Construction Of Potential Energy Surface And Molecular Dynamics Simulation Of The Reactions Of Metal Clusters

Molecular Dynamics (MD) has been widely applied to the investigation of reaction dynamics of prototype reactions and complex systems, for example H2+F, and protein folding. However, reliable investigation of physical and chemical properties of metal cluster via MD method is still absent. As promising material and catalyst, the dynamic properties of metal clusters like aluminum and gold clusters under high temperature is the hot spot of experiments. Therefore, study of the dynamic properties of metal clusters like gold and aluminum clusters under high temperature will not only broaden the application area of molecular dynamics but also deepen our comprehension of the change of catalysis center during the catalytic process and provide theoretical evidence and knowledge for experimental development of novel catalysts.Owing to the expensive cost of ab-initio calculations, the deficiency of accurate classical potential energy surface, and lack of experimental methods, the structure and dynamic properties of metal clusters in the catalytic process are still unclear to us. Thus, this thesis mainly focuses on the collision between of alluminum clusters via molecular dynamics simulation and the building of accurate semi-classical potential energy surface for gold clusters:Analysis of differential cross section (DCS) of collisions between aluminum clusters:Through the investigation of correlation between different observable variables, such as angular momentum of products and reactants, the temperature, shape, and angular momentum of the reaction intermediates, and product distribution, we have summarized the general rule of collision between aluminum clusters, which may also be applied to the collisions between other metal clusters. Based on the finding that the intermediate of the collisions is ellipsoid sphere and the selectivity over products is controlled by both kinetic and thermodynamics factors, we proposed a novel model to explain the DCS patterns of aluminum cluster collisions. Moreover, this work shows that NPB, a new form of potential energy surface, is able to describe the dynamics behavior of aluminum clusters well and can be applied to other systems as well.Validation of density functional theories for the calculation of gold clusters: In the purpose of building the database required by PES construction, we have systematically studied the performance of various density functional theories for the calculation of gold clusters. It turns out that Spin-Orbit (SO) coupling overestimates the cohesive energy of gold clusters, while Hartree-Fock exchange underestimates the cohesive energy of gold clusters. Due to the cancelling effect between SO effect and HF exchange TPSSh was found to be the best method for gold clusters. Through further study of the relationship between SO correction to atomization energy (ΔESO) and the size of the gold clusters (Natom) and the number of Au-Au bonds (Nbond), a simple linear equation betweenΔESO and Natom and Nbond has been found, which may help to solve the puzzle regarding to the transition point of gold clusters from two-dimensional (2D) structures to three-dimensional (3D) structures.Transition of gold clusters from 2D structures to 3D structures:Two methods, M06 and TPSSh which have good performance in the calculations of gold clusters have been used to study Au6-Au13 clusters and the results were compared to those calculated by M06-L which was recommended by previous studies indicating that M06-L can reproduce the 2D-3D transition points of ionic gold clusters observed by experiments. It turns out that SO coupling is very important on the determination of the 2D-3D transition of gold clusters and both M06 and TPSSh give the same result on this issue. However, the performance of M06-L is not very satisfactory. Furthermore, it was also found in the present study that SO coupling prefers high symmetry geometries. Finally, through the comparison between experimental and calculation results, Au7 was found to be the largest neutral gold cluster dominated by planar structures.Building of gold potential energy surface:We have scanned the potential energy surface of Au2-Au4 using the accurate SO TPSSh method which was validated in the previous benchmark calculations. The resulting energies were fitting into NPB via differential revolution method. The fitting is very successful and the error is only 0.015 eV/cluster.