Anisotropic local stress and particle hopping in a deeply supercooled liquid.

The origin of the microscopic motions that lead to stress relaxation in deeply supercooled liquid remains unclear. We show that in such a liquid the stress relaxation is locally anisotropic which can serve as the driving force for the hopping of the system on its free energy surface. However, not all hoppings are equally effective in relaxing the local stress, suggesting that diffusion can decouple from viscosity even at the local level. On the other hand, orientational relaxation is found to be always coupled to stress relaxation.