where 𝐺 ,,>.?@ and 𝐺 ,,AB./9 are the total free energies of the (𝑛)-long and (𝑛 -𝑘)-short polymer models, respectively. In Eq. ( ) 𝑛 is the number of HCN in the long oligomer model, and 𝑘 is the number of HCN in a monomer unit. The sizes of our oligomer models were chosen to have at least 4 repeating polymer units, and 𝑛 is always near 20. Each polymer model was capped by a cyanide group in one end and a hydrogen atom in the other end.