic measurements in conjunction with electron paramagnetic resonance and electronic spectral studies have been used to decipher the catalytic oxidation process. A ligand-derived redox activity has been proposed as a mechanism for the aerial oxidation of primary alcohols.     

Optimal virtual orbitals to relax wave functions built up with transferred extremely localized molecular orbitals

Extremely localized molecular orbitals (ELMOs), namely orbitals strictly localized on molecular fragments, are easily transferable from one molecule to another one. Hence, they provide a natural way to set up the electronic structure of large molecules using a data base of orbitals obtained from model molecules. However, this procedure obviously increases the energy with respect to a traditional MO calculation. To gain accuracy, it is important to introduce a partial electron delocalization. This can be carried out by defining proper optimal virtual orbitals that supply an efficient set for nonorthogonal configurations to be employed in VB-like expansions.     

Multielectron coincidence spectroscopy for core-valence doubly ionized states of CO

Double photoionization into states which have holes in one core and one valence orbitals has been observed in CO using a state-of-the-art multielectron coincidence method. The core-valence CO2+ structures exhibited on the electron coincidence spectra are assigned by comparison with the available calculation [H. Schulte et al., J. Chem. Phys. 105, 11108 (1996)]. Features of the spectrum confirm that the properties of the CO2+ states are characterized by the interaction between the localized valence holes and the core holes.     

可见光响应光催化剂K4Ce2Ta10O30、K4Ce2Nb10O30及其固溶体的电子结构

基于密度泛函理论(DFT), 采用平面波赝势(PWP)以及广义梯度近似(GGA)方法, 对可见光响应的光催化剂K4Ce2Ta10O30、K4Ce2Nb10O30及其固溶体进行电子结构的第一性原理计算. 结果表明, 光催化剂K4Ce2Ta10O30和K4Ce2Nb10O30的导带分别主要由Ta 5d和Nb 4d组成, 处于高能级的电子未占据态的Ce 4f与其有很明显的重迭, 但由于其高度局域特性,不能很好地参与光生电子在导带中的传导, 从而对光催化活性的贡献很小;而其价带则由O 2p与Ta 5d (Nb 4d)的杂化轨道组成, 同时电子占据态的Ce 4f对价带也有一定的贡献, 各个电子轨道对能带结构的贡献决定了该系列可见光响应光催化剂的物理化学和光催化特性. 固溶体系列中随着Nb含量的增加, 其吸收光谱依次红移, 带隙变窄, 导带底变低, 光生电子的还原能力降低. 在固溶体K4Ce2Ta10-xNbxO30(x=2, 5, 8)中, 由于Ce 4f轨道对价带顶的贡献相对较小, 固溶体的价带顶低于K4Ce2Ta10O30、K4Ce2Nb10O30的价带顶, 光生空穴的氧化能力相对较强. 该系列光催化剂的电子结构分析结果与光催化水分解的活性实验结果有很好的一致性.     

六核簇离子Te64+和P64-的电子结构与化学键

本文用EHMO法计算六核簇离子Te₆⁴⁺和P₆^4-的电子结构。分析与它们相同构型的棱柱烷C₆H₆和苯在成键性质上的差异。结果表明,这两簇离子的多余价电子填充到能级略高于自由原子p轨道的弱反键分子轨道。     

Molecular orbital calculations based on linear combinations of fragment orbitals

A semiempirical MO method based on localized fragment orbitals has been developed, which is particularly suited for the construction of orbital correlation diagrams for the discussion of the electronic structure of complex molecules in terms of fragments and their interactions. The method allows for the inclusion of experimental ionization potentials and electron affinities of the fragments within the calculation of the Fock matrix elements and may thus form the basis of an interpretation of photoelectron spectra, comparable to the interpretation of UV spectra by means of the MIM method of Longuet-Higgins and Murrell. Several levels of approximation are discussed using the acrolein molecule as an example.     

Aromaticity and electronic delocalization in all-metal clusters with single, double, and triple aromatic character

A series of monocyclic planar inorganic compounds with single, double, and triple (anti)aromatic character has been studied. The electron delocalization and aromaticity of these compounds have been assessed by means of two-center and multicenter electronic delocalization indices and their ??-, ??-, and ??-components. Results show that these indices are excellent predictors of the ??-, ??-, and ??-aromatic character of all-metal and semimetal clusters.     

Structure and packing arrangement of molecular compounds

The calculation of electronic structures of TCNQ and several electron-donor molecules has been performed by the Iterative Extended Hückel Method, taking into account all valence electrons of various atoms and retaining the overlap integrals. Calculations of intermolecular overlaps involving the lowest vacant molecular orbital of TCNQ and one or more highest occupied orbitals of each of the donors have been correlated with the observed donor-TCNQ geometrical configurations. The results of this simple approach, which is based on Mulliken's “Overlap and Orientation Principle”, suggest that the charge-transfer interaction plays an important role in the particular observed packing arrangement in the solid state.     

