【作者】 赵健；

【导师】 赵东霞；

【作者基本信息】 辽宁师范大学 ， 物理化学， 2020， 博士

【摘要】 分子中的原子,化学键和原子电荷都是化学的重要和基本的概念,对其的研究和探讨颇受重视。量子化学拓扑(QCT)是理论化学的一个新兴分支,它使用动力系统的数学语言,探讨与分子有关的标量场,进而分割和表征化学体系的性质。本文采用密度泛函理论(DFT)中的Kohn–Sham单电子作用势(KSpot)作为标量函数,提出和建立KSpot的QCT理论,即KSpot QCT。首次探讨了分子的KSpot及KS力的空间特性,给出分子中的原子和化学键概念的新定义,研究和探讨双原子和多原子分子以及复合物体系的结构和性质,获得KSpot原子电荷。具体内容如下。探讨KSpot和KS力的空间特征。在两个成键原子的区域内,KSpot势能面有一个鞍点,该点在沿着和垂直化学键方向上分别对应KSpot的极大值和极小值,该点处的电子坐标称为键临界点。利用KSpot的梯度负值,即KS力,可以将分子分割为互不重叠的原子区域,这些力线始于无穷远,止于键临界点,这些线构成的曲面为原子间的分界面,获得了分子中的原子。化学键为两原子间经过键临界点的连线,即该连线邻域KSpot极小值路径。获得无机、有机、生物小分子和复合物的KSpot原子电荷。积分各个原子区域的电子密度,获得KSpot原子电荷。该电荷对纯泛函方法和基组的依赖性小。从50个双原子和12类223个多原子分子的KSpot电荷,发现KSpot电荷数值比QTAIM数值小,而比Hirshfeld数值大,介于两者之间。KSpot原子电荷能重现从头计算的分子偶极矩和静电势,故KSpot原子电荷数值合理。另外,我们还拓展KSpot的应用,包括利用键临界点处的KSpot估算氢键强度,展示分子轮廓,表征分子区位和立体选择性。总之,我们提出的Kspot QCT将量子力学和经典化学概念联系起来,给予了分子中的原子和化学键一种新定义,并获得了对基组依赖性小且数值合理的KSpot原子电荷。这种方法有望应用于分子力场的构建,结合机器学习探索大分子性质,进而在生物分子,高分子和材料等领域发展。更多还原

【Abstract】 Atoms in molecules,chemical bonds and atomic charges are all foremost and fundamental concepts in chemical science,which have received increasing attention and investigation.Quantum chemical topology(QCT)is an emerging branch of theoretical chemistry,which uses the dynamical system language to partition and character chemical system via associated scalar functions.Within the framework of QCT,Kohn–Sham potential(KSpot)of one electron in density functional theory(DFT)is regarded as a new scalar function that is proposed and constructed the KSpot QCT,which reveals molecular spatial characteristics,new definitions on atoms in molecules and chemical bonds,then the resultant atomic charges for the first time.The details are as follows.The exploration of spatial characteristic about KSpot and KS force.There is a saddle point on the KSpot potential surface between two bonded atoms regions,which is a KSpot maximum and two minima along and perpendicular to the chemical bond,respectively.Its electron coordinate corresponds to the bond critical point.The negative gradient of KSpot is defined as the KS one-electron force lines partitioning one molecule into non-overlapping atomic realms,which start from infinite and end at the bond critical point.The surface constituted by these KS one-electron force lines is separatrix between two atoms.Furthermore,the atoms in molecules are defined.In light of the KSpot QCT,chemical bond is a line between two bonded atoms through the bond critical point,which is a KSpot minimum path in its vicinity.KSpot atomic charges of inorganic,organic,small biomolecules and complexes.The integration of electron density over the atomic realms obtains the KSpot atomic charges that have little dependence on the generalized-gradient approximation methods and basis sets chosen.With regard to the atomic charges of 50 diatomic and 223 polyatomic molecules classified into 12 types,we have found that the KSpot atomic charges possess intermediate values between those obtained from the QTAIM and Hirshfeld methods,i.e.,they are larger than Hirshfeld ones but smaller than the QTAIM ones.And KSpot atomic charges are reasonable,because they can reproduce the molecular dipole moments and electrostatic potentials calculated from ab initio.Moreover,the KSpot QCT has been used in other applications,including evaluation of the strength of hydrogen bonds by the KSpots at bond critical points,showing molecular contours,and characterization of region-and stereoselectivity.In a nutshell,the proposed KSpot can bridge quantum mechanics and classic chemical convention,which is a new definition of atoms in molecules and chemical bonds and gains KSpot atomic charges that are little dependence on basis sets and possess reasonable values.In the not distant future,this method is promising to build a new molecular force field,study properties of macromolecules combined with machine learning,and further develop in the fields of biological molecules,polymers and materials etc.更多还原