We computationally investigate the hydrogen storage properties of C​ 12 carbyne structure 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 the modeling and simulation Materials Studio program. To account for the dispersion (van der Waals) interactions we also carry out calculations using DFT-D method of Grimme. Dmol​ 3 is used to calculate, total energies, charge density HOMO-LUMO and Mulliken population analysis. Based on these results, up to six H​ 2 molecules per Ca atom can be physisorbed with an average energy of 0.1890 eV (PW91) and 0.3204 (DFT-D) per H​ 2 molecule. This physisorption leads to 6.16 weight percentage (wt%) for the gravimetric hydrogen storage capacity. According to these results, the calcium-decorated carbyne C​ 12 structure is a good candidate for hydrogen storage with application to fuel cells.