重要生物微量元素和常见负电性元素在不同价态和电子组态下的轨道指数和电负性

本文用Xα方法计算出不同价态与电子组态下锰、铁、钴、铜、锌及钼等过渡族重要生物微量元素和氮、氧、氟、磷、硫、氯、硒和溴等常见负电性元素的数值原子轨道和轨道电负性值,再用数值拟合方法得出这些原子轨道的单ξ和双ξSlater型基函数的指数.研究了这些元素的原子所带电荷和电子组态对其原子轨道指数与轨道电负性的影响,给出了相应的回归公式.这些公式有较高的精确度,不但为研究这些元素化合物的电子结构提供基础参数,也为电荷自洽型的计算提供较可靠的计算公式.     

重要生物微量元素和常见负电性元素在不同价态和电子组态下的轨道指数和电负性

本文用Xα方法计算出不同价态与电子组态下锰、铁、钴、铜、锌及钼等过渡族重要生物微量元素和氮、氧、氟、磷、硫、氯、硒和溴等常见负电性元素的数值原子轨道和轨道(?)负性值,再用数值拟合方法得出这些原子轨道的单ξ和双ξSlater型基函数的指数.研究了这些元素的原子所带电荷和电子组态对其原子轨道指数与轨道电负性的影响,给出了相应的回归公式.这些公式有较高的精确度,不但为研究这些元素化合物的电子结构提供基础参数,也为电荷自洽型的计算提供较可靠的计算公式.     

镧系元素4f轨道在成键中的作用的理论研究

用密度泛函方法在冻结或不冻结4f轨道的条件下计算一系列含镧系元素双原子 分子,对结果进行分析,得出以下结论：镧系元素4f轨道按传统的化学键理论观点 是不直接参与成键的,但对成键有一定作用：通过与匹配物的轨道混合使键长变短 ,键能增加,一般可达百分之几。随着镧系原子序数的增加4f轨道对成键的贡献减 少。电负性高或价态高的匹配物对4f轨道的作用较强,4f轨道对成键的影响比较大 。对于重镧系元素,匹配物不是F或O时,4f轨道对成键的贡献相当小,可以看成芯 轨道,但对于轻稀土,在比较精确的计算中则应作为价轨道处理。镧系元素与氟结 合时,只有对靠近Yb的重镧系元素才可以把4f当作芯轨道,而与氧结合时即使对于 YbO把Yb4f作为芯轨道仍会带来较大误差。     

电负性与原子价层轨道能

用密度泛函理论论证了原子价层轨道能与元素电负性之间的密切关系，说明如何用原子价层轨道能对元素电负性的概念进行解释，从而使周期表中元素电负性更容易被理解和计算。     

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。     

叠氮根电负性的量子化学研究

用ab initio, MINDO/3, MNDO和DV-Xa等量子化学方法计算研究了一些分子型和离子型(碱金属)叠氮化物及相应氯化物的平衡构型和电子结构。结构表明: 在分子型叠氮化物中叠氮根的电负性较氯小、与氮相当; 而在离子型金属叠氮化物中,叠氮根的电负性和氯相当或较氯稍大。将计算所得正则离域分子轨道进行定域化处理, 发现产生这种电负性差异的主要原因是上述两类叠氮化物中N2的成键状况不同, 本文对此进行了较为细致的分析。     

NMR偶合常数的从头算级别自然杂化轨道研究

为了研究自然杂化轨道计算结果与核自旋偶合常数的相关性,本文进行了从头算级别的自然杂化轨道计算。采用STO－3G基组,利用Lowdin正交化原子轨道基组下的密度矩阵,得到了分子中各原子的杂化轨道、净电荷与^13C-H、^13C-^13C键自旋偶合常数^1Jcn和^1Jcc之间关系式。利用这些式子计算得到的结果与实验数据非常一致。     

分子轨道成键性质及原子间化学键强度的成键能判据

本文定义了成键能Eb并用作分子轨道成键性质和分子中原子间化学键强度的判据。与Mulliken重叠布居Pb不同, 在成键能Eb中同时包含了原子轨道间的重叠因素和原子轨道的能量因素。对一些分子所作计算结果表明, 成键能判据较Mulliken重叠布居判据所得结论与实验更相符。     

镧系三氟化物的SCF-Xα-SW研究

对10个镧系元素(Ln)三氟化物进行了非相对论和相对论SCF-Xα-SW计算, 通过能级、轨道、结合能及布居数对比, 讨论化学键本质: 共价键中4f轨道的作用及相对论效应,结果表明, LnF3中Ln原子轨道参与成键的次序是: 轻稀土d>f>p>s, 而重稀土则有f>d>p>s。相对效应使Ln4f能级上移, 扩大了与F2p能级的距离, 减弱成键。原子序数增大, Ln4f能级下移, F2p能级距离缩小, 使重稀土氟化物中成键增强, 结合能计算值与实验值定性趋势一致, 重稀土氟化物电离能的计算表明, 相对论方案是获得定量符合所应该采用的。     

The Torsional Stability Around a Single Bond Analyzed by Extended Hückel Orbital Forces

A simple pencil and paper method to calculate the forces acting on individual atoms in a molecule, due to the electrons in the different populated molecular orbitals, has been developed within the Extended Hückel formalism. The method is applied to study the torsional stability around a single bond of some simple molecules. The results show good agreement with the experimental evidence of stable conformers.     

