First, we analyze the polymerization of acetylene, which corresponds to the formation of soot precursor -PAH molecules. The reaction pathway from acetylene to benzene is shown in Fig. . The polymerization starts with the collision and addition reaction between two acetylene molecules at 1.5 ps to generate an HC≡CH-CH≡CH molecule, which further grows into a long chain molecule (e.g., HC≡CH-CH≡CH-CH≡CH) with the addition of another acetylene molecule at 3.6 ps. This species further forms a benzene via an isomerization reaction at 6.4 ps, and this pathway is consistent with a previous work . Figure shows the pathway from benzene to the 2 nd aromatic ring. The hydrogen atom in benzene is abstracted by other radicals to generate a reactive site. Then, a CCH radical attacks the reactive site at 11.1 ps to form a benzene with an acetylene chain, and this structure is expected to be stable at flame temperatures . At 12.4 ps, the second addition reaction occurs near the first acetylene chain and forms the 2 nd aromatic ring after long isomerization (~5.1 ps). In Fig. , we also observe the formation of a large PAH with four aromatic rings at 101.7 ps, which follows similar acetylene addition and isomerization pathways. The dynamic evolution of the main species during the polymerization process is shown in Fig. . Since there are a large number of isomers for CxHy species, the products are grouped by their carbon atom numbers. It shows that the C2 group is rapidly consumed within the first 10 ps. The insert in Fig. illustrates the main species of each group, which is extracted from MD trajectories using the ReacNetGenerator package . The main composition includes acetylene, but there are also hydrogen transfer and elimination reactions to produce CCH2 and CCH radicals. C4 and C6 groups are the main products of C2 polymerization in the first 20 ps. In Fig. , the C7-10 group represents the growth of the 2 nd ring, which reaches a maximum at ~ 30 ps and starts to decrease. Groups with larger carbon atom numbers follow the same trends but at a slow rate. For example, the time needed to reach the maximum number of molecules was ~40 ps for the C11-15 group and ~200 ps for the C15-20 group. In the above simulation, the growth of large PAHs from small acetylene is observed, proving the feasibility of studying soot formation using our NN model.