Monte-Carlo simulation of diffusion in a two barriers system

Surface diffusion is studied in a two barrier system, i.e. a system with two different activation energies. The dynamic and thermodynamic properties of the system of interacting ad-atoms on an fcc(1 1 1) surface are studied using Monte-Carlo simulations, the Bortz–Kalos–Lebowitz algorithm and the Metropolis algorithm. The results are compared with our previous analytical calculations in the same system. Numerical results fit well to the analytical results for high temperatures. At low temperatures, contrary to previous analytical calculation (based on quasi-chemical approximation), we observe a sharp local minimum at a coverage Θ =0.5 in the case with repulsive interaction and a large difference between activation energies. The Monte-Carlo simulations result in a higher occupation of deep sites, formation of an ordered phase and in lower diffusion coefficient in comparison with the analytical results.