First Principles Studies On The Reaction And Dynamic Behavior Of Several Surface Systems

With the rapid advances in experimental techniques, the development of surface science is considerable in recent decades. More and more knowledge has been gained on detailed and comprehensive understanding of surface progresses. Interpreting surface progress at the atomic scale, however, could still be regarded as a challenge. On one hand, conclusions on the same issue can be conflicting from different research groups due to the differences of the experimental conditions such as the preparation method, temperature, coverage and so on; on the other hand, some detailed information about surface progress and the corresponding microscopic mechanism cannot be obtained directly from experiments. As a result, theoretical calculations and modeling from first principles are indispensable.In the past decade, along with the development of the theoretical methods and programs as well as the improvement of the computational capabilities, first principles calculations can achieve the level of“chemical accuracy”; besides, it is also possible to model large systems with at most thousands of atoms such as surface. Now first principles calculations are greatly important in the studies of surface science. In this dissertation, I will show our studies on the adsorption, reaction and dynamic behavior of surface progress with first principles calculations. Through the comparison of simulation results with the experiments, some information of the detailed surface progress is obtained.In the first chapter, I give an introduction on the basic theoretical framework and the calculation methods employed in our studies. Firstly, I briefly introduce the Hartree-Fock method, post Hartree-Fock methods, and density functional theory （DFT）; then I show how to perform calculation under plane wave basis set, how to model surface system, and how to explorer reaction pathway and locate the transition state. After some information about the program package VASP, a brief introduction of scanning tunneling microscope （STM） and the corresponding simulation methods are given at last.In the second chapter, I first give a review of studies on the excitation and manipulation of adsorbed molecule with STM, and then I show our studies on the dehydrogenation progress of trans-2-butene molecule on Pd（110） surface, as well as the rotation and dissociation of oxygen molecule on the Pt（111） surface. In the studies of the adsorbed trans-2-butene molecule, we assigned the configurations of the reaction and product and explorer the dehydrogenation pathway. We found that the dehydrogenation is a step-wise progress following a barrierless rotation event. In the studies of the adsorbed oxygen molecule, we found an ingenious rotation pathway, which could explain the ultralow rotation barrier. In the studies of the dissociation progress, we locate an intermediate state with particular configurations. Combining the“cannon ball”mechanism, the prior occupation of the metastable hcp-hollow site after O₂ dissociation is explained.The third chapter of the dissertation focuses on the properties of adsorbed single molecule as a device: molecular switch. Firstly I give a brief review on the studies of this area, and then I show our results of two molecular switches: naphthalocyanine and melamine molecules. Through the studies of the tautomerization mechanism of the naphthalocyanine, we found that this molecule behaves as a four-state switch rather than a two-state switch. In the studies of the adsorbed melamine molecule, we found that this molecule adsorbs on the Cu（100） surface through a dehydrogenation progress. We provided an explanation on the dual functional properties of melamine molecule, and explored the whole progresses of the configuration changes under the STM stimulus after the adsorption. At last, we put forward a statistical model to explain the non-integral exponential relationship between the generation rate and the tunneling current, and successfully explain the observation from the melamine and oxygen molecule experiments.In the fourth chapter, we studies the diffusion dynamics of single Au, Ag and Cu atom on the Si（111）-7x7 surface. In the experiments it is observed that the diffusion properties of Au and Cu are in sharp contrast with the one of Ag. Through the analysis of the diffusion pathway and the adsorption energy changes, we found that the difference of the interaction between the adsorbed atom and the substrate is the main reason. In the case of Au and Cu, large interaction makes the displacement of the nearly Si adatom not too much, while for Ag, the displacement is larger, making the inter-basin diffusion barrier higher than the other atoms.In this dissertation, I include some other works which do not relate much on surface science. They include the photoelectron spectroscopy simulation of C₆H₄O（OH）- and C₆H₄O₂- anions, and the theoretical prediction of an ideal porous nano-structure as membrane for gas separation. These contents are put in the appendix.