ABn的节面、分子轨道和能级

考虑到重叠轨道间交角的影响，可将Ｈｅｉｌｂｒｏｎｎｅｒ定性ＨＭＯ理论成功地推广到ＡＢ_ｎ体系。得出了分子轨道中轨道间重叠和节面的分布情况。结果表明原子轨道间的成键作用，以成键和反键二极分化最大为原则。有８ｎ个价电子的ＡＢ_ｎ呈高对称性构型；８ｎ＋２个价电子的ＡＢ_ｎ则呈低对称性构型。     

精确的甲烷分子价轨道的电子动量谱学研究

电子动量谱学（EMS）已发展成为探测原子分子电子结构的强有力工具．借助电子动量谱学可获得精确的分子轨道电子密度分布，并能提供非常详细的电子运动和电子关联信息．分子电子密度分布和电子运动的详细了解对分子的识别和化学活性的理解非常重要，并且也有助于计算机辅助的分     

反键分子轨道与对称性关系

根据群论，阐述了对称性匹配的原子轨道不仅可以组成成键分子轨道，同样可组成反键分子轨道，否定了反键分子轨道是由对称性不匹配原子轨道组合的观点     

计算化学在分子轨道教学中的应用

分子轨道理论是理解分子电子结构与微观性质的重要理论之一,也是本科生与研究生结构化学教学中的重点与难点。学生对原子轨道组合形成分子轨道、分子轨道能级交叉混合等知识的理解缺乏形象直观、定量的认识。本文通过基于量子化学或密度泛函理论的Gaussian 03计算软件,计算、绘制并分析了F_2、O_2、N_2、HF、CO等的分子轨道能级图,将学生较难理解的内容定量、直观地呈现出来,形象地解释了分子轨道成键原则与电子填充原则等分子轨道理论中的重难点,加深了学生对分子轨道理论的理解,特别是sp轨道混杂导致的σ_(2p_z)与π_(2p)轨道能级交叉这一难点,激发了学生学习的主动性和积极性,提高了教学质量。在此基础上,利用分子轨道理论分析了CO_2的电子结构,使学生学会应用分子轨道理论解决实际问题,巩固了相关课堂理论知识。     

分子轨道的投影方法

本文根据Mollweide投影讨论MX_n分子和M_n簇骨架的分子轨道的平面投影表示方法,定性描述分子轨道的成键特性.     

Hickel分子轨道计算的割键法则及其应用

Tang Ao-qing et al. have put forward graph theory method for determining the Huckel molecular orbits and the calculation of energy levels for conjugated molecules. Based on the work of the forerunners, the bond-break rule for determining the molecular orbits is presented in this paper. The general concept of the bond ratio is first introduced. The calculation of orbital coefficients and of energy levels are transformed into a calculation of bond ratio and of energy levels. Following the rules governing bond-breaking established in this paper to break some bonds in the structural diagram of molecules and at the same time modify the Coulomb's integration of atoms, it becomes possible to use a group of mutually independent sub-diagrams to replace the complicated structural diagram of molecules. The secular determinants of each sub-diagram must all equal zero. Thereby series of equations (called series of equations of bond ratio) can be established with the energy level and the bond ratio as the unkowns. When this is solved, the energy level and bond ratio are obtained. Because of the simplicity of the construction of the sub-diagrams, the calculation is greatly simplified when this method is used. Futhermore, this method can be widely applied to all kinds of complicated conjugated molecules. In this paper the authors have gone through some calculations for molecules with heteropoly-radicals.     

