Density functional theory of crystal growth: Lennard-Jones fluids

We employ an extension of density functional theory to the dynamics of phase transitions in order to study the velocities of crystal growth and melting at planar undercooled and superheated crystal-melt interfaces. The free energy functional we use has a square-gradient form, with the parameters for a Lennard-Jones interaction potential determined by a modified weighted density approximation (MWDA) applied locally through the liquid-solid interface. We explore the role of the density change on freezing in crystal and melt growth, and discover a significant asymmetry between freezing and melting both close to and far from the equilibrium freezing point. The behavior of the superheated solid is governed by the close proximity of a spinodal, whereas in the undercooled liquid there is no evidence for a spinodal and the growth at large undercoolings is affected instead by the density deficit that appears in front of the growing interface. Comparisons are made with other density functional approaches and with computer simulations. (C) 1996 American Institute of Physics.