The Molecular Dynamics Study Of Ammonia-Water Clusters

As aggregates of finite number of atoms at the microscopic level, clusters exhibit novel geometries,electronic properties as well as widely potential applications. The sudy of atom or molecule clusters can not only help to make more understanding of native properties of clusters, but also speed learning of properties of solid body .More and more interests have been abstracted for studing clusers both experimentally and theoretically. Recently years, the faint force between molecules gradually became the focus of clusters studies, hydrogen-bond as the typical represent of faint force has abstracted more and more reseachers'interests. Ammonia clusters, water clusters and ammonia-water clusters are binded by hydrogen-bonds, the structures and properties of these clusters have been studied by some researchers.Ammonia-water cluster as an important material of chemical industry and environment reforming has become the focus point of faint-force study fields. Daniel E.Bacelo studied the most stable structures of neutral NH₃(H₂O)n(n=3,4)clusters using the Density Functional Theory(DFT) methods , the geometries are similar with the neutral pure water clusters. The difference between these two clusters is that the water molecule is replaced by one ammonia molecule. The structures and properties of the electron ammonia-water cluster are seldom reported.Based on the work of the former people, inthis paper we investigated the possible structures of ammonia-water clusters using the density functional calculations employing the Becke-3 parameters with Lee-Yang-Parr functions(B3LYP) and using the 6-31+G(d,p) basis set. By structure optimizing and frequency analyzing, we obtained several possible low-energy structures. The most stable geometries of the (H₂O)5 NH₃ cluster by comparing their energy and the strength of hydrogen-bonds are obtained. The most stable (H₂O)5 NH₃ cluster structure are coincide with the structure which we obtained at HF/6-31+G(d) level. The result confirmed that the method of HF/6-31+G(d) is can believed. To save the calculating time, we studied the most stable structures of (H₂O)n (NH₃)m(m>1)clusters using Hartree-Fock method at 6-31+G(d) basis set level. Further more, we studied the structure of electron ammonia-water cluster [e+(H₂O)5 NH₃], this will do some help to further study on electron ammonia-water clusters. This paper consists of four chapters.In chapter 1, we presented the definition of atomic clusters, explained their properties , classified them and mentioned some difficult problems in study nowadays,as well as saw a good future.In chapter 2, we introduced some theory methods of clusters studies: the Hartree-Fock self-consistent local molecule orbital theory and the density functions theory.In chapter 3, we presented the basis functions used in Hartree-Fock method and the Density function theory. There are sorts of functions such as Slater functions, Gauss functions and mixed Slater and Gauss functions.In chapter 4, we investigated the geometries ,stabilities, binding energy, ionization potential and electron affinite of neutral ammonia-water clusters. Further more, we have performed primary study on electron ammonia-water cluster.