Understanding the effect of ligand exchange in CdS quantum dots from many-body perturbation theory

CdS quantum dots (QDs) are often synthesized with ligands binding to different facets of the QDs to passivate and eliminate the dangling bonds on the QD surface. A typical procedure used in the fabrication of CdS QDs is ligand exchange, replacing bulky ligands such as oleic acid with compact ones such as thioglycolic acid. However, a quantitative understanding of the effect of the ligand exchange on the electronic and optical properties of the CdS QDs is missing, which could impede an accurate determination of the QD size experimentally, where an empirical relationship between the QD size and the optical excitation is often used. In this work, we model various interfaces formed between the two ligands and different facets of CdS QD and employ the first-principles GW-BSE method to investigate how the ligand exchange quantitatively modulates the quasiparticle and optical properties of the CdS QD. Our results indicate that the ligand effects need to be taken into account in the experimental determination of the QD size.