Crystallization of fcc (111) and (100) crystal-melt interfaces: A comparison by molecular dynamics for the Lennard-Jones system

Abstract

The crystal growth rates of Lennard-Jones fcc (face-centered cubic) (111) and (100) faces into the melt have been studied as a function of undercooling by molecular dynamics. The (100) grows without activation energy barrier at rates determined by the difference in the free energies of the crystal and melt phases, and the arrival rate of atoms across a plane determined from the kinetic theory of gases. The maximum velocity occurs at approximately half the melting point and represents 80 m/s for argon. The (111), on the other hand, grows at rates two to three times lower than this; the exact rate being size dependent. The growth kinetics are now activated and resemble Wilson–Frenkel behavior. However, the step responsible for such activation is not the simple liquid diffusion of Wilson–Frenkel theory, but rather the concerted motion of atoms at the interface selecting either all fcc or all hcp (hexagonal close packed) triangular lattice sites before a layer can grow.