  Plastic flow in amorphous solids is known to be carried by localized shear
transformations (STs) which have been proposed to preferentially initiate from
some defect units in the structure, akin to dislocations and point defects in
crystalline solids. Despite the central role of STs in the mechanical
deformation of metallic glasses (MGs), our knowledge of their characteristics
has so far been limited to hypothetical models, based on computer simulations
using unreleastically high cooling rates. Using combined molecular dynamics
(MD) and Monte Carlo (MC) simulations, here we have succeeded in solidifying a
metallic liquid at an effective cooling rate as slow as 500 K/s to approach
that typical in experiments for producing bulk MGs. Exploiting this realistic
MG model, we find that STs do not arise from signature structural defects that
can be recognized a priori. Upon yielding, only about 2% of the total atoms
participate in STs, each event involving as few as ~10 atoms. These findings
rectify the unrealistically high content of liquid-like regions retained in
MD-produced glass structures, which has rendered the MG model artificially
ductile and under-predicted the sample-wide shear modulus by at least ~20%
(with respect to that of experimental BMGs). Our finding sheds light on the
scope of intrinsic structural inhomogeneity as well as the indeterministic
aspect of the ST emergence under mechanical loading.
