This study is divided into two inter-related parts. The first part (part A) is to investigate how benzene, indene and naphthalene are produced from small hydrocarbon reactants. The second part (part B) is to simulate the growth of PAHs produced from acetylene and small aromatic rings produced in part A. Part A is important since the formation of the first sixmembered aromatic ring is a critical step in the growth process of PAHs . To increase sampling efficiency and save computational cost, part B directly uses the aromatic species produced in part A as reactants. The following provides detailed results from the simulations in these two parts.