We computationally investigate the hydrogen storage properties of carbyne C-10-ring structure on either D-nh or D-(n/2)h symmetry decorated with calcium (Ca) atoms adsorbed on its outer surface. The calculations are carried out on DFT-GGA-PW91 and DFT-GGA-PBE levels of theory as implemented in Biovia Materials Studio modeling and simulation software. To account for van der Waals interactions we also carried out calculations using DFT-D method of Grimme. Dmol(3) is used to calculate total energies, HOMO-LUMO electronic charge density, Mulliken population analysis, and electrostatic potential fitting charges (ESP). Based on these results: i) the average binding energy of Ca atom doping to C-10-ring is similar to 2.3 eV (PW91) and similar to 2.1 eV (PBE). ii) Up to seven H-2 molecules per Ca atom can be physically adsorbed with an average energy of similar to 0.2 eV per H-2 molecule. iii) This physisorption leads to 8.09 wt percentage (wt. %) for the gravimetric storage capacity. According to these results, calcium-decorated carbyne C-10-ring structure is excellent candidate for hydrogen storage at ambient conditions with application to fuel cells. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.