  The behavior of saturated aqueous sodium chloride solutions under a constant
external electric field (E) was studied by molecular dynamics (MD) simulation.
Our dynamic MD simulations have indicated that the irreversible nucleation
process towards crystallization is accelerated by a moderate E, but retarded or
even prohibited under a stronger E, which can be understood by the competition
between self-diffusion and drift motion. The former increases with E resulting
in the acceleration of the nucleation process, and the latter tears oppositely
charged ions more apart under a stronger E leading to the deceleration of
nucleation. Moreover, our steady-state MD simulations have indicated that a
first-order phase transition happens in saturated solutions only when the
applied E is below a certain threshold Ec, and the ratio of crystallized ions
does not change with the electric field. The magnitude of Ec increases with
concentration, because larger clusters are easy to form in a more concentrated
solution and require a stronger E to dissociate them.
