As outlined in more detail above (section 1.4.4), there are four main mechanisms that lead to loss of selectivity in inhibitor-based AS-ALD: (i) penetration or (ii) decomposition of the inhibitor layer by the precursor, (iii) thermal decomposition of the inhibitors (including desorption) and (iv) overgrowth by nucleation on top of the inhibitor layer or growth over the interface to the GS (termed 'mushrooming') . It is easily seen that the mechanisms (except iii) are tightly connected to the structure and chemical reactivity of the precursor. The general requirement for a good precursor are thus: it readily reacts with the GS but does not lift selectivity by decomposition, penetration or overgrowth of the inhibitor layer on the NGS. How have computational studies helped to reveal these factors?