The Exploration Of Atoms In Molecules,Chemical Bonds And Atomic Charges From Chemical Quantum Topology Of The Kohn–Sham One-Electron Potential

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.