A theoretical study on the mechanisms of formation of primal carbon clusters and nanoparticles in space

We present a computational study of assembling carbon clusters and nanophases in space from carbon aggregations. Geometry optimizations and Density-functional-based tight-binding (SCC-DFTB) dynamics methods are employed to predict carbon clusters, their time evolution, and their stability. The initial density of the aggregates is found to be of primary importance for the structural properties of the clusters. Aggregates with sufficiently low initial density yield clusters with approximately equal prevalence of sp and sp2 hybridized states and almost missing sp3 ones. The increase in the initial density results in sp2-dominant molecules that resemble the carbon skeleton of polycyclic aromatic hydrocarbons (PAHs). Larger initial aggregations with tetrahedral interatomic orientation result in sp2-dominant multi-dimensional polymers. Such materials are highly porous and resemble axially bound nanotubes. Some resultant clusters resemble fullerene building blocks. Spheroid nanoparticles resembling improper fullerenes are predicted by metadynamics, aimed at inter-fragment coupling reactions. One such structure has the lowest binding energy per atom among the studied molecules. All zero-dimensional forms, obtained by the simulations, conform to the experimentally detected types of molecules in space. The theoretical IR spectrum of the clusters closely resembles that of fullerene C70 and therefore such imperfect structures may be mistaken for known fullerenes in experimental infrared (IR) telescope studies.