三原子分子振转激发态的理论研究

三原子分子振转激发态的理论研究谢代前,鄢国森,田安民（四川大学化学系,成都,６１００６４）关键词振转激发态,三原子分子,变分法能级较高的振转激发态通常包含大振幅运动,其波函数分布于很广的势能面区域内,传统的正则模理论已不适合于解决这类问题．近年来,Ｈ...     

用分子子图法计算硝基呋咱化合物的生成热

用新的分子子图法计算硝基呋咱类化合物的生成热,将呋咱基团视为母体,即基子图项;硝基、叠氮基、甲基、氰基拆分为一个个原子,从原子的角度来分分子子图,将碳、氢、氧、氮原子视为取代基,即亚子图项.同时考虑呋咱基团的个数,考虑1位、 2位、 3位、 4位上碳、氢、氧、氮原子及双键、叁键对生成热的影响,还考虑不饱和度、总硝基个数、环的个数(除呋咱环)、氮氮及氮氧双键的个数对生成热的影响.用这种新的分子子图编码方法,对硝基呋咱化合物的生成热进行了拟合和预估,取得了满意的结果,其回归方程的相关系数达到了0.9954.     

三原子共价分子的几何构型

一三原子共价分子的几何构型,经实验测定,不外乎是分属线型及V型两种不同类型。对主族元素所构成的分子,一般用以解释     

反向分子设计方面涌现的新方法

在化学,物理,生物和材料科学中,分子设计是必不可少且无处不在的．然而,由极多候选分子组成的巨大空间需要新颖的优化方法去搜索,以便实现高效的分子设计．本文首先总结了分子设计领域内已发展成熟的优化算法,比如穷举算法、分支定界算法、蒙特卡罗类似算法及基因算法．通过若干有代表性的分子设计实例,我们介绍了上述算法的具体应用．其次,本文主要侧重于介绍最新发展的反向分子设计的策略,比如反向能带结构优化算法以及线性展开原子势场方法,并且对后者展开了详细阐述．线性展开原子势场方法选择了核电吸引势场做为优化变量,因为每个中性分子包含的原子类型和原子的空间位置均由此势场决定．本质上,核电吸引势场决定了分子以及分子的所有化学和物理性质．但是核电吸引势场本身不是一个任意的势场,它必须包含合理的分子结构信息．因此,此势场由原子的或者功能团的核电吸引势场做线性展开．通过优化线性展开系数,所感兴趣的分子性质得以最大化或者最小化,同时每个原子的或者功能团所对应的系数包含了最终分子的组成信息．基于密度泛函理论和一个简单的分子模型,我们成功地应用线性展开原子势场方法优化了分子的超极化率．然而,当所感兴趣的分子性质变得复杂或者线性展开中的功能团变得多样化,分子性质曲面也会包含更多的局部最优值．为了有效地搜索复杂的分子性质曲面,我们发展了梯度引导的蒙特卡罗算法．经典的蒙特卡罗算法每次随机地产生新的分子,而梯度引导的蒙特卡罗利用上述方法构造的分子性质曲面,首先计算当前分子所在处的局部梯度相对于所有官能团的展开系数,然后基于此梯度产生下一个分子,最后利用Metropolis规则接受或者拒绝新产生的分子．换句话说,梯度引导的蒙特卡罗算法是一个“半随机”的算法．我们首先应用梯度引导的蒙特卡罗算法,结合线性展开原子势场方法计算的局部梯度,优化了带有普林环的分子框架的超极化率．此外,对于任何一个可构造出分子性质曲面的全局优化问题,梯度引导的蒙特卡罗算法均可适用．比如,我们应用此算法优化了蛋白质的氨基酸序列并探讨了蛋白质的折叠问题．这些具体的应用实例证明了梯度引导的蒙特卡罗算法能够有效地搜索分子空间,根据所感兴趣的分子性质,筛选出最优的分子．总之,本文综述了反向设计的方法近况及其基本原理,将有助于促进分子设计的进程．     

四原子分子中Majorana算子矩阵元的新计算公式

李代数方法在研究双原子分子、三原子分子振－转光谱及相关问题等方面已被证明是一种有效方法[‘－0,并被成功推广到多原子分子[’－门．构造代数哈密顿量是此方法的关键,这就要求选择合适的     

OCS分子单重态和三重态结构的密度泛函理论研究

OCS是大气同温层中唯一的硫化物，与CS2、N2O和CO2等一样都是具有16个价电子的闭壳层分子，这些典型三原子分子的电子结构与性质一直为理论和实验工作者所关注。尽管它们只是简单的三原子分子，但仍有一些性质不为人所知。目前还未见有关OCS分子电子结构与性质的研究报道。     

