Simulating the morphology of clusters of polycyclic aromatic hydrocarbons: The influence of the intermolecular potential

Stacking of polycyclic aromatic hydrocarbons is recognized as a key step in particle inception process in hydrocarbon-rich combustion. A conclusive description of the process is not reached, indeed uncertainties remain on the molecules involved in the process and on their intermolecular potential function. A study of the evolution of coronene (C24H12) at a temperature of 500 K and additional analysis on the morphology of particles obtained have been performed in this paper by using a molecular dynamics approach. Four intermolecular potentials, which differ for their function forms and magnitudes of the interaction involved, have been tested in order to outline the difference in cluster formation and morphology. The cluster formation is strongly dependent on the magnitude of potential interaction, while it is weakly dependent on the differences in the repulsive branch of the potential function. Potentials which have a similar interaction intensity but have two different repulsive branches, exhibit very similar percentage of clustered molecules, number of cluster formed and cluster mean sizes. The electrostatic interactions do not remarkably affect the cluster formation propensity, but different morphologies are found. The electrostatic term increases the disorder in the structure of the formed clusters for all the investigated potentials, due to an increased number of molecules not arranged in parallel planes. The use of a systematic approach to analyze the internal structure and shape of the formed cluster allowed to have a better comparison between the potentials and their capability to reproduce realistic configurations.