Shear transformation distribution and activation in glasses at the atomic scale.

We characterize shear transformations (STs) at the atomic scale in a model of amorphous silicon using a mapping on Eshelby inclusions. We investigate the effect of pressure, glass relaxation, as well as damage on the ST characteristics. We show that the characteristic ST effective volume, γ_{0}V_{0}, product of the ST plastic shear strain γ_{0} and volume V_{0}, does not depend significantly on an applied pressure but increases with accumulated plastic deformation from about 10Å^{3} in the pseudoelastic regime to about 60Å^{3} once plastic flow sets in. Furthermore, by using nudged elastic band calculations, we measure the energy barrier against ST activation. Analyzing different paths leading to either an isolated ST or an avalanche, we show that the barrier is systematically controlled by the first ST with an activation volume equal to the effective volume of the ST at the activated state, which represents only a fraction of the complete ST volume. The activation volume is also found smaller for avalanches, presumably because of accumulated local damage. This work provides essential information to build reliable mesoscale models of plasticity.