One major decision in ab initio modelling of AS-ALD is how to treat the substrate. While the chemistry of precursors is clearly modelled with molecular approaches, this is not so clear for molecule-surface interactions. Two major approaches evolved which are both in use in the AS-ALD literature. The general idea of both approaches is illustrated in Fig. .. . This feature can then be modelled by either a cluster or slab approach (c). Based on the selected approach, tuning of computational parameters (d) is the necessary final step.