Solid-Fluid Coexistence for Inverse-Power Potentials

We report Monte Carlo studies of solid-fluid coexistence for the soft-sphere potential: φ(r)=ε(σr)ⁿ. Applying a recently developed integration method that proceeds along a coexistence line, we determined coexistence for essentially a continuum of softness s≡1/n from $s=0$ (hard spheres) to ca. $s=0.25$. For $s<0.16$, we estimate that fcc is the stable crystal, and that bcc is stable for softer potentials; however, this result is not conclusive. We find substantial disagreement with early coexistence data for n=12, 9, 6, and 4, while confirming more recent studies for n=12 and 6.