<p>In this investigation, Ca deposited B₁₆ structure as a promising hydrogen storage improver system has been evaluated via density functional theory (DFT) approach. The Ca@B₁₆ and 2Ca@B₁₆ structures were designed and their adsorption capacities for hydrogen molecules were studied. The Ca@B₁₆ system can absorb up to four hydrogen molecules while 2Ca@B₁₆ can adsorb maximum six hydrogen molecules. Due to the fact that hydrogen adsorption depends on the polarization quality of Ca-B bond of the studied surface, the H₂ molecules were adsorbed on the Ca atom(s) of the cluster. Our calculations revealed that the hydrogen gravimetric uptake in the 2Ca@B₁₆ is about 4.7 wt.% with average adsorption energy per hydrogen molecule (&lt; E_ads &gt;) of − 1.433 to − 2.518&#xa0;kcal&#xa0;mol⁻¹. As a result, by manipulating the 2Ca@B₁₆ content, the hydrogen storage capacity can be increased and this small cage may be a candidate material for promoting hydrogen storage process. </p> Graphical abstract <p></p>