| Hydrogen bonding is the most common weak interaction in chemistry, biochemistry, crystal assembly, medical research and even plays a very important role in the supramolecule field. The supermolecule study is the basic study in the field of materials science, so for the research of hydrogen bonding properties in the 21st century has become a hot issue. The purpose of this research is using quantum chemistry methods and tools, combined with Bader,theory of "atoms in molecules (AIM theory)", to carry out detailed topological analyses of the electron density for the nature of the classical hydrogen bond, theπ-type hydrogen bond and single-electron hydrogen bond.This second chapter outlines the development course of quantum chemistry and its development status. In recent years, with the rapid development of experimental techniques, more and more sophisticated techniques such as ESR, IR, electronic spectra, have been used to study the electronic structure of molecules and atoms. The combination of experiment and theory, analytical techniques and quantum chemistry theory, makes the study on the electronic structure of molecules and atoms be more and more accurate.This third chapter let N2O molecule as the research object, with HX (X = F, Cl, Br) molecules form a hydrogen bond system and conducted a detailed study. The results show that there are two kinds of bond types with the N-atom or O-atom, respectively. Then detailed topological analyses of the electron density have been carried out using Bader,AIM theory.This fourth chapter using CH3CN molecule as the electron donor for the hydrogen bond, discuss the hydrogen bond systems with the H2O molecule and HX (X = F, Cl, Br) molecules. Topological analyses of the electron density have been carried out, and detailed studies have been performed on the proton donor H atom, including the net charge, atomic volume, dipole moment, atomic volume changes .This fifth chapter studies the hydrogen bond systems formed by C6H5F molecule and CHF3,CHCl3 molecules. There are three types of hydrogen bonds, including hydrogen bond as aπ-type hydrogen bond, also known as blue-shifting hydrogen bond. Studies on the molecular configuration parameters, the interaction energies, topological properties and the integral nature of the H atoms have been carried out. The detailed study found there are many similarities in blue-shifted hydrogen bond and classic-type hydrogen bonds,.Chapter VI of this article studies the hydrogen bond systems formed by free radicals CH3O or CH3S and HX (X = F, Cl, Br) molecules. The configuration parameters and topological nature were studied. In order to study the single-electron hydrogen bond systems, theαelectron density andβelectron density have been separated using ZGTA09 program package, which was complied by our research group. Contour maps of the spin electron density have been plotted, which illustrate the single-electron hydrogen bonding characteristics.The innovations in this paper:(1) A detailed study on the classical hydrogen bond, non-classical hydrogen bond, and single-electron hydrogen bond have been carried out. Topological analyses of the electron density found that: with the formation of hydrogen bonds, the net charge of proton donor H atom increases, the atomic energy increases, the dipole moment decreases and the atomic volume is reduced.(2) In order to study the single-electron hydrogen bond systems, theαelectron density andβelectron density have been separated using ZGTA09 program package, which was complied by our research group. Contour maps of the spin electron density have been plotted, which illustrate the characteristics of the single-electron hydrogen bond. (3) The ZGTA09 program package, which was compliled by our research group, was used to study the classic hydrogen bond, non-classical hydrogen bond, and single-electron hydrogen bond. Contour map of the Laplacian of the electron density were plotted, which illustrate the hydrogen bonding characteristics and its essence.
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