The mechanisms of single-dimer self-diffusion on the (111), (001) and (110) surfaces of face-centered cubic iridium were investigated. A realistic many-body potential, the Rosato-Guillope-Legrand model potential, was used which involved empirical fittings of bulk properties of the solid. On the (001) and (110) surfaces, evidence of atomic diffusion by exchange mechanisms of the dimer atoms with substrate atoms were found. This was in good agreement with field-ion microscopic observations. In addition, a preliminary investigation of the mechanisms of self-diffusion of iridium trimers on the (110) plane were carried out. An approach to calculating diffusivities, both transport as well as equilibrium, was presented. The dual control volume grand canonical molecular dynamics method used two local control volumes for chemical potential control via particle creation/destruction as in grand canonical Monte Carlo simulations. The control volumes were inserted into a standard NVT molecular dynamics simulation yielding a simulation with stochastic chemical potential control that may be thought of as a hybrid approach. Geometrical control of the chemical potential permitted a steady-state chemical potential gradient to be established in the system. By measuring the density profile and flux, Fick’s law was used to determine the diffusivity. An example calculation was presented for a simple Lennard-Jones system.

Molecular-Dynamics Study of Self-Diffusion: Iridium Dimers on Iridium Surfaces. Shiang, K.D., Tsong, T.T.: Physical Review B, 1994, 49[11], 7670-8

Table 15

Diffusion and self-diffusion in molten K-Cs alloys