From Atomic Scale Ordering to Mesoscale Spatial Patterns in Surface Reactions: A Heterogeneous Coupled Lattice-Gas Simulation Approach

A current challenge in the modeling of surface reaction-diffusion systems is to connect the length scales from a realistic atomistic treatment of local ordering of adsorbed reactants and of reaction kinetics to an "exact" description of mesoscale spatial pattern formation. We discuss a heterogeneous coupled lattice-gas approach which utilizes parallel kinetic Monte Carlo simulations of lattice-gas models to simultaneously determine the local reaction kinetics and diffusive transport properties at various macroscopic "points" distributed across the surface. These simulations are periodically coupled to reflect macroscopic mass transport via surface diffusion. We place particular emphasis on the key issue of correctly describing the associated chemical or collective diffusion flux. This method is general, but it is discussed here only in the context of simple models for the bistable CO oxidation reaction on surfaces, where macroscopic mass transport involves only diffusion of adsorbed CO. Detailed analysis is presented for a canonical model of CO oxidation which incorporates nearest-neighbor exclusion between adsorbed oxygen, leading to superlattice ordering of this reactant. In this model, interactions of adsorbed CO with other adspecies are ignored. This reduces CO surface transport from a many-particle to a single-particle problem, although one with the complexity of "ant-in-the-labyrinth"-type percolative diffusion (the labyrinth being formed by coadsorbed oxygen).