General potential-energy function for H/Ni and dynamics calculations of surface diffusion, bulk diffusion, subsurface-to-surface transport, and absorption

We present a potential-energy function for H interacting with bulk metallic Ni. The potential is parametrized to be accurate both for H adsorbed on Ni surfaces and for H absorbed at interior sites. The function introduces a nonlocal density dependence into the embedded-atom method formalism. We show that the function provides dramatic improvement over the best previous embedded-atom potential function for this system, and that it gives good agreement with all available structural and energetic data characterizing stationary points on the low-index surface planes [(100), (111), and (110)] and in the interior. It also yields good agreement with experiment for most diffusion coefficients and activation energies for surface and interior diffusion. We examine the dynamics of three diffusion processes: H diffusing on the (100) and (111) crystal faces, and H migrating in the interior, for the latter of which we analyze the reaction path and predict coefficients for H diffusion between adjacent interior octahedral vacancies. We also examine two other processes: H hopping from the threefold (111) surface binding site to an octahedral vacancy immediately beneath the (111) surface plane to (absorption), and the reverse process (deabsorption). We also calculate the binding energy and frequencies for H adsorbed on the pseudothreefold site of the Ni(110) surface, and we find them to be in good agreement with experiment and a considerable improvement over previous versions of the potential function. Our potential-energy function should be useful for simulations of a variety of processes that are difficult to study experimentally, such as surface diffusion in the presence of steps and kinks, site-to-site movement of H immediately beneath a surface plane of Ni, or bulk transport across a grain boundary.