  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.
