Ligands are predefined as well. They can be either chosen from around 160 common built-in ligands or customed by users. The selected ligands are aligned to the coordination sites sequentially following the order of ligand denticity to minimize the global steric repulsion. Simple and fast force field optimizations are recommended after the entire structure is built for the sake of downstream tasks. To design functional complexes, ChemSpaX 85 targets exploring the local chemical space of molecular scaffolds. It allows users to place functional groups on a given complex to generate a series of derivatives from an initial skeleton. Similar to molSimplify, the functional substituents are specified from a predefined ligand database which includes 80 common ligands. And it also supports post-functionalization for either the newly placed substituent or the entire functionalized structure. Another feature of ChemSpaX is that it allows iterative functionalization on a skeleton, i.e., the output of one functionalization can be the input for the next functionalization. As a result, ChemSpaX can build large molecules with more than 200 atoms.