QUANTUM DIFFUSION OF HYDROGEN AND DEUTERIUM ON NICKEL(100)

The diffusion constants of hydrogen and deuterium at low temperature a re calculated using the surrogate Hamiltonian method and an embedded a tom potential. A comparison with previous experimental and theoretical results is made. A crossover to temperature-independent tunneling occ urs at 69 K for hydrogen and at 46 K for deuterium. An inverse isotope effect at intermediate temperatures is found, consistent with experim ent. Deviations are found at low temperature where a large isotope eff ect is calculated. (C) 1998 Published by Elsevier Science B.V. All rig hts reserved.