Molecular dynamics investigation of the crystal–fluid interface. VI. Excess surface free energies of crystal–liquid systems

We present the first direct calculation by simulation of the excess surface free energy of a crystal–liquid interface. We perform these calculations on the (111), (100), and (110) interfaces of a truncated Lennard-Jones face-centered-cubic crystal–liquid system at the triple point by the molecular dynamics technique. Bulk crystal and liquid systems are first cleaved and then combined with one another reversibly. The work required to do this is integrated and equals the excess surface Helmholtz (and Gibbs) free energy. The free energies are found to be 0.35±0.02, 0.34±0.02, and 0.36±0.02 (dimensionless units) for the (111), (100), and (110) faces, respectively. The three faces are therefore energetically isotropic within our error bars and the equilibrium form of the crystal is approximately spherical.