| Clusters are composed of some atoms or moleculars,and the number of the atoms or moleculars in a cluster has a range from several to thousands.Clusters,as a new form of substance,show many novel and unique properties both in physics and chemistry.The detailed knowledge of the atomic structure of clusters,and the dependence of structure on size is an intriguing issue.Due to their unique geometrical arrangements,physical,chemical,electronic and magnetic properties,the studies of clusters can greatly facilitate and promote the fundamental and applied research of many related subjects,such as physics,chemistry and materials.The electronic structure and chemical bond of cluster dominate geometric configuration,contrariwise,geometric configuration reflects the feather of chemical band and electronic structure.Therefore,unambiguous assignment of the ground state geometric configuration is a principal task.In the past decade,cluster science has brought tremendous advances in the study of weak bond clusters,especially hydrogen-bonded clusters.The hydrogen bond is a weak chemical interaction that plays a significant role in many areas of chemistry.Many phenomena such as solvation,energy transfer and chemical reactions are influenced by the hydrogen molecules.Water and ammonia are both important hydrogen bond clusters.Study on water-ammonia clusters has been an active field.In experiments C.Desfrancois,et.al.,have produced(NH3...H2O)- dimer under very specific experimental conditions.Its existence is a test of theory,that the extra electron is bound by a dipole interaction in the cluster.This cluster has a very small electron binding energy.Hu yong jun,et,al.,studied the multiphoton ionization of the ammonia clusters at 355nm using both conventional and reflection time-of-flight mass spectrometers.A series of protonated ammonia clusters(NH3)nH+ were obtained,and the hypervalent ammonia cluster ions(NH3)nH(2+)(n＞2)were observed. In theoretical calculation,Titus A.,Beu and Udo Buck calculated ammonia clusters with size range from n=3 to 18 using a parwise additive model potential.The trimer and teramer are stable cyclic configurations.From the petramer onward the structures are three dimensional with an increasing tendency to amorphous behavior.Wang Qing et.al.,carried out optimization on nH2O…mNH3 at the HF/6-31+G(d,p)and MP2/6-31+G(d,p)levels and interaction energies had been compared.Subha Pratihar and Amalendu Chandra investigated the structure and energies of water ammonia mixed clusters with an excess electron, [(H2O)n(NH3)m]-(m=1,n=2-6 and m=2,n=2),by means of ab initio quantum chemical caculatins.It is found that the hydrogen-bonded structure of the anionic clusters are very different from those of neutral clusters.In this paper,Hatree-Fock theory and density funtional theory calculation has been carried out on structure of water-ammonia neutral and anionic clusters,ground state structures were found.It is found that only surface binding state for n=2.However,for n=3 and 4,both surface and interiorlike binding states are found to exist for the excess electron.In Chapter1,we firstly introduced the concept,meaning and methods of research on ammonia clusters.Then,the research actuality of the subject is listed.In Chaper2,we introduced some theory methods of clusters:the Hatree-Fock theory and density functions theory.In Chapter3,geometries of the neutral and anionic isomers were refined in HF/6-31+G(d,p),some of the structures were further optimized at B3-LYP level with the 6-31+G(d,p)basis set,the stable equilibrium conformation of neutral cluster was found to be a cyclic structure,and the stable equilibrium conformation of anionic cluster was found to be a lineal structure.In Chapter 4,B3LYP/6-311++G**density funtional theory calculation has been carried out on structure and frequency of[NH3(H2O)n]-(n=2-4)cluster,ground state structures the excess electron binding states were found. |
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