Density functional theory for the freezing of soft-core fluids

We present a simple density functional theory for the solid phases of systems of particles interacting via soft-core potentials. In particular, we apply the theory to particles interacting via repulsive point Yukawa and Gaussian pair potentials. We find qualitative agreement with the established phase diagrams for these systems. The theory is able to account for the bcc-fcc solid transitions of both systems and the re-entrant melting that the Gaussian system exhibits.

Figure 1

Phase diagram of the GCM. The solid line is the bcc melting boundary and the dashed line is the fcc melting boundary, both determined using the Lindemann criterion—see the text. The dot-dashed line is the locus of points where the Helmholtz free energies of the bcc and fcc phases are equal. The dotted lines are the phase boundaries obtained from the computer simulations of Prestipino et al. [19].

Figure 2

Same as Fig. 1, except that now the solid line is the locus of points where the Helmholtz free energies of the bcc and liquid phases are equal. The liquid state free energy is calculated using the rather crude approximation in Eq. (13).

Figure 3

Phase diagram of the YCM. The solid line is the bcc melting boundary and the dashed line is the fcc melting boundary, both determined using the Lindemann criterion—see the text. The dot-dashed line is the locus of points where the Helmholtz free energies of the bcc and fcc phases are equal.

Figure 4

Same as Fig. 3, except here the results are plotted in terms of the variables $\kappa$ and $\Gamma$. The symbols joined by solid lines are the simulation results of Hamaguchi et al. [34].