原子结构和元素周期律

在化学教学中的亲身经验和观察,使我们相信,学习了门捷列夫元素周期律和元素周期表、原子结构以后,十年级的学生能毫无困难地绘出短周期元素的原子结构图,按元素在周期表中的位置来决定其电子层和价电子数,说明原子量具有小数的原因,即是充分地、清楚地弄懂了周期表的物理意义。但是,这个观念大部分带有统计学的特征。学生不仅要知道周期和族里的元素性质发生的变化,而且要知道为什么发生这些变化。     

四原子分子振转相互作用的Lie代数方法

利用Lie代数方法研究了四原子分子振转相互作用，在代数框架内首次给出四 原子分子振转相互作用的张量算子非对角矩阵元的表达式，利用这些表达式对线型 四原子分子HCCF振转相互作用的l-doubling进行了计算。     

确定三原子分子势能面的SCF-CI方法

建议根据振动高激发态的实验能级确定三原子分子势能面的SCF-CI方法.此法中使用键长-键角内坐标系下的SCF-CI方法来精确地计算振动高激发态的能级及其对势能参数的一阶微分,并使用LMF算法来优化势能参数.为验证此方法,优化了水分子的势能面,计算出水分子的振动高激发态能级与70个观测到的振动能级相比较,标准偏差为1.15cm~(-1).     

二维分子的原子不对称性研究

基于分子形状的二进制编码提出了权原子和法来描述原子的不对称环境, 其中权原子和是以相反的方向环绕分子所得原子不对称环境的量度, 分子中一个原子的权原子和与其镜像分子中相应原子的权原子和的大小相等, 符号相反. 权原子和不仅适用于手性分子, 还能描述非手性分子中原子的不对称性. 与Randic′提出的原子和进行比较表明, 权原子和比原子和具有更好地区分能力, 因此, 权原子和能够更好地表征原子的不对称性.     

Periodic tables of diatomic and triatomic molecules

The Mendeleev periodic table of atoms is one of the most important principles in natural science. However, there is shortage of analog for molecules. Here we propose two periodic tables, one for diatomic molecules and one for triatomic molecules. The form of the molecular periodic tables is analogous to that of Mendeleev periodic table of atoms. In the table, molecules are classified and arranged by their group number G, which is the number of valence electrons, and the periodic number P, which represents the size of the molecules. The basic molecular properties, including bond length, binding energy, force constant, ionization potential, spin multiplicity, chemical reactivity, and bond angle, change periodically within the tables. The periodicities of diatomic and triatomic molecules are thus revealed. We also demonstrate that the periodicity originates from the shell-like electronic configurations of the molecules. The periodic tables not only contain free molecules, but also the "virtual" molecules present in polyatomic molecules. The periodic tables can be used to classify molecules, to predict unknown molecular properties, to understand the role of virtual molecules in polyatomic molecules, and to initiate new research fields, such as the periodicities of aromatic species, clusters, or nanoparticles. The tables should be of interest not only to scientists in a variety of disciplines, but also to undergraduates studying natural sciences.     

Periodic trends in constants of triatomic molecules

Working from the arrangements of both row and group numbers developed within Mendeleev's periodic table of elements, periodic trends can be shown to exist in many constants of triatomic molecules: an extension of the Periodic Law for atoms to the realm of molecules. Trends are identified for vibrational frequencies, bond lengths, and to a lesser extent interior angles. This work includes empirical sources for such data, supplemented with calculations using diatomic analogs where possible. Otherwise, computation is used for all possible configurations of row two and row three main‐group elements to both corroborate and extend empirical results. Organization of this data into a detailed, highly symmetric, multidimensional coordinate system allows for robust graphical and statistical analysis of all constants and associated trends, which in turn permits rapid identification of suspect data to be rechecked. All collected empirical and computational data, along with several interactive visualizations highlighting these results, is available online. © 2016 Wiley Periodicals, Inc.     

Interesting periodic variations in physical and chemical properties of homonuclear diatomic molecules

We carry out a systematic study of various ground state and response properties of homonuclear diatomic molecules (from hydrogen to rubidium, including transition metals) as a function of atomic number of constituent atoms. We perform the ground state and response property calculations by using state of the art density functional theory/time dependent density functional theory. We observe that several properties of homonuclear diatomic molecules show periodic variations along rows and columns of the periodic table. The periodic variations in the ground state properties of diatomic molecules may be explained by the nature and type of the bond that exists between the constituent atoms. Similarly, the periodic variations in the response properties such as static dipole polarizability and strength of the van der Waals interaction between diatomic molecules have been correlated with the variations in metallic/nonmetallic character of the elements along the periodic table. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Fuzzy Symmetries for Linear Molecules and their Molecular Orbitals

In this paper, the fuzzy symmetry of some prototypical linear molecules has been analyzed. The results show that some molecular orbitals (MOs) are less symmetrical but some others are more symmetrical than the molecular skeleton, which the MOs correspond to. The membership functions of space inversion for MOs are closely related to the chemical characteristics of the MOs. Sometimes, although the symmetry of a molecular skeleton is not obvious, however that of some MO is quite obvious. The membership functions of the fuzzy inversion symmetry depend on the choice of the position of the center of inversion. As compared to those of diatomic molecules and linear tri-atomic molecules, the linear polyatomic molecules in which a distinctive fuzzy symmetry of space translation may exist, and thus a significant effect on their properties can be expected.     

