Modeling generation and growth of iron oxide nanoparticles from representative precursors through ReaxFF molecular dynamics.

Detailed dynamical characterization of the mechanisms responsible for the formation and growth of iron oxide nanoparticles remains a significant challenge not only for experimental techniques but also for theoretical methodologies due to the nanoparticle size, long simulation times, and complexity of the environments. In this work, we have designed a fast computational protocol based on atomistic reactive molecular dynamics, which is capable of simulating the whole synthetic and proliferation process of the nanoparticles (greater than 10 nm) in a homogeneous medium from organometallic precursors. We have defined appropriate growth accelerating strategies based on the observed reactions, which consisted of the formation of Fe-O-Fe bridges, linking separate precursors, and Fe˙ and FeO˙ radicals. This reduced drastically the computational time allowing the simulation of NPs made of thousands of atoms (full nanometric range). We have identified the most probable reaction environments and summarized them under two distinct conditions: reductive and oxidative. The first one leads to the formation of nanoparticles with FeO stoichiometry typical of wustite, whereas the second one stabilizes stoichiometries between Fe