Discrete size series of CdSe quantum dots: a combined computational and experimental investigation

Ab initio computational studies were performed for CdSe nanocrystals (NCs) over a wide variety of sizes ranging from 8 to 150 atoms in conjunction with recent experimental work. The density functional based calculations indicate substantial relaxations. Changes in coordination of surface atoms were found to play a crucial role in determining the NC stability and optical properties. While optimally (threefold) coordinated surface atoms resulted in stable closed-shell structures with large optical gaps, sub-optimal coordination gave rise to lower stability and negligible optical gaps. These computations are in qualitative agreement with recent chemical etching experiments suggesting that closed shell NCs contribute strongly to photoluminescence quantum yield while clusters with nonoptimal surface coordination do not.