Reactive Force Field Modeling of Zinc Oxide Nanoparticle Formation

A ReaxFF reactive force field is developed and used for molecular dynamics studies of reactions that occur when diethyl zinc is exposed to a graphene surface that has been functionalized with epoxide groups. From past experiments, it is known that these conditions lead to zinc oxide nanoparticle formation. Molecular dynamics simulations are used to provide atom-level detail into the nanoparticle formation process, including the mechanisms whereby oxygen is abstracted from the graphene surface, thus enabling condensation reactions in which multiple zinc-containing species form zinc oxide fragments and ultimately nanoparticles. Structural properties of the nanoparticles show nonstoichiometric zinc oxide structures with average coordination numbers of 3.6 around each zinc. Time-dependent density functional theory calculations show that the absorption spectra of these clusters are red-shifted by a few tenths of an electronvolt compared to that of a wurtzite crystal structure, representing transitions from oxygen 2p's near the cluster surface to zinc 4s's in the interior.