The step energy
as a habit controlling factor: Application to the morphology prediction
of aspartame, venlafaxine, and a yellow isoxazolone dye
Deij, M. A., Meekes, H., Vlieg, E.
CRYSTAL GROWTH & DESIGN 7 (10): 1949-1957 OCT 2007
Abstract: In this paper, we
report on the use of step energies in crystal morphology prediction as
an improvement and computationally fast alternative to the Bravais,
Friedel, Donnay, and Harker (BFDH) and attachment energy methods. One
of the major improvements is a morphology prediction that is dependent
on the driving force for crystallization. Step energies are calculated
using STEPLIFT, an automated procedure to find the lowest step energies
of infinitely long and straight steps. These steps are constructed by a
combination of the connected nets of two nonparallel flat faces
(F-faces), one representing the step terraces, the other the step edge.
Step energies obtained in all relevant directions on a specific crystal
face are used for a two-dimensional (2D) Wulff construction. This leads
to the equilibrium shape of a 2D nucleus having the lowest energy,
which can be used as a classification for the nucleation barrier, for
example, in 2D birth and spread growth. Using the 2D nucleus energy, a
link between the atomistic description of the steps and the macroscopic
growth morphology is made using crystal growth theory to calculate
growth rates as a function of the driving force for crystallization.
This procedure is applied successfully to predict the crystal
morphology of aspartame II-A, venlafaxine, and two polymorphs of a
yellow isoxazolone dye.