First-Principles Study Of The Adsorption Of Ag Atoms And Water Molecules On Silica Clusters

The adsorption of Ag atoms and water molecules on the silica clusters have been investigated using first-principles density functional theory(DFT).This dissertation is devoted to report the structure and electronic properties of the two systems.The main content is as follows:On the one hand,the interaction between Ag atoms and(SiO₂)_n(n=1-7) clusters have been detailedly studied based on DFT with generalize gradient approximation(GGA) with Dmol³.Firstly,we study the adsorption state of one Ag atom on the(SiO₂)_n(n=1-7) clusters.The results show that the Ag atom preferably binds to silicon atom with dangling bond in nearly a fixed direction.The effect of the adsorbed Ag atom on the bonding natures and structural features of the silica clusters is minor,and the adsorbed Ag atom only causes charge redistributions of the atoms near itself.In addition,the energy gaps between the highest occupied and lowest unoccupied molecular orbitals remarkably decrease compared with the pure(SiO₂)_n(n=1-7) clusters,eventually approaching the near infrared radiation region.This suggests that these small clusters may be an alternative material which has a similar functionality in treating cancer to the large gold-coated silica nanoshells and the small Au₃(SiO₂)₃ cluster.Secondly,we have analyzed the adsorption of multi Ag atoms on(SiO₂)₃ cluster.The incoming Ag atoms tend to cluster on the existing Ag cluster leading to the formation of Ag island easily, compared with the Au_n(SiOn2)n3 cluster.On the other hand,equilibrium geometries,adsorption energies,and electronic properties of a single water molecule on(SiO₂)_n(n=1-6) clusters have been investigated based on Gaussian 03.The detailed research indicates that a single water molecule preferably binds to silicon atom with dangling bonds and its plane is nearly parallel to the rhombus connected with itself.The water molecule primarily causes charge redistributions of the atoms near itself using the Mulliken charge analysis.In addition, we also report the interaction between(SiO₂)₃ cluster and multiwater molecules.Our results show that the hardness and energy gap between the highest occupied and lowest unoccupied molecule orbitals decrease as the number of the water molecules increases. The small silica cluster is not as easy as the nanochains to fracture and the Si-O bond breaking is mainly induced by the relatively isolated H₃O molecule.In addition,the infrared and Raman spectra are valuable in distinguishing among adsorption and dissociation of water molecules on silica.