Moreover, it is likely that a topological analysis of the electron density for numerous alkali and alkali metal systems (including crystals at ambient pressures, or gas phase molecules) would be able to satisfy the first two topological features of an electride, and detect an ELF basin, though its contour value would be notably lower than 1. Some concrete examples are ambient pressure lithium or sodium, prototypical examples of nearly free electron metals. Therefore, it is important to define criteria that discriminate metals that have these characteristics from electrides. One possibility is imposing a value of near 1 for the ELF, another would be to define an upper bound for the Laplacian, however currently insufficient studies have been performed to provide a meaningful guideline. Furthermore, it is unclear whether a crystalline electride should also possess a band-gap, like the molecular organic crown ether and cryptand complexes, or at least a pseudo-gap, or other features to distinguish it from a pure metal. In this context, one way to discriminate electrides could be to consider only values of the ELF close to 1 at the position of the excess electron. To date, the lack of an unambiguous, and generally agreed upon ELF minimum, has created some confusion in the characterization of inorganic electrides. Also, the value of the Laplacian seems to be relevant, but this feature is generally less studied. 85