Comparative Investigation of QHS and DQHS with Density Functional Theory

1 INTRODUCTION QHS (C15H22O5) is a novel antimalarial drug isolated from Chinese herb Artemisia annua L in 1972. Structural studies by chemical analysis, X-ray single-crystal diffraction and other spectroscopic me- thods showed that QHS is a sesquiterpene lactone with a peroxide group (Fig. 1)[1]. In the past few decades, great achievements have been acquired in search for the mechanism of action of QHS[2～5]. Its unique endoperoxy bridge has attracted worldwide attention. Due to …     

Localization of molecular orbitals on fragments

A non‐iterative algorithm for the localization of molecular orbitals (MOs) from complete active space self consistent field (CASSCF) and for single‐determinantal wave functions on predefined moieties is given. The localized fragment orbitals can be used to analyze chemical reactions between fragments and also the binding of fragments in the product molecule with a fragments‐in‐molecules approach by using a valence bond expansion of the CASSCF wave function. The algorithm is an example of the orthogonal Procrustes problem, which is a matrix optimization problem using the singular value decomposition. It is based on the similarity of the set of MOs for the moieties to the localized MOs of the molecule; the similarity is expressed by overlap matrices between the original fragment MOs and the localized MOs. For CASSCF wave functions, localization is done independently in the space of occupied orbitals and active orbitals, whereas, the space of virtual orbitals is mostly uninteresting. Localization of Hartree–Fock or Kohn–Sham density functional theory orbitals is not straightforward; rather, it needs careful consideration, because in this case some virtual orbitals are needed but the space of virtual orbitals depends on the basis sets used and causes considerable problems due to the diffuse character of most virtual orbitals. © 2012 Wiley Periodicals, Inc.     

Local Hartree–Fock orbitals using a three‐level optimization strategy for the energy

Using the three‐level energy optimization procedure combined with a refined version of the least‐change strategy for the orbitals—where an explicit localization is performed at the valence basis level—it is shown how to more efficiently determine a set of local Hartree–Fock orbitals. Further, a core–valence separation of the least‐change occupied orbital space is introduced. Numerical results comparing valence basis localized orbitals and canonical molecular orbitals as starting guesses for the full basis localization are presented. The results show that the localization of the occupied orbitals may be performed at a small computational cost if valence basis localized orbitals are used as a starting guess. For the unoccupied space, about half the number of iterations are required if valence localized orbitals are used as a starting guess compared to a canonical set of unoccupied Hartree–Fock orbitals. Different local minima may be obtained when different starting guesses are used. However, the different minima all correspond to orbitals with approximately the same locality. © 2013 Wiley Periodicals, Inc.     

LiPN<Subscript>2</Subscript> and NaPN<Subscript>2</Subscript> crystals: Structural features and chemical bonding

The band structure spectra, densities of states, and valence and difference densities of LiPN₂ and NaPN₂ crystals were obtained by DFT self-consistent calculations using the nonlocal pseudopotentials and the localized pseudoorbital basis. Crystal-chemical analysis of these compounds shows that they occupy an intermediate position between the ideal structures of β-cristobalite and chalcopyrite, which manifests itself in the peculiarities of the electronic structure and chemical bonding. The valence band consists of three allowed subbands and differs radically from the typical valence band of chalcopyrite crystals in both subband structure and contributions of the s, p, and d atomic orbitals to the crystal orbitals.     

On the Quantum Chemical Nature of Lead(II) “Lone Pair”

We study the quantum chemical nature of the Lead(II) valence basins, sometimes called the lead “lone pair”. Using various chemical interpretation tools, such as molecular orbital analysis, natural bond orbitals (NBO), natural population analysis (NPA) and electron localization function (ELF) topological analysis, we study a variety of Lead(II) complexes. A careful analysis of the results shows that the optimal structures of the lead complexes are only governed by the 6s and 6p subshells, whereas no involvement of the 5d orbitals is found. Similarly, we do not find any significant contribution of the 6d. Therefore, the Pb(II) complexation with its ligand can be explained through the interaction of the 6s² electrons and the accepting 6p orbitals. We detail the potential structural and dynamical consequences of such electronic structure organization of the Pb (II) valence domain.     

Computational developments in generalized valence bond calculations

In this article a procedure for generating starting orbitals for generalized valence bond (GVB) calculations is presented. This is achieved by selecting orbitals which correspond to specific bonds or electron pairs. These orbitals can be identified from the localized molecular orbitals, for both occupied and virtual orbitals, which are obtained through a unitary transformation of the Hartree-Fock canonical molecular orbitals using the Boys's localization method. A scheme has also been implemented which achieves optimum convergence of the pairwise orbital optimization. An object-oriented GVB program is developed which automatically generates reliable initial GVB orbitals, leading to proper and fast convergence. © 1996 by John Wiley & Sons, Inc.     

Coherent superposition of resonance wave function in terms of weighted orthogonalized natural localized configurations

In this research, the projection technique has been applied in order to decompose the electronic wave function into its weighted orthogonalized resonance components. These components have been constructed by determinants whose orbitals are selected among natural bond orbitals. However, the procedure is general and any other localized orbitals can be used as well. Both σ and π delocalize systems have been considered in order to check the reliability of the calculated resonance weights. For π‐systems, the presented procedure could predict significant decrease of weight of certain resonance structures when the molecular planarity was destroyed. Water cyclic clusters were also tested and the results confirmed the existence of strong σ‐delocalization in the clusters. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008