Orbital Correspondence Analysis in Maximum Symmetry

The use of Orbital Correspondence Analysis in Maximum Symmetry (OCAMS) for determining the allowed course of a reaction is described in terms of the familiar “A, S” notation. Several well known thermal and photochemical reactions are used as examples: Polyene cyclization; the fragmentation and dimerization of cyclobutadiene; [_π4 + _π2] cycloaddition; the isomerization of Dewar-benzene. The relation of OCAMS to the classical correlation procedures of Woodward and Hoffmann and of Longuet-Higgins and Abrahamson is brought out, as are the sources of the occasionally contradictory predictions of OCAMS and of the classical procedures.     

A Basis for Orbital Symmetry Rules

The influence of molecular symmetry on reaction rates is examined with an approach in which reactions are viewed as electronic transitions between states of reacants and products (described, in turn by quasiadiabatic potential surface). The moleculer Hamiltonian is used to derive selection rules for these transitions. The complete Hamilatonian has no useful symmetery. Neglect of non-Born-Oppenheimer and spin-orbit terms (and of other angular momentum coupling terms) leads to an apporixmate Hamiltonian and to selection rules which from the basis of the Woodward-Hoffmann rules. This apporch provides an alternative to the adiabatic potantial surfaces, reaction coordinates, and transition state theory used in more familiar discussions of the Woodward-Hoffmann rules. Further, it provides a particulary clear method for discussing violations of these symmetry rules, and for differentiating concerted and nonconcerted reactions.     

Extended Hückel Orbital Forces and the Jahn-Teller Distortions in Molecules

Linear orbital vibronic constants are calculated within the Extended Hückel formalism and used to evaluate the forces acting on the atoms along the symmetry coordinates, in a planar arrangement of four identical atoms. It is shown, from the magnitude and direction of the forces, that the high-symmetry square planar arrangement is unstable and distorts to lower symmetry.     

Orbital correspondence analysis in maximum symmetry: Formulation and conceptual framework

A recently proposed method for the analysis of the course of chemical reactions, based on the maximal use of available symmetry, is formulated as a set of procedural rules. The application of these rules is illustrated with a simple prototype reaction: CH₂+C₂H₄ fcyclo-C₃H₆. They are then derived, using the formalism of time-dependent perturbation theory within the Born-Oppenheimer approximation, thus bringing out the method's underlying assumptions and its relation to the widely used Woodward-Hoffmann procedure.     

A Homochiral Fulgide Organic Ferroelectric Crystal with Photoinduced Molecular Orbital Breaking

Thermally triggered spatial symmetry breaking in traditional ferroelectrics has been extensively studied for manipulation of the ferroelectricity. However, photoinduced molecular orbital breaking, which is promising for optical control of ferroelectric polarization, has been rarely explored. Herein, for the first time, we synthesized a homochiral fulgide organic ferroelectric crystal (E)-(R)-3-methyl-3-cyclohexylidene-4-(diphenylmethylene)dihydro-2,5-furandione ( 1 ), which exhibits both ferroelectricity and photoisomerization. Significantly, 1 shows a photoinduced reversible change in its molecular orbitals from the 3 π molecular orbitals in the open-ring isomer to 2 π and 1 σ molecular orbitals in the closed-ring isomer, which enables reversible ferroelectric domain switching by optical manipulation. To our knowledge, this is the first report revealing the manipulation of ferroelectric polarization in homochiral ferroelectric crystal by photoinduced breaking of molecular orbitals. This finding sheds light on the exploration of molecular orbital breaking in ferroelectrics for optical manipulation of ferroelectricity.     

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。     

环芳类化合物分子轨道相互作用的研究

建立模型分子描述环芳类分子中二苯环、二乙炔的π轨道间的相互作用,应用多重散主射Ｘα自洽场方法对模型分子的电子结构进行计算,得到分子轨道通过空间相互作用的大小随二苯环、二乙炔间距离的增加呈指数下降,在环芳类经合物分子电子结构研究基础上,分析了分子轨道通过键的相互作用,表明,分子轨道通过空间相互作用与通过键相互作用相互抵消,采用过滤态方法计算环芳类化合物分子前线分子轨道电离能,与实验符合较好。     

Frontier Molecular Orbital Engineering: Constructing Highly Efficient Narrowband Organic Electroluminescent Materials

It is of great strategic significance to develop highly efficient narrowband organic electroluminescent materials that can be utilized to manufacture ultra-high-definition (UHD) displays and meet or approach the requirements of Broadcast Television 2020 (B.T.2020) color gamut standards. This motif poses challenges for molecular design and synthesis, especially for developing generality, diversity, scalability, and robustness of molecular structures. The emergence of multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters has ingeniously solved the problems and demonstrated bright application prospects in the field of UHD displays, sparking a research boom. This Minireview summarizes the research endeavors of narrowband organic electroluminescent materials, with emphasis on the tremendous contribution of frontier molecular orbital engineering (FMOE) strategy. It combines the outstanding advantages of MR framework and donor-acceptor (D−A) structure, and can achieve red-shift and narrowband emission simultaneously, which is of great significance in the development of long-wavelength narrowband emitters with emission maxima especially exceeding 500 nm. We hope that this Minireview would provide some inspiration for what could transpire in the future.