This chemical filter can be framed equivalently in terms of electron counting or valency, which is common in the study of semiconductors . The filter applies to a broad range of inorganic materials, particularly those classified as being formed of ionic and covalent interatomic interactions, where the charge neutrality principle holds. However, it may not be suitable for describing metallic alloys (e.g. Cu1-xZnx), intermetallic compounds (e.g. Ni3Al), and nonstoichiometric compounds (e.g. YBa2Cu3O7-δ), as these materials often involve different chemical bonding and variable compositions that go beyond the scope of simple charge neutrality considerations. Special consideration would also be required for mixed-valence compounds where a single element appears in the same compound with multiple oxidation states. For example, the binary compound magnetite Fe3O4 contains an equal number of Fe(II) and Fe(III) ions, and thus would be described as a ternary compound by SMACT based on its three constituent species.