分子轨道计算应用于核化学与同位素化学

随着量子化学计算技术的发展,用量子化学来定量地处理和解决科学问题的对象愈加广泛。本文简单地介绍了分子轨道(简称MO,下同)计算应用于核化学、放射化学和同位素化学,诸如对萃取剂性能的理论分析、放射核素衰变对分子稳定性的影响、同位素效应的计算和在核药物化学中的应用。     

轨道和波函数

分子（或原子）轨道是化学的基本概念之一。本文从Bohr原子轨道入手,介绍轨道概念的演化,以及轨道与波函数之间的关系,分子轨道与原子轨道之间的关系,并结合量化计算介绍基组与分子轨道的关系。     

有机链状分子的定域分子轨道的研究

利用Foster-Boys定域化程序和STO-3G ab initio方法,对含有C、H、O、N原子的100多个有机链状分子进行了研究,得到定域分子轨道能量及其相互作用参数。应用这些参数和定域分子轨道模型,对于众多的含有C、H、O、N原子的有机链状分子,可得到相应的正则分子轨道能量及其与定域分子轨道的关系。以此预测它们的电离能,结果与实验值符合较好。     

定域分子轨道对称性

提出了利用定域分子轨道重心确定分子轨道的对称性。确定了线型的、非线型的、环状的分子定域分子轨道对称性。结果表明非线型分子和其中双中心键具有相同对称性,但含孤对或三中心键的分子则存在一些差别。还讨论了定域分子轨道的特征。     

原子轨道的函数表示及可视化

量子化学中,Gaussian型函数是常用的一种基组函数。但最初原子核外单电子波函数的解析解是Slater型函数。介绍了2者之间的差异,以及Gaussian型函数被广泛采用的原因。在介绍这些概念的同时,作者将所涉及的函数形式使用免费的绘图软件gnuplot进行可视化,并给出相应代码,以助于学生更好地理解物理概念以及抽象的数学形式。     

Maximum Overlap Symmetry Molecular Orbital Calculation under CNDO／2 Approximation

ＭａｘｉｍｕｍＯｖｅｒｌａｐＳｙｍｍｅｔｒｙＭｏｌｅｃｕｌａｒＯｒｂｉｔａｌＣａｌｃｕｌａｔｉｏｎｕｎｄｅｒＣＮＤＯ／２ＡｐｐｒｏｘｉｍａｔｉｏｎＹｅＳｈｉ－Ｙｏｎｇ；ＺｈａｎＣｈａｎｇ－Ｇｕｏ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，Ｃｅｎｔｒ...     

Linear Approximation of Basis Set Orbital Exponents for Isoelectronic Series of Atoms

The orbital exponents of Slater type atomic orbitals (AOs) in isoelectronic series of atoms may be approximated by the linear dependence on the nuclear charge using a technique developed for optimization of AO basis sets in Hartree–Fock–Roothaan calculations. This approach yields the analytical Hartree–Fock wave functions for any ion in the isoelectronic atomic series without optimization of orbital exponents. The approximated linear equations for atomic orbital basis sets of B, C, O, and F in the ground state are presented as an example.     

Orbital connections for perturbation-dependent basis sets

Summary The use of perturbation-dependent basis sets is analysed with emphasis on the connection between the basis sets at different values of the perturbation strength. A particular connection, the natural connection, that minimizes the change of the basis set orbitals is devised and the second quantization realization of this connection is introduced. It is shown that the natural connection is important for the efficient evaluation of molecular properties and for the physical interpretation of the terms entering the calculated properties. For example, in molecular Hessian calculations the natural connection reduces the size of the relaxation term, leading to faster convergence of the response equations. The physical separation of the terms also means that first-order non-adiabatic coupling matrix elements can be obtained in a very simple way from a molecular Hessian calculation.     

Crystal Structure and Molecular Orbital Calculation of（1R，2S）－N－Methylephedine Benzoate Hydrochloride

ＣｒｙｓｔａｌＳｔｒｕｃｔｕｒｅａｎｄＭｏｌｅｃｕｌａｒＯｒｂｉｔａｌＣａｌｃｕｌａｔｉｏｎｏｆ（１Ｒ，２Ｓ）－Ｎ－ＭｅｔｈｙｌｅｐｈｅｄｉｎｅＢｅｎｚｏａｔｅＨｙｄｒｏｃｈｌｏｒｉｄｅＣｈｅｎｇＸｉａｏ－Ｊｕｎ（ＥｎｖｉｒｏｎｍｅｎｔａｌＰｒｏｔｅ...     

