What's KMC All About And Why Bother

If you are wondering "What can Kinetic Monte Carlo (KMC) do for me?" this article is for you. It is intended as a discussion more than a tutorial in the strict sense, but with a (hopefully) clear learning aspect. Thus, we will highlight the benefits of KMC compared to simpler approaches, such as mean-field (micro-kinetic or phenomenological) models, taking as an example a prototypical system: the CO oxidation reaction. Of course, the main ideas behind this discussion hold true for more complicated reactions as well.

So the net reaction we will discuss is:

CO + ½O2 → CO2

When this happens on the surface of a catalyst (e.g. the (111) facet of a Pd nano-crystal) the reaction could proceed via the following three elementary steps:

CO + * ↔ CO* (reversible adsorption of CO on an empty catalytic site)
O2 + 2* ↔ 2O* (reversible dissociative adsorption of O2 on two neighboring empty catalytic sites)
CO* + O* → CO2 + 2* (irreversible reaction between adsorbed CO and O yielding gas CO2)

In the notation we just used and will adopt throughout, * denotes an empty site, whereas A* an adsorbate (bound species A).