The interactions between atoms is treated with classical mechanics. Thus, the electrons are not considered explicitly but in an indirect fashion. To carry out a classical MD computation, a force field is required. This is a set of parameters which describes the interactions between the atoms. Typically, it consists of bonded parameters (potential energy functions for distance, angle and dihedral angle changes) and non-bonded parameters (electrostatic and van der Waals forces). For each atomic species in the system (atom type and connectivity, e.g., the C atom in C2H6 has a different parameter than in C2H2), and for every resulting pair of atoms, parameters have to be provided. As one can imagine, this leads to huge parameter sets for systems relevant for AS-ALD. Moreover, deriving these parameter sets and evaluating their accuracy is far from trivial. However, the choice of the specific force field is crucial for the reliability of the computational results and has to be tailored to the system. Choosing the wrong force field gives bogus results. The main advantage of classical MD is that rather large systems (1000s of atoms) and timescales (ns, cuttingedge computations even µs) can be treated. The major drawback of this approach for AS-ALD is that connectivity changes (bond making, bond breaking) usually cannot be described since the approach relies on the connectivity of the atomic species. Reactive force fields try to remedy this issue but are still hardly used for surface chemistry. Also in this approach, the combination of atoms modelled has to be incorporated in the parametrization to make it applicable.