  In this Letter we report a simulation study in which we compare the
solid-liquid interfacial free energy of NaCl at coexistence, with the value
that follows from the height of the homogeneous nucleation barrier. We find
that the two estimates differ by more than 100%. Similar, although smaller
discrepancies are found for crystals of hard-sphere colloids and of
Lennard-Jones ("argon") particles. We consider a variety of possible causes for
this discrepancy and are forced to conclude that it is due to a finite-size
effect that cannot be corrected for by any simple thermodynamic procedure.
Importantly, we find that the surface free energies that follow from real
nucleation experiments should be subject to large finite size effects. Taking
this in to account, we obtain quantitative agreement between the simulation
data and the surface free energy of NaCl that follows from nucleation
experiments. Our finding suggests that most published solid-liquid surface free
energies derived from nucleation experiments will have to be revised.

Materials Science