Free energy change of aggregation of nanoparticles

We used molecular dynamics simulations to calculate the free energy change due to aggregation of MgO nanoparticles in vacuum and examine its dependence on particle size and interparticle orientation. High quality interatomic potentials with a proven track record for simulation of surface and bulk properties, including a representation of electronic polarizability were deployed. The calculations generally predict a free energy barrier to aggregation. However, the free energy barrier to aggregation can be removed by allowing the particles to approach in a crystallographically aligned manner. This implies that aggregation may not be an energetic imperative, but can occur as the result of fluctuations in orientation. Lowering of nanoparticle energy by change in orientation may drive crystal growth via oriented aggregation.