The Study Of Catalytic Activity On Single Gold Atom And The Nature Of Gold Alloys Melting Points Via First Principle

It is well known that the geometrical structure is very important for the properties of material. Nowadays, a lot of novel materials are discovered and we need to understand the relationship between structure of materials and their properties. Knowledge of geometrical structure is helpful for us to design new materials. Gold (Au) is the most famous noble metal and in the present thesis, we study the structure of single Au atom embedded in BN sheet and Au alloy (Al2Au), mainly focused structure effect on their properties. It is found that the melting points of Au alloy as well as the catalytic activity of Au atom largely rely on the geometrical structure. The geometric structure, liquid local structure analysis, cohesive energies were identified by performing the first-principle calculation. The effect of electronic structure and spin orbit coupling was also discussed. The contents of this thesis were shown below:In the first chapter, the background knowledge on first-principle calculation method which is based on density functional theory was introduced, including exchange-correlation functional, ultra-soft pseudopotential and k-points sampling. For instance, local density approximation (LDA), generalized gradient approximation (GGA), hybrid functional, etc. Besides, different atomic potentials, molecular dynamic methods and some mostly used first-principle codes were also introduced.In the second chapter, the origin of different melting points between Al2Au and Al2Cu was discussed. Spin orbit coupling has been taken into account since it has a significant effect on heavy element, such as gold. It is found that the SOC effect affects the cohesion energy of crystal phase, which is believed to be the main reason for their different melting points. Moreover, the d-projected local density of states projected onto Au and charge densities are analyzed and a gap was found due to d-orbital splitting in Al2Au.In the third chapter, we calculated the liquid atomic structural evolutions of both systems by using ab initio molecular dynamics simulations. The atomic configurations have been analyzed by several statistics methods such as pair correlation function g(r), bond angle distributions, Honeycutt-Anderson (HA) index and Voronoi tessellation index. It is found that the liquid local atomic structure of Al2Au is distinct from Al2Cu. It reveals that the origin of this appearance might be the random atomic positions of liquid phase, which reduces the SOC effect on amorphous system.In the fourth chapter, we investigated the interaction between Au atom and one atom thick hexagonal BN sheet with and without single-atom vacancy. The catalytic activity of Au-embedded BN is probed using the CO oxidation as a benchmark. It is found that the chemical activity depends on vacancy type:boron vacancy (VB) or nitrogen vacancy (VN). It cannot active CO oxidation when boron atom is substituted by Au atom (Au-VB). While the CO oxidation can be largely activated by the nitrogen-substituted (Au-VN) BN sheet without barrier almost.In the fifth chapter, we summarized the projects I have done during my postgraduate study, and prospect the future research work.