  We systematically investigate the relationships between structural and
electronic effects of finite size zigzag or armchair carbon nanotubes of
various diameters and lengths, starting from a molecular template of varying
shape and diameter, i.e. cyclic oligoacene or oligophenacene molecules, and
disclosing how adding layers and/or end-caps (i.e. hemi-fullerenes) can modify
their (poly)radicaloid nature. We mostly used tight-binding and
finite-temperature density-based methods, the former providing a simple but
intuitive picture about their electronic structure, and the latter dealing
effectively with strong correlation effects by relying on a fractional
occupation number weighted electron density (\rho FOD ), with additional RAS-SF
calculations backing up the latter results. We also explore how minor
structural modifications of nanotube end-caps might influence the results,
showing that topology, together with the chemical nature of the systems, is
pivotal for the understanding of the electronic properties of these and other
related systems.
