Atomic nonaffinity as structural indicator of protocol-dependent plasticity in amorphous solids

Structural heterogeneity of amorphous solids is intimately connected to their mechanical behavior. Based on a perturbation analysis of the potential energy landscape, we derive a new structural indicator, termed the atomic nonaffinity, which qualifies the contribution of an individual atom to the total nonaffine modulus. We find that the atomic nonaffinity can efficiently characterize the locations of shear transformation zones (STZ) as well as their protocol-dependent response arising from their orientational nature. We quantitatively show that plastic events tend to happen in the STZs whose softest shear directions are close to the loading shear direction. These results provide new insight towards understanding and characterizing the plastic response of amorphous solids.