Rotational correlation functions and apparently enhanced translational diffusion in a free-energy landscape model for the α relaxation in glass-forming liquids

We explore a simple model for supercooled liquids in which reorientational and translational motions are inherently coupled to the structural relaxation. Several controversial aspects of the molecular motion in glass-forming materials are naturally resolved within the framework of our model. These include the geometry of the molecular reorientations as well as the apparent enhancement of translational diffusion. The breakdown of the Stokes-Einstein relation is thus explained without assuming the existence of local diffusion coefficients.