Ziff–Gulari–Barshad model

The Ziff–Gulari–Barshad (ZGB) model is a simple Monte Carlo method for catalytic reactions of oxidation of carbon monoxide to carbon dioxide on a surface using Monte-Carlo methods which captures correctly the essential dynamics: the phase transition between two poisoned states (either CO2- or O-poisoned) and a steady-state in between. It is named after Robert M. Ziff, Erdogan Gulari, and Yoav Barshad, who published it in 1986.

Model definition
The model consists of three steps: The simplest implementation considers the catalyst as simple square two-dimensional lattice, but one can also consider other kinds of underlying lattices. When a gas-phase molecule touches an empty site, adsorption occurs immediately and the chemical reaction is also instantaneous. Furthermore, assumes that the composition of the gas phase remains constant.
 * Adsorption of the reacting species CO and O2
 * The actual reaction step on the surface: CO + O → CO2
 * Desorption of the products.

Results and other work
The model belongs to the universality class of directed percolation. The model was modified several times.