  Usually, supercooled liquids and glasses are thermodynamically unstable
against crystallization. Classical nucleation theory (CNT) has been used to
describe the crystallization dynamics of supercooled liquids. However, recent
studies on overcompressed hard spheres show that their crystallization dynamics
are intermittent and mediated by avalanche-like rearrangements of particles,
which largely differ from the CNT. These observations suggest that the
crystallization times of deeply supercooled liquids or glasses cannot be
described by the CNT, but this point has not yet been studied in detail. In
this paper, we use molecular dynamics simulations to study the crystallization
dynamics of soft spheres just after an instantaneous quench. We show that
although the equilibrium relaxation time increases in a super-Arrhenius manner
with decreasing temperature, the crystallization time shows an Arrhenius
temperature dependence at very low temperatures. This is contrary to the
conventional formula based on the CNT. Furthermore, the estimated energy
barrier for the crystallization is surprisingly small compared to that for the
equilibrium dynamics. By comparing the crystallization and aging dynamics
quantitatively, we show that a coupling between aging and crystallization is
the key for understanding the rapid crystallization of deeply supercooled
liquids or glasses.
