Study of hydrogen adsorption on the Ti (0001)-(1×1) surface by density functional theory

We calculated adsorption energy, work function of different hydrogen adsorption and insertion sites of Ti (0 0 0 1) (a 7L-slab) outer-layer and interlayer surface based on density functional theory, respectively. It is found that the hcp and fcc sites are the most possible adsorption/insertion locations in the Ti (0 0 0 1)-(1 × 1)–H system. The hcp site is more stable than the fcc based on the analyses of the density of states and Mulliken population for Ti (0 0 0 1) surface of the two kinds of sites, which is attributed to the slight different interaction between H 1s states and Ti (0 0 0 1) 3d states. Adsorption energy, density of states, and Mulliken population are further used to discuss the octahedral and tetrahedral at the interlayer surface sites. It is found that the adsorption energy at the octahedral or the tetrahedral sites between the 2nd and the 3rd layers is bigger than that between the 1st and the 2nd, or the 3rd and the 4th layers. Furthermore, hydrogen insertion inside the titanium super-cell (1 × 1 × 7) structure is also discussed.