【作者】 杨华；

【导师】 胡维军；

【作者基本信息】 山东师范大学 ， 理论物理， 2009， 硕士

【摘要】 团簇是由几个乃至上千个原子、分子或离子通过物理或化学结合力组成的相对稳定的微观或亚微观聚集体。团簇是一种新的物质形态,对团簇结构与性质的研究不仅可以深入了解团簇本身的性质,而且有助于进一步理解物质从微观到宏观过渡具有的重要作用。团簇具有特殊的物理化学性质和明显的尺寸依赖性,这引起了物理、化学和材料等领域的广泛关注。团簇结构存在许多异构体,并且异构体的数目随团簇尺寸的增大迅速增长,理论上要确定一个团簇的最稳定结构是非常困难的工作,对分子团簇这个问题将变的更加困难。然而团簇的物理化学性质主要决定于团簇的基态结构,所以确定团簇的可能稳定结构并由此推断出其基态结构是解决团簇问题的基本问题。近年来,氢键团簇成为人们研究的重要课题,氢键作为分子间的相互作用力在很多科学问题中扮演着重要的角色,如溶解、能量转移和化学反应都离不开氢键的作用。氨水团簇存在O···H和N···H两种特殊而重要的氢键,对其进行深入的研究,可以更好的解释大气、生物大分子的形成,同时氨水作为典型的极性可溶性溶剂,在工农业、制冷和能源等领域有着广泛的应用。近来,对氨水团簇的研究正逐渐受到人们越来越多的重视。Paul A. Stockman等人测得了在一定条件下线性氨水二聚物的微波和可调红外激光谱。Daniel E.Bacelo等人利用AB initio方法在理论上探寻了中性氨水团簇的结构和频谱,发现（NH3）（H2O）3和（NH3）（H2O）4团簇的可能稳定构型为平行四边形环状结构。Subha Pratihar等人利用密度泛函和二级微扰方法探寻了更为复杂的中性氨水团簇（NH3）m（H2O）n（p=m+n=3-7）的结构和频谱,发现p=3-5的最稳定构型为平面环状结构,而p=6-7时最稳定结构为笼状结构。本文分别用密度泛函方法（DFT/B3LYP）和二级微扰方法（Moller-Plesset/MP2）在6-31G（d,p）和6-311++G（d,p）基组水平上逐级对（NH₃）₂（H₂O）₂团簇和NH3（H2O）4团簇进行结构优化和频率计算。初始结构取自经验势模型中的稳定性较好的构型,最终得到了在B3LYP/6-311++G（d,p）水平下的9种（NH₃）₂（H₂O）₂团簇及15种NH3（H2O）4团簇稳定结构。分析发现:正四边形环状结构为（NH₃）₂（H₂O）₂团簇的最稳定构型,NH3（H2O）4团簇的五边形环状结构的稳定性最好;团簇频移的大小及谱线强度的变化与氢键类型有着密切的关系,频移大小主要取决于氢键的施体数目;偶极距的大小与结构的稳定性无必然联系,这与以前文献的结论不同本文的主要内容有:第一章:团簇科学的介绍,阐述了团簇的概念、性质、分类以及团簇研究的现状、困难、意义和前景。第二章:介绍了本课题研究中使用的理论计算方法,包括分子轨道理论密度泛函理论、自洽计算中的基函数以及振动频率的计算,并且本章对计算软件Gaussian 03程序加以说明第三章:在B3LYP/6-31G（d）水平和B3LYP/6-311++G（d,p）水平计算了NH₃（H₂O）₄可能稳定结构及频谱进行初究。发现NH₃（H₂O）₄团簇的五边形环状结构的稳定性最好。第四章:在B3LYP/6-31G（d）水平和B3LYP/6-311++G（d,p）水平对（NH₃）₂（H₂O）₂团簇稳定结构及频谱展开探究工作,发现正四边形环状结构为（NH₃）₂（H₂O）₂团簇的最稳定构型。更多还原

【Abstract】 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. The study of the structure and properties of clusters can not only insight into the nature of the clusters, but also contribute to a better understanding of the material from the micro to the macro transition. Clusters have special physical and chemical nature and the obvious size-dependent, which led to widespread concern of physical, chemical and materials flieds. Clusters exist many isomer structures, and the number of isomers increases with the rapid growth of the size. It is very difficulty to find the most stable structure in theory,and more difficult to the molecular clusters. However, the physical and chemical properties of clusters mainly depend on the ground-state structure, therefore it is a basic problem to find the stable structures of clusters and infer the ground state structure for the cluster problem.In recent years, the hydrogen bond clusters become important research topics. As interaction force between the moleculars, hydrogen bond plays an important role in scientific issues. Dissolution, energy transfer and chemical reactions all can not be separated from hydrogen bonds. Ammonia and water clusters exist O ? ? ? H and N ? ? ? H which are special and important hydrogen bonds, and with the in-depth research, it can better explain the atmosphere, the formation of biological macromolecules. At the same time, as a typical soluble in polar solvents, the ammonia and water have a wide range application in the industrial and agricultural, refrigeration and energy and other fields. Recently, the study of ammonia and water clusters is gradually attracting more and more attention. Paul A. Stockman and others measured microwave and tunable infrared laser spectroscopy of ammonia and water dimer linear at certain conditions. Daniel E. Bacelo explore structure and the spectrum of the neutral ammonia and water cluster with AB initio methods, and found that the possible stable configurations for（NH3） （H2O） 3 and （NH3） （H2O）4 clusters both are parallelogram ring. Subha Pratihar and others research the structure and spectrum of more complex clusters of neutral ammonia （NH3） m （H2O） n （p = m + n = 3-7）,and found the most stable configuration is the planar ring structure for p=3-5 and the cage-like structure for p = 6-7.The structures and Infrared Spectra of NH₃（H₂O）₄ and （NH₃）₂（H₂O）₂ clusters were investigated using density functional theory methods （DFT/B3LYP） and M?ller-Plesset second-order perturbation method （MP2） with the 6-31G（d） and 6-311++G（d, p） basis sets. As the first step, 39 among 127 stable geometries of NH₃（H₂O）₄ clusters and 48 among 133 stable geometries of （NH₃）₂（H₂O）₂ clusters resulted from an empirical potential model, were selected as the initial input configurations for the ab initio calculations. Secondly, a DFT/B3LYP calculation of structural optimization and infrared spectra was performed with 6-31G（d） basis set for the selected geometries, and 30 stable structures of NH₃（H₂O）₄ clusters and 29 stable structures of （NH₃）₂（H₂O）₂ clusters have been obtained. Finally, the B3LYP/6-31G（d） stable structures were further optimized using the same theory level and a bigger 6-311++G（d, p） basis set, and, as a result, 15 stable structures of NH₃（H₂O）₄ clusters and 9 stable structures of （NH₃）₂（H₂O）₂ clusters have been obtained. It is found that, to our knowledge, 11 among the 15 structures of NH₃（H₂O）₄ clusters have not been reported in the previous literatures. The result indicates that the pentagon structure is the most stable structure of the NH₃（H₂O）₄,and the square structure exist as the most stable structure of the （NH₃）₂（H₂O）₂ clusters. in consistent with the previous reported calculation; the shifts and intensity of the frequencies have close relation to the H-bond types. Also, it is found that the shift is strongly dependent on the number of donors of H-bond, and that there is not certain association between the dipole moment and the stability of the clusters, which of the conclusion is different from previous literatures.更多还原