The surface can be modelled by cutting out a small cluster containing the reactive site (Fig. .). The adsorbate then interacts with this active site in the computations. This approach is computationally very efficient and does not need large HPC resources. Furthermore, it allowsin principlethe usage of more accurate methods than DFT (e.g., MP2, CCSD(T)) since computational codes of molecular chemistry can be used. In AS-ALD modelling, it is mainly used to compute adsorption structures of precursors and SMIs. The pioneering modelling of ALD chemistry by Musgrave et al. had been started by using this modelling approach. They established the cluster approach to model the silicon surface (Si9H12)