The sire.convert submodule includes functionality to interconvert the molecular information in MoleculeData with the corresponding molecule or system objects in the libraries RDKit 14 , OpenMM 15 , Gemmi and BioSimSpace 8 . This can be used directly, e.g. creating RDKit molecules via the RDKit SMILES functions, then converting to BioSimSpace for forcefield parameterisation, then converting to OpenMM for GPU-accelerated molecular dynamics simulation (figure ). Or, alternatively, it is used in the background by higher-level sire functions that leverage the capabilities of those packages, e.g. using sire.load to load a PDBx/mmCIF file will call Gemmi to load the file into a gemmi::Structure, and will then convert that into a sire.system.System comprising one MoleculeData per molecule.