  We show evidence from computer simulations of a universal feature in the
atoms dynamics of simple liquids that heralds the freezing transition. We
develop a physically transparent model to shed light on the physics responsible
for the precursory effect. We find that the freezing point is concomitant with
the crossover of two characteristic time scales, namely the average period of
oscillation of the liquid configuration in a minimum of the potential energy
surface, and the average time separating transits between potential energy
minima as a result of the continuous dynamical rearrangement of particles. When
entering the undercooled regime, the transit time becomes smaller than the
period of oscillation, and the delicate balance between the disordering effects
of thermal agitation and the ordering effects of interactions can be
destabilized in favor of the periodic order. Finally, we demonstrate that the
discovered precursory feature gives rise to a new efficient method for
determining the liquid-solid coexistence line of real materials from atomistic
simulations, which, unlike other methods commonly used in materials science,
does not require knowing the crystalline structure of the solid phase.
