Ensembles are further grouped into molecules. In this context, a molecule refers to a species or system with a unique chemical identity, independent of its precise geometry or properties. Thus, each molecule can be characterized by its InChI key, which is automatically computed. While this definition is not restrictive (e.g. when modelling transition states and reaction products within the same "molecule" object), it nevertheless serves as a useful organizational tool. In this way, large numbers of calculations are classified based on their chemical relevance.