  These are lecture notes of a course that I gave to people doing research for
their Ph.D. thesis in theoretical chemistry or spectroscopy. The course was
given on December 9-13, 2002, in Han-sur-Lesse, Belgium.
  The lecture notes start with the lattice-gas model that is used to describe
the reactions on a surface. I derive a Master Equation, which gives the
evolution of this model. The Master Equation contains transition probabilities
(or rate constants) for the reactions. I show how these transition
probabilities can be obtained from quantum chemical calculations or from
experiments. The Master Equation can be solved using several different Monte
Carlo algorithms. I derive these algorithms, and show what their advantages and
drawbacks are. I use a number of simple reaction systems to illustrate various
possibilities that one has when modeling reactions on surfaces. Finally, I
discuss more realistic systems to show what kind of kinetic phenomena can be
studied with Monte Carlo simulations.
