Subsurface bonding of hydrogen in niobium: A molecular-dynamics study

Binding energy of hydrogen in a (100) niobium slab is investigated through molecular-dynamics simulations. We introduce a hydrogen-niobium interaction potential that contains an attractive as well as a repulsive part, which is valid for surface-diffusion calculations. Simulations for high and low temperatures (compared with ${\theta }_{\mathrm{Debye}}$) are presented. For the former case, we found that the hydrogen diffuses in the slab with a diffusion coefficient in agreement with experiment, and in most cases it is trapped inside the slab for $T<~900\mathrm{K}.$ Close to room temperature, there is an enhancement of the hydrogen binding energy, which causes self-trapping close to the surface.