Quantum dots (QDs) made of CdSe have attracted great attention in recent years.The CdSe QDs prepared under different conditions are usually different in size,structure,and property.Because of their complexity,the reaction mechanisms remain unclear for most of these reactions.There are many arguments on how a CdSe monomer is formed and how it grows.In this study,we performed computational studies on two aspects: i) The reaction mechanism of cadmium carboxylate with trimethylphosphine selenide: From density functional theory calculations,a new reaction path was proposed for the formation of CdSe monomer.The structures of some intermediates and by-products were identified and compared with measurements and previous predictions.Ⅱ)The growth pattern of magic-sized (MS) and regular-sized (RS) CdSe QDs: The fusion of selected small-sized CdSe clusters or QDs was studied with ab initio/force field molecular dynamics simulation.Four main patterns,monomer-by-monomer,RS-by-RS,MS-by-MS,and RS-by-MS,were examined to find out the energetically favorable paths for the formation of MS-QDs and RS-QDs.Our studies would be helpful for the development of new synthesis strategy of CdSe QDs.