Intriguingly, just as seen for THI transitions during the QM surface-hopping MD simulations (Section 3.1), every THI transition in the classical simulations was immediately preceded by flipping of the stator pucker to that of the target stable form. This is not visible in video mndo-amber.mp4 because of the long time interval between frames, which was chosen to allow viewing of the full rotation process. Therefore, in videos amber-SnearTHI.mp4 and amber-NnearTHI.mp4 of the ESI, we zoom in to animate the details near the THI transition. Figure shows the time series of the key coordinates, i.e. the central torsion angle and puckers, to illustrate the transitions in amber-SnearTHI.mp4. The first event is a sharp change in the pucker of the stator to that of the final stable form, along with a transient backward rotation of the rotor relative to the stator. This is followed by a sharp forward rotation of the rotor to reach the stable form. Meanwhile, the rotor pucker fluctuates rapidly between axial and equatorial until the stator pucker changes, at which point the rotor pucker becomes locked in the equatorial conformation until the rotor rotates to the stable form, at which point the rotor pucker becomes locked in the axial form. Sections 3.3.2 and 3.3.4 provide further details regarding the THI mechanism and kinetics. Figure : Time series of the central torsion angle and puckers before, during, and after a THI transition simulated by classical MD. Forward rotation of the rotor relative to the stator corresponds to a decrease in the central torsion angle. The puckers are defined so that positive/negative rotor pucker mean equatorial/axial, respectively, and positive/negative stator pucker mean the same/opposite pucker as final stable form, respectively. Labels indicate which conformational state (Section 3.3.2) is occupied at each step.