Ligand Effect On The Nucleation Of Thiolate-protected Gold Nanoclusters And The Rapid Search Algorithm For The Optimal Surface Ligand Configuration

Gold nanoclusters possess unique physical and chemical properties and have attracted much attention from researchers because of their great potential for applications in the fields of luminescence,catalysis,and biomedicine.The experimental synthesis of Au_m（SR）_n nanoclusters has been carried out by two-phase synthesis,seed growth,alloying and ligand exchange methods.A large number of experimental and theoretical studies have revealed that SR ligands can significantly modulate the stable structure and size transformation of Au_m（SR）_n nanoclusters in recent years.For example,ligand exchange method is a widely used method for the synthesis of Au_m（SR）_nnanoclusters in recent years.Using ligand exchange to induce structural changes in the structure of gold clusters,it is possible to achieve cluster isomerization,size growth or shrinkage and obtain some new cluster species.Therefore,it is of great importance to study the stabilization effect of thiolate ligands on the overall structure of gold nanoclusters and the effect of steric site resistance of ligands on the nucleation path of clusters to understand the formation,stabilization and evolution mechanism of such clusters.In this paper,using theoretical tools such as molecular mechanics,density flooding theory（DFT）,and genetic algorithms to model the structures of recently experimentally synthesized clusters such as Au₂₈（TBBT）₂₀ and Au₂₈（CHT）₂₀.The research content is mainly divided into the following two parts.（1）The first-principles density generalized theory calculations were used to investigate the"bottom-up"nucleation pathways of Au₂₈（TBBT）₂₀ and Au₂₈（CHT）₂₀clusters with heterostructures.Firstly,the zero-electron（0e^-）reaction precursors and the reaction equations for each two-electron（2e^-）nucleation step were deduced backwards from the structures of the two clusters;on this basis,the nucleation growth paths of the two Au₂₈ clusters were obtained by constructing intermediate structure models and DFT structure optimization to optimize the structures and energies of the reaction intermediates.The calculation results showed that the SR ligand significantly regulated the selectivity of the growth paths of the clusters,and the regulatory effect on their final structures was related to the intermediates of the growth process.（2）A computational method based on the combination of molecular force field and genetic algorithm for fast search of the most stable ligand conformation on the surface of Au_m（SR）_n nanoclusters was designed.The feasibility of the theoretical method was first tested with the recently experimentally reported gold clusters Au₂₀（TBBT）₁₆,Au₂₈（TBBT）₂₀,Au₃₆（TBBT）₂₄,Au₅₂（TBBT）₃₂,[Au₂₃（CHT）₁₆]^-,Au₂₈（CHT）₂₀,Au₃₄（CHT）₂₂,etc.The calculation results show that the conformational search method proposed in this paper can quickly lock the dominant ligand conformation and provide reasonable candidate structures for the next step of DFT energy calculation ordering.Through the DFT energy calculation,this paper also found some cluster surface ligand conformations with lower energy than the experimental crystal structures.There are two possibilities for this result.It is due to the error of DFT energy calculation or the ligand orientation may have changed during the formation of the clusters.Using this calculation method,this part of the work was further searched for the dominant conformation of Au₁₅（SR）₁₃ clusters under the protection of four different SR ligands.It was found that the structure with the core protected by a seven-membered ring was the dominant structure under the protection of TBBT ligand,CHT ligand and p-MBA ligand,and the structure with the core protected by a six-membered ring was the dominant structure under the protection of S-Adm ligand.This calculation provides a new theoretical perspective to further clarify the unknown structure of the Au₁₅（SR）₁₃ cluster.