DFT study for the absorption spectra evolution of CdS magic-size clusters

Absorption spectroscopy is important and necessary for the study of magic-size clusters (MSCs). However, researches regarding the relationship between the structural change and absorption spectra variation are quite limited. Herein, we compared the structural variation and absorption evolution of MSCs by first-principles calculations in this paper. Firstly, we simplified the single crystal structure In₃₇P₂₀(OOCCH₂Ph)₅₁ of InP MSC to In₃₇P₂₀H₆₈ and calculated its absorption spectrum using three different functionals (PBE, B3LYP, HSE06). By comparing the absorption spectra calculated from the In₃₇P₂₀H₆₈ structure with those measured from the InP MSC sample, we evaluated the difference in absorption spectra calculated by different functionals and the rationality of this kind of method for structure simplification. Secondly, we validated the structural model Cd₃₇S₂₀ proposed for CdS MSC-311 by calculating the absorption spectrum of Cd₃₇S₂₀H₆₈ and comparing the similarity between the absorption spectrum calculated and the experimental measured. Finally, we expanded structures based on the principal characteristics of Cd₃₇S₂₀ and calculated the corresponding absorption spectra of them. By comparing the difference among the absorption spectra of the expanded structures, we demonstrate that the absorption peak position shifts of MSCs are more sensitive to their anisotropy, instead of the number of atoms added and local structure change. These findings provide an in-depth understanding of the structure-absorption relationship.