Structure And Infrared Spectroscopy Of NH₄⁺（H₂O）₂₀ Clusters

Clusters are microscopic and submicroscopic particles aggregate. The number ofatoms, molecules or ions in a cluster is between several thousand to tens of thousands.Particles combined by physical or chemical force. The physical and chemicalproperties of a cluster are influenced by the number of particles and outsideenvironment, especially temperature and pressure. Cluster is a new substance betweenmacro and micro substance.The properties of a cluster are different from individualatoms and macroscopic matters, but also has a certain relation between them. Thestudy of clusters is not only beneficial to our in-depth understanding of clusters, alsohas an important guiding significance to the research of transition of matters from themicro to the macro. One of the main difficulties of Cluster research is that its isomernumber increases rapidly as the number of particles increasing. Determining theground-state structures of clusters is a very difficult and tedious work, but scientistshave developed a series of algorithms, laid a solid foundation to the study of clusters.Hydrogen bond cluster is an important member of the family of clusters, widelyexisting in the polarity solution such as water and ammonia. Hydrogen bonding is aspecial kind of interaction force between molecules, discovered in the early twentiethcentury. Due to its special nature in dissolution, energy transfer and chemical reaction,it has received the widespread attention. Both water and ammonia are good polarsolution, consisting of two special and important hydrogen bonds, which play a veryimportant role in the atmosphere, the formation of biological macromolecules, etc.Magic number was discovered when scientists researched the composition of thenucleus. The nucleus is made up of protons and neutrons. When the number ofprotons and neutrons is a specific value, the stability of the nucleus is larger than theaverage, and these values are called "magic number".The Study on ammonium ionized water clusters find that there are a series ofmagic number for them. When the number of water molecules of ammonium ionized water clusters NH₄⁺（H2O）nis20,21, etc, they have a good stability.Based on an model potential we got200kinds of original structures of the magicnumber ionized water clusters NH₄⁺（H₂O）₂₀. Then according to the energy and thenumber of occurrences in the process of model potential calculate we selected17kinds of structures. The selected17configurations divided into two categories-centerstructures and surface structures. Through configuration optimization and frequencycalculation, we found that all the structure without imaginary frequency. Then wecalculated the single point of each structure. By binding energy comparison we foundthe most stable structure for NH₄⁺（H₂O）₂₀cluster, and then we analyzed its vibrationspectrum. The results show that the center structures are more stable than the surfacestructures, and the center structure spectrum stretching vibration area is smaller thanthe surface structure.The main content of this paper are as follows:Chapter1: Introducing the development history of clusters, the classification of theclusters and related properties of clusters.Chapter2: Introducing the methods involved in the study of theory, including themodel potential, infrared spectra, density functional theory and Hartree-Fockequation, etc.Chapter3: Discussing the stability and infrared spectrum of the NH₄⁺（H₂O）₄clustersat the B3LYP/6-311++G（d,p） level.Chapter4: Discussing the stability and infrared spectrum of the NH₄⁺（H₂O）₂₀clustersat the HF/6-31G（d） level.Chapter5: Using the B3LYP method and6-31g （d） basis set for further structureoptimization and frequency calculation.Chapter6: Summary and outlook...