The Quantum Theory Of Atoms In Molecules(QTAIM) For The Intermolecular Weak Interaction And Chiral Molecule

In the Chapter 1,it mainly gave a brief of introduction to the basic theories and methods involved in this thesis,which included the development of the quantum mechanics and Quantum Theory of Atoms in Molecules(QTAIM),the core of QTAIM,the four critical points derived from the Hessian matrix,the BCP and bond-path properties of the QTAIM and stress tensor.In the Chapter 2,based on the theoretical basis of the next-generation QTAIM,we explored the competition between hydrogen and halogen bonds for the recently proposed Y=(Cl,Br,I,At)-halogenabenzene/NH3 complex.Differences between using the SR-ZORA Hamiltonian and effective core potentials(ECPs)to account for relativistic effects with increased the relative atomic mass demonstrated that next-generation QTAIM is a much more responsive tool than conventional QTAIM.Subtle details of the competition between halogen and hydrogen bonds were observed,indicating a mixed chemical character shown in the 3-D paths constructed from the bond-path framework set B.In addition,the use of SR-ZORA reduced or entirely removed spurious features of B on the site of the halogen atoms.In the Chapter 3,we sought to explain why the hydrogen bond possesses unusual strength in small water clusters that account for many of the complex behaviors of water.Therefore,we took the water clusters of H2O,(H2O)2,(H2O)4 and(H2O)6 as the research objects.We have investigated and visualized the donation of covalent character from covalent(sigma)to hydrogen bonds by calculating the eigenvector coupling properties of QTAIM,stress tensor ?(r),and Ehrenfest Force F(r)on the F(r)molecular graph.The next-generation three-dimensional(3-D)bond-path framework sets are presented,and only the F(r)bond-path framework sets reproduce the earlier finding on the coupling between covalent and hydrogen bonds has a certain degree of covalent characteristics.Exploration of the bond-path between the covalent and hydrogen bond's critical points provides an explanation for the previously obtained coupling results.The directional character of the covalent and hydrogen bonds's 3-D bond-path framework sets for the F(r)explains differences found in the earlier results from QTAIM and the stress tensor?(r).In the Chapter 4,we have previously found and located the unknown chirality-helicity equivalence in molecules with a chiral center,and as a consequence,the degeneracy of the S and R stereoisomers of lactic acid was lifted.As a result we located the "hidden" S-character chirality in the geometry-optimized structure of glycine that lacks a conventional chiral centre.This "hidden" chirality does not originate from its geometrical structure as in the conventional definition of enantiomers,but from the total electronic charge density distribution.This was realized by constructing the stress tensor trajectory in a non-Cartesian space,which defined by the variation of the position of the torsional bond critical point involving a four-coordinated carbon atom upon a structural torsion ?,-180.0° ?? ?+180.0° corresponding to clockwise and counterclockwise rotations.The robustness of this result was verified by applying a directional electric field to induce symmetry-breaking changes to create S and R stereoisomers.The preference for a S-character glycine stereoisomer persisted for modest electric field strengths that were not structurally distorting.In the Chapter 5,a summary and further work of this thesis.