Prediction of Crystal Habit

As discussed in the previous section, crystal habit is a function of both the internal structure of the crystal and the external conditions of growth. A fundamental problem that has been of interest for many years is how to employ this information to predict the habit of crystals grown under realistic conditions. 

The equilibrium shape of a crystal is that of its minimum energy. This is called the Wulff condition and indicates that the area of faces present will be such as to minimize the Gibbs free energy of the crystal. Unfortunately, the observed habit of crystals grown from solutions is often quite different from the prediction by the Wulff condition. 

F-faces (flat), each of which is parallel to at least two PBC vectors. 

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The work discussed in the previous paragraphs provides the framework for the prediction of crystal habit from internal structure. The challenge is to add realistic methods for the calculation of solvent and impurities effects on the attachment energies (hence the crystal habits) to allow this method to provide prediction of crystal habit. Initial attempts of including solvent effects have been recently described (71. 721. The combination of prediction of crystal habit from attachment energies (including solvent and impurity effects) and the development of tailor made additives (based on structural properties) hold promise that practical routine control and prediction of crystal habit in realistic industrial situations could eventually become a reality. 

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