Theoretical Evidence for a Dense Fluid Precursor to Crystallization

We present classical density functional theory calculations of the free-energy landscape for fluids below their triple point as a function of density and crystallinity. We find that, both for a model globular protein and for a simple atomic fluid modeled with a Lennard-Jones interaction, it is free-energetically easier to crystallize by passing through a metastable dense fluid in accord with the Ostwald rule of stages but in contrast to the alternative of ordering and densifying at once as assumed in the classical picture of crystallization.

Figure 1

The phase diagram for a LJ potential (left) and the ten Wolde-Frenkel potential (right). The solid and dashed lines are from the model and the points are from simulation, Refs. 1, 23, 24, respectively. The dotted lines connect the coexistence points used in Figs. 2, 3.

Figure 2

The Gibbs free-energy barriers, per atom, for the tWF potential. The solid curve is for the classical path and the broken curve results from densification followed by ordering.

Figure 3

Same as Fig. 2 for the LJ potential.