It is reported that the conical intersection (CI) between the |g⟩ and |e⟩ states plays an important role in the photoisomerization process of the azomethane molecule. Thus, we optimized the molecular geometry of the CI between the ground state and the first excited state (see the inset geometry with "CI" label in Fig. ) using geometry optimization method proposed by Yarkony and co-worker, 58 as implemented in the Molpro 2015 package. The CI-optimized geometry is obtained at the SA-2-CAS(6,4) level of theory. We also obtained the optimized geometries of both cis and trans isomers in the ground electronic state, at the level of DFT using B3LYP/6-31G*. The entire isomerization reaction path was generated by linear interpolation in internal coordinates from the CI geometry to both the cis isomer and the trans isomer. We generated a total of 60 of the geometries along the reaction path, and they are not further optimized (as such, they are just rigid interpolation away from the CI point to the cis and trans isomers). These geometries are used to plot the PESs in Fig. , as well as used for visualizing the molecular dipoles in Fig. , and for polariton PESs and gradients in Fig. .