The role of alkane chain in primary amine capped CdSe and CdS quantum dots from first-principles.

In this study, we perform ab initio calculations, using density functional theory, to provide more insights about the role of alkane chain in primary amine capped (CdSe)33 and (CdS)33 quantum dots (QDs). We passivate the QDs surfaces with seven primary amines of different carbon chain lengths starting from NH3 to hexylamine. The primary amine ligands induce a blue shift in the band gap of the ligated QDs, in agreement with experimental studies, but the alkane chain itself show negligible changes in the band gap. By increasing the chain length the binding energy between ligands and the QDs increases but its rate decreases due to the increase of steric hindrance between the ligands. The role of van der Waals forces in such behavior is found to be notable which is done by performing geometry optimization through adding and neglecting the dispersion correction effects for each system. The results of this study can provide helpful information for ligand selectivity in controlling the size and properties of the QDs using primary amines.