*4.2. Prediction of Catechol Crystal Morphology in Vacuum*

Figure 3a depicts the crystal morphology of catechol in vacuum predicted by the AE model. The prismatic crystal had six dominant faces, owing to not only crystallography geometry but also intermolecular interactions. Figure 3b visualizes the interactions between the catechol molecules calculated and generated by the Crystal Graph in the morphology module, with the blue and red lines representing strong and weak interactions, respectively. Previous studies indicated that crystals grow faster along the direction with strong molecular interactions [44]. Therefore, catechol crystals grow faster along the blue line direction and the surfaces with fast growth rate may disappear, leaving the slowly growing surface appear in the final morphology with six important faces, (1 0 −1), (1 0 1), (0 1 1), (1 1 0), (0 0 2) and (1 1 −1). In the AE model, the surface with higher absolute value of *E*att has stronger ability to adsorb catechol molecules, which means a relatively faster growing rate of the crystal face, and vice versa. As listed in Table 2, the most important face is (1 0 −1) occupying more than 48% of the total habit facet area, followed by (1 1 −1) and (1 0 1) with 20% and 19% in total areas, respectively. Therefore, (1 1 0), (0 0 2) and (0 1 1) faces grow faster with relatively larger |*E*att| among all the crystal faces, which are of lower morphological importance and are more likely to disappear.

**Figure 3.** The predicted catechol crystal morphology in the vacuum (**a**) and the intermolecular interactions in the catechol unit cell calculated by the Crystal Graph (**b**).

**Table 2.** The parameters of the catechol crystal faces in the vacuum predicted via the attachment energy (AE) model.

