The nanostructures of CdS and CdSe were modelled as Cd11S18H14 and Cd11Se18H14 clusters, respectively. The chosen facets of the models are the thermodynamically stable facet of the crystals (0001). To study the adsorption properties of the substrates on the model clusters, first, geometries of the substrates were optimized. Then the optimized structures were located on the model clusters. After that, we let them to relax on the clusters. To find the best position of the substrates on the clusters, we tested some different initial positions and we chose the lowest energy structures as the global minima. All calculations reported in the present study were carried out using density functional theory with the B3LYP functional [1]. For geometry optimizations, the 6-31G basis set was used for the C, O, S, Se and H atoms and the LANL2DZ pseudo potential for Cd [2]. Our results show that, the optimized geometry of each substrate obeys the same pattern on the clusters e.g., benzyl alcohol and benzoic acid are adsorbed perpendicularly and vertically, respectively on the both clusters. The calculated Eads of the substrates on the clusters are summarized in Table 1. According to Table 1, Eads of benzyl alcohol on both clusters is generally bigger than Eads of its oxidized forms (benzaldehyde and benzoic acid). In addition, the Eads of the substrates on the surfaces which is mostly covered by Cd atoms is bigger than the adsorption energies on the corresponding surfaces which are mostly covered by S or Se facets.
