Kinetic Monte Carlo simulation of hydrogen diffusion on tungsten reconstructed (0 0 1) surface

A kinetic Monte Carlo (KMC) algorithm has been developed to study the hydrogen diffusion on tungsten reconstructed (0 0 1) surface in the temperature range 220–300 K. The hydrogen diffusion coefficients predicted by the developed KMC code match the experimental values very well at low hydrogen coverage of a fraction of monolayer. A diffusion coefficient formula as a function of temperature and hydrogen coverage was derived from KMC simulations. Due to the very low probability of hydrogen occupying the long bridge adsorption sites, the rates of hydrogen atom having 3 or 4 neighbors are found to be zero for hydrogen coverage much less than a monolayer, while the rates of hydrogen atom having 0–2 neighbors are linear with respect to the hydrogen coverage. The calculated average rates of hydrogen located at the LB sites are very close to zero for low hydrogen coverage. Hydrogen only starts to occupy the LB sites after almost all SB sites are occupied.