Theoretical simulation of CdTe nanocrystals in aqueous synthesis

At the B3LYP/LANL2DZ theoretical level, Cd3Te3, (Cd3Te3)2, (Cd3Te3)3, Cd4Te4, and Te–Cd–ligand clusters were optimized. Firstly, hexagon Cd3Te3 and tetrahedron Cd4Te4 structures (with TD symmetry) may be the minimum units of CdTe nanocrystals. They have similar conformations with the experimental wurtzite and zinc blende structures, respectively. Secondly, the frequencies of calculated Raman peaks of four clusters appear in about 140 cm−1, which is close to the experimental data. Following, analysis of Te–Cd–ligand molecules elucidates that all our ligands have similar effect to CdTe structure, because the main influence of ligands comes from thiol, which is also the result of experiment. Finally, considering the influence of solvent and ligand, we believe that our wavelengths of absorption peaks which are calculated using the time-dependent density functional theory are perfectly identical with those of CdTe nanocrystals, according to quantum size effect. Moreover, we have testified that all these absorption peaks are the transition from d to p orbitals.