Lattice distortions around frozen and mobile hydrogen in niobium: A molecular-dynamics study

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Abstract
We have studied the hydrogen-induced lattice distortions in niobium using the molecular-dynamics simulation technique. A two-exponential interatomic potential for the H-Nb interaction is proposed, based on recent first-principles calculations for the H/Nb system. The quasielastic diffuse scattering cross section is determined and compared with neutron scattering data. The importance of the hydrogen motion is elucidated by comparing results from dynamic simulations with static defect models and we find that the usual way of introducing the thermal motion of the atoms through a Debye-Waller factor gives a rather imprecise description of the q dependence of the scattering cross section. We also find some evidence that the actual time scale for the hydrogen motion influences the shape of the scattering function at high temperatures (450 K) while at lower temperatures (300 K) this effect is of minor importance. When comparing with the experimental results we find agreement for the q dependence but not for the absolute intensities. © 1996 The American Physical Society.