Atomic Structure, Stoichiometry, and Electronic Properties of CsPbI3 Quantum Dots Using Ab Initio Calculations

Ab initio calculations on atomic structures of charge-balanced CsPbI3 quantum dots (QDs) up to a size of similar to 2.5 nm show that cubic structures such as 2 x 2 x 2 and 3 x 3 x 3 are magic and should be more abundant than others in this size range. Also, 2 x 2 x 1 and 4 x 2 x 2 nanoplatelets have locally high stability. These results are in good agreement with experiments where the formation of cubic QDs or magic clusters as well as platelets has been reported. We find that it costs the least to detach Cs atoms from the surfaces of QDs. We used this as a strategy to find the stoichiometries of charge-balanced QDs and their lowest-energy structures. The electronic properties have been calculated with both the PBE form of generalized gradient approximation and the HSE06 hybrid exchange-correlation functional in density functional theory and by including effects of spin-orbit coupling. The calculated density of states shows quantum confinement with a local maximum in the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap for magic QDs and p orbitals of I (Pb) contributing near the HOMO (LUMO) as in the bulk. We hope that similar results will hold for other perovskite QDs in this family and further help in understanding the structures and properties of ligand-capped magic clusters/QDs, their assemblies, and QDs of other perovskites to explore new magic clusters of potential future materials for developing advanced perovskite semiconductor technologies.