First-principles Study Of Cadmium Sulfide Clusters And S Doped Wurtzite ZnO

In this dissertation, Computational Materials Science has been introduced in the firt chapter; in the second chapter, Density Functional Theory is introduced, which is the groundwork of Dmol³ and CASTEP packages; the lowest-energy structures and partial electronic properties of CdnSn (n≤9) clusters have been studied by Dmol³ package in the third chapter ; in the end chapter, the electronic structures of wurtzite ZnO, ZnS and S doped ZnO have been investigated by using first-principles ultrasoft pseudopotential modeling package—CASTEP.The lowest-energy structures and electronic properties of CdnSn (n≤9) clusters have been studied by using the generalized gradient approximation and all electron spin-unrestricted methods. Two dimensional ringlike structures have been found to be the lowest-energy configurations in the case of the smaller calculated clusters at n=2 and 3, and three dimensional spheroid configurations for the larger ones at n=4-9. It is especially interesting that the three dimensional structures may be imagined as being built from the Cd₂S₂ and Cd₃S₃ rings. Calculations show that the magic numbers of CdnSn (n≤9) clusters are n=3 and 6. The size of the lowest energy structure of Cd₉S₉ is about 0.72 nm.The electronic structures of wurtzite ZnO, ZnS and S doped ZnO have been investigated by CASTEP package. The calculation results indicate:the crystal constants increase with the quantity of S doping wurtzite ZnO; the top position of the valence band is determined by the S 3p electron state and it does not shift with the thickness of S-doping; the bottom position of the conduction band is determined by the Zn 4s electron state and it can shift to a lower energy position at first and then shift to a higher energy position with increasing S concentrations, the band gap of ZnO_1-xS_x is least when x is equal to 0.5. It is essential reason that the aberration of the crystal structure change with the thickness of S doping wurtzite ZnO.