Density Functional Theory Study Of Hydrogen Adsorption On Ti(0001) Surface

Adsorption energy and work function of hydrogen adsorption/insertion site of Ti (0001) (a 7L-slab) outer-layer/interlayer surface have been calculated based on density functional theory, respectively. It is found that the hcp and fcc sites are the possible adsorption/insertion locations in the Ti (0001)-(1×1)-H system, and the hcp site is more stable than the fcc based on the analyses of the density of states and Mulliken population for Ti (0001) surface of the two kinds of sites, which is attributed to the slight different interaction between H 1 s states and Ti (0001) 3d states. Adsorption energy, density of states, and Mulliken population are further used to discuss the octahedral and tetrahedral at the interlayer surface sites, resulting in 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.Adsorption of H2 molecule on the Ti (0001)-(2×1) surface is studied by density functional theory with generalized gradient approximation (GGA). The parallel and vertical absorption cases are investigated in detail by adsorption energy and electronic structure analysis, we have obtained the three stable configurations of FCC-FCC (the two H atoms adsorption on the two adjacent fcc sites of Ti (0001) surface, respectively), HCP-HCP (the two H atoms adsorption on the two adjacent hcp sites of Ti (0001) 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 final configurations of four vertical adsorption sites are unstable and H2 molecule is very easy to desorption 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 A to 2.3 A for different adsorption configurations due to the strong Ti-H bond forming. The H2 dissociative approach and the final stable configurations formation in parallel adsorption processes are attributed to the quantum mechanics steering effects.