Morphologies of organic crystals: Sensitivity of attachment energy predictions to the model intermolecular potential

The influence of the intermolecular potential on predicted growth morphologies is investigated. We compare the morphologies calculated with the attachment energy model for epsilon-caprolactam (C2/c), beta-succinic acid (P2(1)/c), hexamethylene tetramine (I (4) over bar 3m), pentaerythritol (I (4) over bar), and urea (P (4) over bar2(1)m). Five different model potentials that have been developed for modeling organic crystal structures are used. These show a progressive improvement in the accuracy of the electrostatic model and a variety of empirical parametrizations of the repulsion-dispersion terms. Although the lattice energies and absolute attachment energies vary quite significantly, there are only minor variations in the predicted morphologies. The assumptions in the attachment energy model generally contribute more to any discrepancy between the predicted and observed morphologies than the variations between different model potentials that could be considered appropriate for modeling. However, the attachment energy model readily provides a reasonable estimate of the dominant faces of the vapor-grown habit, suitable for most chemical engineering purposes.