Based on density functional theory: Reactions mechanism of Tan (n = 2–5) clusters and water molecules

[Display omitted] •The most stable adsorption structure of tantalum clusters.•Tan + H2O (n = 2–5) reaction belongs to the exothermic reaction.•The hydrogen evolution reaction of Ta4 + H2O releases −2.45 eV.•The Ta2 + H2O and Ta5 + H2O hydrogen evolution reaction has three transition states.•The reaction of Ta3 clusters with water molecules leads to complete hydrogen desorption. The reaction paths of water molecules and Tan (n = 2–5) clusters were predicted by density functional theory calculations. The lowest energy structures of Tan@H2O (n = 2–5) clusters were found and their complexes were structurally optimized at the adsorption sites of clusters. Meanwhile, all reactants, products and transition states were found by structural optimization and frequency analysis. Based on NBO and IRI analysis, Water molecules adsorbed on the surface of tantalum clusters can all form a Ta-O bond. From the dissociation channel, the Tan (n = 2–5) clusters can extract H2 from water molecules and the whole reaction process is exothermic, these results help to design practical hydrogen generation schemes by these reactions.