We next investigate the hydrogenation of periodic 10-atom C chains. In Section , as explained in detail, the hydrogenation process was done by adding one and two-side H atom to each C atom in the chain. Our geometry analysis showed the predicted d C-C bonds are underestimated by the ANN potential. Here, we compare the hydrogenation energy (E hydro ) of the chain which represents the energy change associated with adding H atoms to C. E hydro was calculated as the total energy difference between the hydrogenated (saturated) and non-hydrogenated (pristine) states of the C-chain: