In this example, given that the C atom is sp 2 hybridized, the two H-C-C angles should be about 120°. This process is performed for all atoms in the BEANTR molecule and the completed molecule is obtained after step 4c. Step (5) reconstructs the complete super-cell with appended H atoms. Step (6) reduces the super-cell back to the original unit cell with all the coordinates for the missing H atoms now known. Finally, sanity checks are performed to verify that the structure is correct. The structure is checked against the expected chemical formula (if provided in the CIF file from the CSD). In addition, RDKit is used to repeat step 4b and confirm that the explicit valence matches with the type of hybridization for each atom. If the sanity check fails, the user may have to attach H atoms manually. HAppend is not limited to PAHs and may be used to add missing H atoms to other types of organic molecules.