Monte Carlo algorithms for complex surface reaction mechanisms: Efficiencyand accuracy

A continuous-time Monte Carlo (CTMC) algorithm with lists of neighbors and local update (tree-type architecture) for simulating the dynamics and stati onary pattern formation of complex surface reaction mechanisms is discussed . Two additional CTMC algorithms, often used in the literature, are also pr esented. The computational efficiency of these CTMC algorithms is compared to a null-event algorithm for the CO oxidation on a Pt(100) surface by dire ct numerical simulations. Furthermore, we have derived simple formulas for the real time advanced using the null-event algorithm and the CTMC with loc al update algorithm for the infinitely fast and finite CO oxidation kinetic s as well as a unimolecular surface reaction. We have found that the propos ed CTMC algorithm with classes and local update can be much faster than the traditional null-event algorithms by orders of magnitude, when stiffness o ccurs (rare event dynamics). In addition, we address the computational accu racy of Monte Carlo algorithms, due to limited resolution caused by finite lattice sizes, for key intermediate species in a complex reaction mechanism . It is shown that Surface concentrations below the resolution of the latti ce and corresponding reaction rates can accurately be calculated through th e use of a time-weighted average of reaction rates. (C) 2001 Academic Press .