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

Abstract

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.