**5. Conclusions**

In this study, we successfully simulated the crystal habits of catechol in isopropanol, methyl acetate and ethyl acetate using the MAE model which takes solvent effects into consideration. The analysis on the calculated attachment energy indicates that the interactions on solvent−crystal interfaces had essential effects on catechol crystal morphology in all three experimental systems. Factors such as surface structure and diversity of interaction types were explored to find their synergy for crystal shapes.

The (1 0 −1) face was the most morphologically dominant crystal face because its relatively flat surface provided less adsorption sites for both solvent and solute molecules, leading to a relatively slow face growth. The molecular alignment, roughness and diffusion coefficient analysis on dominant crystal faces indicates that the (0 0 2) and (0 1 1) faces disappeared in final crystal morphology due to the competitive adsorption of molecules favorable for solutes to continuously adsorb on the surface. The RDF curves reveal that several types of interactions contributed to real crystal morphology in solvent systems, of which the hydrogen bond was a crucial factor to analyze the change in the aspect

ratios of crystal. The shape distinctions of catechol crystals were mainly attributed to the attachment energy as well as the diverse strength of hydrogen bonds between solvent molecules and catechol molecules on (1 0 1) and (1 1 −1) faces. Moreover, the simulated crystal morphology of catechol was consistent with the crystallized ones obtained from all three solvents, proving the practicability of the MAE model to select optimal crystal morphology in industrial crystallization using simulation methods.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4352/10/4/316/s1, Table S1: The cleaved depth and size of catechol crystal faces to form a simulation supercell. Figure S1: The simulated XRD pattern of catechol crystal. Figure S2: The RDF analysis between catechol and methyl acetate on the (1 1 0) face.

**Author Contributions:** Conceptualization, L.Z. (Ling Zhou) and D.Z.; methodology, D.Z., S.Z. and C.W.; software, S.Z., D.Z. and P.C.; validation, S.Z. and Q.Y.; formal analysis, D.Z., P.C. and C.W.; investigation, D.Z., P.C. and J.D.; data curation, D.Z., S.Z. and L.Z. (Ling Zhou); writing—original draft preparation, D.Z. and S.Z.; writing—review and editing, D.Z., S.Z., J.D., C.W., Y.H. and Q.Y.; visualization, D.Z. and P.C.; supervision, B.H. and L.Z. (Lina Zhou); project administration, Q.Y. and H.H.; funding acquisition, Q.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors are grateful for the financial support of the National Natural Science Foundation of China (No. 21706183).

**Conflicts of Interest:** The authors declare no conflict of interest.
