Theoretical investigation for ZnSe clusters: Influence of solvent and ligand on their characteristics

On the basis of experimental zinc blende and wurtzite of ZnSe nanocrystals, four structures Zn3Se3, Zn4Se4, (Zn3Se3)2, (Zn3Se3)3 and Se-Zn-SR clusters were studied at DFT/B3LYP/LANL2DZ theoretical level. First, Zn3Se3, (Zn3Se3)2 and (Zn3Se3)3 structures have the same units (hexagon) with wurtzite. Zn4Se4 has resemblant conformation with zinc blende for they are all composed of tetrahedron. Second, calculated Raman peaks of Zn3Se3, Zn4Se4, (Zn3Se3)2 and (Zn3Se3)3 are about 180 cm−1 that is consistent with the experimental result. Third, through investigation of Se-Zn-SR clusters, we have found that their stability, bond lengths and the wavelengths of the absorption peaks do not have essential difference in theory. It illuminates that the main influence of ligand comes from thiol. Finally, we detect that both solvent and ligand make the wavelengths of the absorption peaks shift to blue. With solvent and ligand, our wavelengths of the absorption peaks will be almost identical with experimental ZnSe nanocrystals. Moreover, the wavelengths of the absorption peaks shift to red in order Zn3Se3, (Zn3Se3)2 and (Zn3Se3)3, which is induced by quantum size effect. Besides, we also prove that the calculated absorption peaks of four structures are the transitions from HOMO to LUMO or from d to p orbital.