As Goldstein originally hypothesised 2 , the AIMD results for sorbitol show that below T gα structural changes are localised, while temperatures above T gα lead to large-scale conformational rearrangements of the molecules. While this phenomenon is clearly associated with overcoming potential-energy barriers, the origins are slightly more complex, as the barrier heights (and indeed the entire PES) is as dynamic as are the processes themselves. This arises because the PES, which dictates the atomic dynamics and structures, evolves in time as the interactions themselves change, with various factors influencing its structure at any time. For example, inter-molecular anharmonicity, which is responsible for thermal expansion, can lead to a larger accessible free volume of the particles with increasing temperature, which in turn can weaken the inter-molecular interaction strength and thereby lower potential energy barriers for conformational rearrangements.