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 interfa ces. The free energy functional we use has a square-gradient form, wit h the parameters for a Lennard-Jones interaction potential determined by a modified weighted density approximation (MWDA) applied locally th rough the liquid-solid interface. We explore the role of the density c hange on freezing in crystal and melt growth, and discover a significa nt asymmetry between freezing and melting both close to and far from t he equilibrium freezing point. The behavior of the superheated solid i s governed by the close proximity of a spinodal, whereas in the underc ooled liquid there is no evidence for a spinodal and the growth at lar ge undercoolings is affected instead by the density deficit that appea rs in front of the growing interface. Comparisons are made with other density functional approaches and with computer simulations. (C) 1996 American Institute of Physics.