  We present results on a series of 2D atomistic computer simulations of
amorphous systems subjected to simple shear in the athermal, quasistatic limit.
The athermal quasistatic trajectories are shown to separate into smooth,
reversible elastic branches which are intermittently broken by discrete
catastrophic plastic events. The onset of a typical plastic event is studied
with precision, and it is shown that the mode of the system which is
responsible for the loss of stability has structure in real space which is
consistent with a quadrupolar source acting on an elastic matrix. The plastic
events themselves are shown to be composed of localized shear transformations
which organize into lines of slip which span the length of the simulation cell,
and a mechanism for the organization is discussed. Although within a single
event there are strong spatial correlations in the deformation, we find little
correlation from one event to the next, and these transient lines of slip are
not to be confounded with the persistent regions of localized shear --
so-called "shear bands" -- found in related studies. The slip lines gives rise
to particular scalings with system length of various measures of event size.
Strikingly, data obtained using three differing interaction potentials can be
brought into quantitative agreement after a simple rescaling, emphasizing the
insensitivity of the emergent plastic behavior in these disordered systems to
the precise details of the underlying interactions. The results should be
relevant to understanding plastic deformation in systems such as metallic
glasses well below their glass temperature, soft glassy systems (such as dense
emulsions), or compressed granular materials.