The UBI-QEP method: Basic formalism and applications to chemisorption phenomena on transition metal surfaces. Chemisorption energetics

The paper reviews the state of the art in the unity bond index-quadratic exponential potential (UBI-QEP) method. Assumptions made in the framework of the method, as well as their validity and generality, are discussed. The method is based only on well-defined observable energetic and structural parameters. UBI-QEP formulas for calculating reaction energetics (the binding energies of atomic and molecular adsorbates, the reaction enthalpies, and the intrinsic activation barriers) at different surface coverages are discussed. The UBI-QEP formalism is best suited for calculations of the adsorption of atoms and diatomic molecules but also allows one to consider polyatomic molecules in the quasi-diatomic approximation. A new formalism is discussed for determining the binding energies of various polyatomic molecules without resorting to hypothetical (and largely ambiguous) bond energy partitioning schemes. Instead, this new formalism considers the total bond energy of gas-phase species, which is an observable value. This formalism is the recent advance in the method. Various examples of calculating the energetics of atomic and molecular adsorption are presented. In most cases, the agreement of calculated and experimental values is good. The UBI-QEP method makes it possible to consider uniformly various processes on metal surfaces: adsorption, dissociation, diffusion, recombination, disproportionation, and desorption. Examples of complicated UBI-QEP calculations of molecular adsorption are presented.     

Electronegativity estimator built on QTAIM‐based domains of the bond electron density

The electron localization function, natural localized molecular orbitals, and the quantum theory of atoms in molecules have been used all together to analyze the bond electron density (BED) distribution of different hydrogen‐containing compounds through the definition of atomic contributions to the bonding regions. A function, g_AH, obtained from those contributions is analyzed along the second and third periods of the periodic table. It exhibits periodic trends typically assigned to the electronegativity (χ), and it is also sensitive to hybridization variations. This function also shows an interesting S shape with different χ‐scales, Allred–Rochow's being the one exhibiting the best monotonical increase with regard to the BED taken by each atom of the bond. Therefore, we think this χ can be actually related to the BED distribution. © 2014 Wiley Periodicals, Inc.     

Three related topics on the periodic tables of elements

Foundations of Chemistry - A large variety of periodic tables of the chemical elements have been proposed. It was Mendeleev who proposed a periodic table based on the extensive periodic law and...     

Accuracy and limitations of the pseudopotential method

Molecular model potential calculations have been performed within the SCF approximation on nine di- and triatomic molecules from the first row of the periodic table. We compare the molecular constants with ab initio SCF values and with model potential results obtained by other authors. Our results are accurate to a few per cent. The three most significant approximations in molecular model potential theory are: 1) The molecular model potential is the sum of atomic model potentials; 2) The atomic model potential is energy-independent; 3) The electron interaction model operator is l/r ₁₂. We arrive at the following general conclusions concerning these approximations: 1) The first approximation does not hold for strongly ionic molecules and for some highly excited molecular states. 2) Approximations 2 and 3 cancel to a large extent in molecules as they do in atoms, except in the case where approximation 1 breaks down. 3) Although various model- and pseudo-potentials yield reasonable results for atoms, not all of them are suitable for molecular calculations.     

Potential energy surface for linear triatomic molecules: An algebraic method

Recently, we proposed a new transformation between the angle of canonical coordinates and the bond angle to describe the bending motion in Potential Energy Surfaces (PES) of bent triatomic molecules. In this work we extend the transformation to include linear triatomic molecules. Results for the linear triatomic molecule N₂O are reported.     

Estimating local bonding/antibonding character of canonical molecular orbitals from their energy derivatives. The case of coordinating lone pair orbitals

According to Koopmans theorem, the derivative of the energy of a canonical molecular orbital (MO) with respect to nuclear coordinates quantifies its bonding/antibonding character. This quantity allows predictions of bond length variation on ionisation in a panel of 19 diatomic species. In polyatomic molecules, the derivative of a MO energy with respect to a given bond length reveals the nature and the degree of the bonding/antibonding contribution of this MO with respect to this bond. Accordingly, the HOMO “lone pairs” of CO and CN^? and the HOMO‐2 of CH₃CN are found to be antibonding with respect to the C? X bond (X = N, O), whereas the HOMO of N₂ is found to be bonding. With the same approach, the variation of the bonding character in the MOs of CO and CH₃CN on interaction with an electron acceptor (modeled through the approach of a proton) or by applying an electric field was studied. © 2016 Wiley Periodicals, Inc.