  A recent claim of superfluid behaviour of parahydrogen adsorbed inside
armchair carbon nanotubes [M. Rossi and F. Ancilotto, Phys. Rev. B 94, 100502
(2016)] is disproven by means of first principle computer simulations.
Conclusive numerical evidence shows that the low temperature equilibrium
thermodynamic phase of parahydrogen adsorbed inside a (10,10) armchair nanotube
features a crystalline shell adsorbed on the inner surface of the tube, and a
well separated quasi one-dimensional central column showing no evidence of
possible fluid or superfluid behaviour. Rather, the system is quasi-crystalline
and non-superfluid; its physical character is qualitatively identical to that
observed in similar confined settings extensively studied in the past. The
incorrect prediction of superfluidity stems from the erroneous use of an
effective one-dimensional interaction potential that does not describe
parahydrogen at the center of the nanotube.
