  The nucleation of cavities in a homogenous polymer under tensile strain is
investigated in a coarse-grained molecular dynamics simulation. In order to
establish a causal relation between local microstructure and the onset of
cavitation, a detailed analysis of some local properties is presented. In
contrast to common assumptions, the nucleation of a cavity is neither
correlated to a local loss of density nor, to the stress at the atomic scale
and nor to the chain ends density in the undeformed state. Instead, a cavity in
glassy polymers nucleates in regions that display a low bulk elastic modulus.
This criterion allows one to predict the cavity position before the cavitation
occurs. Even if the localization of a cavity is not directly predictable from
the initial configuration, the elastically weak zones identified in the initial
state emerge as favorite spots for cavity formation.
