Figure 2:

A schematic diagram of the RET approach. The new configuration R2** on replica 1 has after re-scaling of velocities the same total energy as the old configuration R1*. While evolving to the state R2^# potential and kinetic energies interconvert, symbolically noted by the shift in color. In a similar way the configurations R1** and R2* on replica 2 have the same energy, and R1** evolves to R1^#.