There are numerous 4-element chemical spaces for which there are missing 3-element chemical spaces. For example, the chemical space C = {Mg, Mn, F, O} is missing C' = {Mg, F, O}, which means that we cannot determine if a structure within C can be decomposed into structures within C'. Hence, any present calculation of E h will not be reliable until all the missing subset chemical spaces are determined. There are currently 264 hypothetical structures in the database within C, which are deposited in the database along with their computed E h . Some of these materials have very low E h values such as MgMn 5 O 7 F (mp-2226474) with E h ~ 60 meV, which means that it is a metastable phase which might be synthesisable. It will only be a matter of time until this value changes.