First-principles calculations of hydrogen molecule adsorption on Ti (0 0 0 1)-(2 × 1) surface

Adsorption of H2 molecule on the Ti (0 0 0 1)-(2 × 1) surface was studied by density functional theory with generalized gradient approximation (GGA). The parallel and vertical absorption cases were investigated in detail by adsorption energy and electronic structure analysis, we obtained three stable configurations of FCC–FCC (the two H atoms adsorption on the two adjacent fcc sites of Ti (0 0 0 1) surface, respectively), HCP–HCP (the two H atoms adsorption on the two adjacent hcp sites of Ti (0 0 0 1) surface, respectively) and FCC–HCP (the one H atom adsorption on the fcc site and the other adsorption on the near hcp site) based on the six different parallel adsorption sites after the H2 molecule dissociates. However, all the end configurations of four vertical adsorption sites were unstable, H2 molecule was very easy to desorb from Ti surface. The H–H bond breaking and Ti–H bond forming result from the H2 molecule dissociation. H–H bond breaking length ranges from 1.9 Å to 2.3 Å for different adsorption configurations due to the strong Ti–H bond forming. The H2 dissociative approach and the end stable configurations formation in parallel adsorption processes are attributed to the quantum mechanics steering effects.