Crystal Structure and Interaction Dependence of the Crystal-Melt Interfacial Free Energy

We examine via molecular simulation the dependence of the crystal-melt interfacial free energy $\gamma$ on molecular interaction and crystal structure (fcc vs bcc) for systems interacting with inverse-power repulsive potentials, $u(r)=ϵ(\sigma /r{)}^n$, $6\le n\le 100$. Both the magnitude and anisotropy of $\gamma$ are found to increase as the range of the potential increases. Also we find that ${\gamma }_{\mathrm{b}\mathrm{c}\mathrm{c}}<{\gamma }_{\mathrm{f}\mathrm{c}\mathrm{c}}$, consistent with recent observations that some fcc forming fluids nucleate via formation of metastable bcc nuclei. The anisotropy in $\gamma$ is also seen to be smaller in the bcc systems. By extrapolation, we also obtain an improved estimate of $\gamma$ for hard spheres.

Figure 1

(a) The scaled crystal-melt interfacial free energies ${\gamma }_1={\gamma }^{*}/T^{*1+2/n}$ for the inverse-power series as functions of $1/n$. The open and filled symbols show the data for systems with bcc and fcc crystal structures, respectively. The points at $1/n=0$ represent extrapolations of the finite $n$ data, as discussed in the text. (b) The same as (a) except for the crystal-melt interfacial free energy per interfacial particle ${\overline{\gamma }}_1={\gamma }_1{\Gamma }_c^{-2/3}$.