Delocalization transition of a small number of particles in a box with periodic boundary conditions

We perform molecular dynamics simulation of a small number of particles in a box with periodic boundary conditions from a viewpoint of chaotic dynamical systems. There is a transition at a critical energy Ec that each particle is confined in each unit cell for E< Ec, and the chaotic diffusion occurs for E> Ec. We find an anomalous behavior of the jump frequency above the critical energy in a two-particle system, which is related with the infinitely alternating stability change of the straight motion passing through a saddle point. We find simultaneous jump motions just above the critical energy in a four-particle system and 16-particle system, which is also related with the motion passing through the saddle point.