Molecular dynamics study of tracer diffusion of argon adsorbed on amorphous surfaces

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Abstract
An isokinetic molecular dynamics simulation of argon adsorbed on several model amorphous surfaces of titanium dioxide is carried out. The solid is represented by the Bernal Model in which the surface is taken to be the exposed face of a dense random packing of oxide ions. This surface is roughened by deleting varying numbers of oxides at random from the outer layer of the solid. Surfacediffusion in the limit of very low coverage (tracer diffusion) is evaluated by following the dynamics of noninteracting single adatoms. The diffusion coefficient in the zero‐density limit is calculated from velocity autocorrelation functions for adatoms at several temperatures ranging from 85 to 300 K. The temperature dependence of the diffusion constants obtained in this way shows nearly Arrhenius behavior in this temperature range. It is shown that surface roughening at the atomic scale give rise to a higher apparent activation energy for diffusion. A statistical characterization of the adsorptive field through distributions of local maxima and minima in the adsorption energy surface along the diffusion paths was performed in order to relate the surfacediffusion of monatomic species on amorphous surfaces to the recently proposed Dual Site‐Bond Description of Heterogeneous Surfaces (DSBD). Independent evidence supporting the theoretical hypothesis of the DSBD is also obtained.