Using density functional theory together with dispersion correction, we optimize geometries and calculate encapsulation energies, charge transfer, and electronic structures of a one-dimensional ThCl6 chain encapsulated within single-walled carbon nanotubes. The optimized structures are in agreement with the experimentally observed single chain of ThCl6 confined within nanotubes. Exoergic encapsulation energies indicate that the chain is thermodynamically stable inside the nanotubes. The inclusion of dispersion correction enhanced the encapsulation. The strong nature of encapsulation is further confirmed by the charge transfer between the nanotubes and the chain. The one-dimensional chain structure exhibits a small increase (0.20 eV) in the bandgap compared to that of bulk ThCl4. The metallic (15,0) tube becomes a narrow gap semiconductor upon encapsulation, while the semiconducting nature of the (17,0) tube is still kept despite the reduction in the bandgap.