  We couple the recently developed self-learning metabasin escape algorithm,
which enables efficient exploration of the potential energy surface (PES), with
shear deformation to elucidate strain-rate and temperature effects on the shear
transformation zone (STZ) characteristics in two-dimensional amorphous solids.
In doing so, we report a transition in the STZ characteristics that can be
obtained through either increasing the temperature or decreasing the strain
rate. The transition separates regions having two distinct STZ characteristics.
Specifically, at high temperatures and high strain rates, we show that the STZs
have characteristics identical to those that emerge from purely strain-driven,
athermal quasistatic atomistic calculations. At lower temperatures and
experimentally relevant strain rates, we use the newly coupled PES + shear
deformation method to show that the STZs have characteristics identical to
those that emerge from a purely thermally activated state. The specific changes
in STZ characteristics that occur in moving from the strain-driven to thermally
activated STZ regime include a 33% increase in STZ size, faster spatial decay
of the displacement field, a change in the deformation mechanism inside the STZ
from shear to tension, a reduction in the stress needed to nucleate the first
STZ, and finally a notable loss in characteristic quadrupolar symmetry of the
surrounding elastic matrix that has previously been seen in athermal,
quasistatic shear studies of STZs.
