A simulation model for hydrogen in palladium. I. Single-particle dynamics

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Abstract
The author constructs and examines the properties of a simulation model for Pd:H. The metal-metal potential is based on the polynomial model of van Heugten (1979), and the metal-hydrogen potential is represented by a parameterised exponential form. The molecular dynamics calculations show that the temperature-dependent tracer diffusion coefficient of hydrogen is in semi-quantitative agreement with experiment, and that the residence site of the hydrogens is the octahedral position, as required by diffraction measurements. Diffusion occurs by jumps between these sites, but the jumps are not uncorrelated, so that the Chudley-Elliott model does not provide a satisfactory description. The relation between the model and the real system is discussed with particular reference to the correlation of jumps, and a physical mechanism which might reduce this correlation is suggested.