Trajectories were taken each 10 steps. To clarify the physical meaning of our proposed method, we compared phase-field and MD simulations. . This event can be attributed to that the vibration of atoms often exceeds the energetic barrier between two states due to momentum. In regard to phase-field simulation, a dihedral angle also gradually grew and stabilized around 90 • . However, the conformation switching was not observed in time progress. This indicates that effect of momentum to the dynamics is abandoned in the replacement of vibration to a density. This should be paid attention in the interpretation of simulation results.