Onset of fragment formation in periodic expanding systems.

Abstract

The problem of the time evolution of the process of fragment formation is investigated in the framework of expanding periodic systems. We focus on the fragmentation of small (100 constituents) systems. We use a molecular-dynamics method that simulates the behavior of condensed matter under homogeneous adiabatic expansion. Fragment formation is studied using a generalized version of the early cluster formation model (GECFM) which searches for the most bound density fluctuations in phase space. We show that the asymptotic fragment spectra is early realized in phase space not only for the total multiplicity but also for the populations of different mass ranges. In order to map the evolution of the system on the phase diagram of the small cell periodic one, its equation of state is calculated. It is shown that the fragmentation of the system cannot be unambiguously related to spinodal decomposition or nucleation processes. \textcopyright{} 1996 The American Physical Society.