Resolve The Surface And Interface Problem With Adaptive Genetic Algorithm

In the first chapter, we briefly introduce the basis of density functional theory?DFT? and the adaptive genetic algorithm ?AGA?. In the first part ?1.1-1.4?, we focus on the introduction of DFT. Due to the accuracy of DFT calculations and high performance of computing of parallel supercomputer, it is possible to predict the structure from different chemical composition. In the second part, we introduce the basic idea and process of AGA.In the second chapter, we briefly introduce the structure and electron structure of TiO₂ and the band edge position of anatase and rutile. And we talk about three way to get hydrogen energy from water, Photovoltaic electrolysis, Photoelectrolysis and Photocatalysis. We illustrate the mechanism of photocatalysis and three main problems promote photo catalysis effect, ?1? photon adsorption, ?2? charge carrier lifetime, ?3?surface reactivity.In the third chapter, we investigate the role of stress on reactivity of anatase ?001?surface, and solve the controversial between theory prediction and experiment. In contrast to the theoretical predictions in which anatase TiO₂ ?001? and its ?1×4?reconstructed surfaces are highly reactive, recent experimental results show this surface to be inert except for the defect sites. In this report, based on a systematic study of anatase TiO₂ ?001?-?1×4? surface using first-principles calculations,the tensile stress is proved to play a crucial role on the surface reactivity. The predicted high reactivity based on add-molecule model ?ADM? is due to the large surface tensile stress, which can be easily suppressed by a stress release mechanism. Various surface defects can induce stress release concomitantly with surface passivation. Thus, the synthesis of anatase ?001? surface with few defects is essential to improve the reactivity, which is proved can be achieved by small amount of H2O adsorption. Our study provides a uniform interpretation to understand the controversial experimental observations and theoretical predictions on anatase TiO₂?001? surface. It further proposes new insights to understand the origin of the surface reactivity.In the fourth chapter, we focus on the defect on anisate ?001?-?1×4? surface.Defects on oxide surfaces play a crucial role on the surface reactivity and thus it is crucial to understand their atomic and electronic structures. The defects on anisate TiO₂?001?-?1×4? surface are found to be highly reactive, however, due to the surface reconstruction, the defects exhibit complicated characters in different experiments which make it very challenging to determine their atomic structures. In this report, we present a systematic first-principles investigation of the defects on anatase TiO₂ ?001?-?1×4? surface based on a global-search adaptive genetic algorithm ?AGA? and density functional theory ?DFT?. For different Ti-O ratios, we identify the low energy defect structures, investigate their electronic structure using hybrid functional, and map their regions of stability under realistic conditions. We successfully find novel oxygen vacancy ?Ov? and Ti interstitial ?Tiini? structures that are different from the conventional ones in terms of their charge localization, magnetic state, and their scanning-tunneling-microscopy bright-dark signature. This provides insight into the complex geometric and electronic structure of the surface defects, and resolve several experimental discrepancies.In the fifth chapter, we study the morphology of supported Pt nanoparticles on MoS2 ?001? surface. The synthesis of Pt noble metallic nanoparticles which contains a few atoms on different supports is of high relevance for designing more efficient and less expensive catalysts. In order to understand the nucleation and epitaxial growth of Pt nanoparticles on MoS2 monolayers, we have systematically predicted and analyzed the structures of Ptn nanoparticles on MoS2?001?for n ? 55 using adaptive Genetic Algorithm. We give magic number of small Pt nanoparticles on MoS2?001?,and they are 7, 9 and 11. Almost all the low-energy structures are with layered hexagonal.When n>5, all the low-energy become layer structures. When n<20, all the structure are two-layered. And for Pt34 and Pt38, they are both three-layered. And Pt55 is four layered.In each layer, there are hexagonal layers. For low-energy structures, which are two-layered, they are all hcp stacking. In experiment, we synthetize Pt nanoparticles with only a few atoms. We also verify our theory results by Scanning transmission electron microscopy, a good match was achieved.In the last chapter, we make a brief summary and outlook to my future work.