Frontier Orbital Control of Molecular Conductance and its Switching

For transmission of electrons through a π system, when the Landauer theory of molecular conductance is viewed from a molecular orbital (MO) perspective, there obtains a simple perturbation theoretic dependence, due to Yoshizawa and Tada, on a) the product of the orbital coefficients at the sites of electrode attachment, and b) the MO energies. The frontier orbitals consistently and simply indicate high or low transmission, even if other orbitals may contribute. This formalism, with its consequent reinforcement and/or interference of conductance, accounts for the (previously explained) difference in direct vs. cross conjugated transmission across an ethylene, as well as the comparative ON/OFF ratios in the experimentally investigated dimethyldihydropyrene and dithienylethene‐type single‐molecule switches. A strong dependence of the conductance on the site of attachment of the electrodes in a π system is an immediate extrapolation; the theory then predicts that for some specified sites the switching behavior will be inverted; i.e. the “open” molecular form of the switch will be more conductive.     

Basis Set Orbital Relaxation in Atomic and Molecular Hydrogen Systems

Orbital relaxation (OR) amounts to variation of the orbital exponents in hydrogen molecules and ions relative to the exponents of the isolated atom; it is represented as the sum of the one- and two-center contributions depending on the effective atomic charge and on the presence of other atoms in the molecule. The procedure for isolating the contributions of the exponent includes treatment of the OR of hydrogen in a special set of neutral and charged atoms and molecules with certain multiplicities of their electronic states. Within the framework of the spin-unrestricted Hartree-Fock method, we found and discussed the optimal values of the exponents of the basis orbitals of hydrogen atoms and molecules using the minimal split valence-shell basis set, the basis set that includes the polarization function, and the expanded set of grouped natural orbitals. A simple energy model is suggested for OR. Expressions are derived for evaluating the exponents of the relaxed orbitals in hydrogen-containing systems.Original Russian Text Copyright © 2004 by A. I. Ermakov, A. E. Merkulov, A. A. Svechnikova, and V. V. Belousov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 973–978, November–December, 2004.     

双核钼硫原子簇顺反异构体的定域化分子轨道研究

本文对簇合物离子[Mo_2(μ-S)_2S_2(S_2C_2H_4))_2]~(2-)的顺式和反式异构体进行了CNDO定域化计算,讨论了它的两种异构体的化学键性质,特别是Mo—Y(S)间的三重键性质.探讨了用亚层Mulliken布居数分析键的性质的可能性,并说明了这类簇离子多以顺式异构体存在的原因.     

Orbital Energy Order and the Through Bond Interaction in Homonuclear Diatomic Molecules

The homonuclear diatomic molecules are the simplest systems having both the σ framework and the lone pair orbitals n_a and _b for investigating their through space and through bond interaction. The striking orbital energy order n_g～ n_a+ n_b > n_n ～ n_a - n_b has been accounted for by the through bond interaction. However, when the p-content in the lone pair orbitals n_a and n_b decreases, one may have the reverse orbital energy order: n_g < n_g. A reverse orbital energy order has been found in F₂ and Cl₂, whose n_a and n_b are almost pure s-type atomic orbitals. The reverse order also occurs in molecule N₂ when the internuclear distance is larger man 1.5 Å. It is also found that the detail through space and through bond interaction and the eventual orbital energy order for n_g and n_u can be accounted for by the Fock operator within the localized molecular orbital space.     

自然定域轨道方法研究

本文报导我们按自然定域轨道原理编制的NLMO程序以及对自然定域轨道计算方法的一些改进。用NLMO程序计算出七个具有不同成键特性分子(包括是否含有孤对或π键,是否含有多中心键等不同情况)的自然定域轨道,结果与用其它定域化方法得出的基本一致。由于自然定域轨道方法基本上具有内禀定域性质,而计算量明显小于其它定域化方法,可以认为它是有效和方便的。