Yeh et al. proposed that the initiation process of propylene oligomerization entails a series of stoichiometric reactions wherein propylene undergoes several transformations to yield hexadiene and water. This leads to the formation of Ni-hydride species, which subsequently serve as catalytically active species for the oligomerization reactions (Figure ). Remarkably, this initiation mechanism is similar to those investigated for ethylene and butene oligomerization. Therefore, a 25-atom cluster model is chosen as an active species for screening the different transition metal catalysts as shown in Figure .