Theoretical study on influence of ligand and solvent to CdS clusters

摘要

Based on the experimental zinc blende and wurtzite structures of CdS nanocrystals, five new CdS clusters (Cd_3S_3, (Cd _3S_3)_2, (Cd_3S_3) _3, Cd_4S_4 with C_(2V), and Cd _4S_4 with T_D symmetry) are investigated via optimization of their original structures at B3LYP/Lanl2dz theoretical level. Through considering integration influence of solvent and ligand, our calculated Raman and absorption spectra can be consistent with the reported experimental results. First, our calculated Raman peaks of Cd_3S_3, Cd_4S_4 (T_D), (Cd_3S_3) _2, and (Cd_3S_3)_3 are within the range of 260-290 cm~(-1), which is also reported by experiment. Subsequently, for deep researching five clusters, the absorption spectra of them are calculated using time-dependent DFT method. The wavelengths of the absorption peaks, which is calculated in solvent, increase in the order Cd _3S_3, Cd_4S_4 (T_D), (Cd _3S_3)_2, and (Cd_3S_3) _3. Moreover, the wavelengths of absorption peaks shift to blue in solvent, compared with those without solvent. Furthermore, our clusters are smaller than the size of the smallest CdS nanocrystals, the calculated absorption spectra of five clusters in solvent show obvious blue shift than the wavelengths of absorption spectra of reported CdS nanocrystals. This is induced by the quantum size effect. Besides, we further investigated the influence of ligands to CdS unit in aqueous condition. Through structures and characters analysis of S-Cd-SR, we discovered that ligands took important role during the formation of CdS nanocrystals in aqueous synthesis. Calculated results of spectra, bond length, and Wiberg bond index (WBI) values show that different ligands have similar influence on CdS unit. Moreover, using WBI values, we also confirm that Cd atom has stronger interaction with S in nanocrystals than that with S atom in ligand.