Activation energy of shear transformation zones: a key for understanding rheology of glasses and liquids

Key manifestations of the glassy and liquid states, such as viscous flow and structural relaxation, occur spatial and temporal heterogeneously, within highly localized rare events, termed shear transformation zones. Characterization of these basic entities with respect to thermal activation and mechanical response is vital for understanding the rheology of glasses across length scales. This is achieved in classical molecular dynamics computer simulations on the model glass, CuTi, by determining the activation energy barrier and plastic yield strain of individual shear transformation zones as a function of size and external stress loading. Sizes of approximately equal to 140 atoms are identified to be especially energetically favorable with an activation energy barrier of approximately equal to 0.35 eV. Using these parameters, a rheology model is proposed to quantitatively explain viscosity.