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 met allic Ni. The potential is parametrized to be accurate both for H adso rbed on Ni surfaces and for H absorbed at interior sites. The function introduces a nonlocal density dependence into the embedded-atom metho d formalism. We show that the function provides dramatic improvement o ver the best previous embedded-atom potential function for this system , and that it gives good agreement with all available structural and e nergetic data characterizing stationary points on the few-index surfac e planes [(100), (111), and (110)] and in the interior. It also yields good agreement with experiment for most diffusion coefficients and ac tivation energies for surface and interior diffusion. We examine the d ynamics of three diffusion processes: H diffusing on the (100) and (11 1) crystal faces, and H migrating in the interior, for the latter of w hich we analyze the reaction path and predict coefficients for H diffu sion between adjacent interior octahedral vacancies. We also examine t wo other processes: H hopping from the threefold (111) surface binding site to an octahedral vacancy immediately beneath the (111) surface p lane to (absorption), and the reverse process (deabsorption). We also calculate the binding energy and frequencies for H adsorbed on the pse udothreefold site of the Ni(110) surface, and we find them to be in go od agreement with experiment and a considerable improvement over previ ous versions of the potential function. Our potential-energy function should be useful for simulations of a variety of processes that are di fficult to study experimentally, such as surface diffusion in the pres ence of steps and kinks, site-to-site movement of H immediately beneat h a surface plane of Ni, or bulk transport across a grain boundary.