Multiple and transforming vibrational identities of atoms in amorphous solids

Identifying the diverse roles of disorderly packed atoms inside an amorphous solid has been a highly pursued but daunting task in glass physics. By analyzing the full-frequency vibrational modes of a model Cu50Zr50 glass, here, we classify the internal atoms into low-, subhigh-, and high-frequency ones that have different tendencies for rearrangements upon excitations. We find that low-frequency atoms are structurally unfavored and tend to aggregate. High-frequency atoms originating from compressed atomic pairs are also mechanically unstable. As yield approaches, shear-transformation rearrangements shift from low-frequency to high-frequency atoms. Subhigh-frequency atoms play the role of stable backbones. Given that atoms can have different identities, multiple identities are observed to overlap in space. Atoms with one vibrational identity often transform to another one, showing different preferences in transformation routes. Our results deepen the understanding of atomic structures for amorphous plasticity beyond the simplified picture of soft vs hard spots.