Electrides are a unique class of ionic materials in which the anions are stoichiometrically replaced by localised electrons. This unique chemical structure confers a number of desirable properties. However, the majority of the electride crystals are temperature unstable making experimental examination of these materials difficult. Theoretical methods are not hindered by the practical problems afflicting the experimental approaches and, as such, present an ideal alternate route for the ongoing investigation of electrides.

Density-functional theory (DFT) is used to conduct this theoretical investigation. We first explore the potential systematic errors associated with common density functionals when modelling a localised electron within a crystal void, which is the central characteristic of the electride crystals. Bare DFT is shown to excessively delocalise the interstitial electron, while use of continuum solvent models with DFT overly localises this electron. In the latter case, we find the excessive localisation phenomena is dependent only on the applied solvent correction and any electronicstructure method that uses a similar correction will exhibit the same errors.

The alkali metal-ligand complexes, the building blocks of the electride crystals, are modelled and thermodynamic cycles constructed, highlighting the energy changes that occur when these complexes form. The ionisation potential of the alkali metal-ligand complexes is found to be consistently between 1 and 2 eV, regardless of the alkali metal or ligand molecule used. We propose this be used as a design criteria for future computational testing of potential electride-forming alkali metal-ligand complexes.

DFT analysis of all of the known electride crystals (at the time) is conducted. As well as establishing a common ground from which to theoretically discuss the electrides (the first such study to do so), we identify the 'electride state' for all of the organic electride crystals. This state is associated with the localised electron and resides between the conduction and valence band in the band structure. By modifying the initial self-consistent field guess, we were able to find the first all-electron solutions for the magnetic states of the organic electrides. These magnetic states reproduced the expected anti-ferromagnetic behaviour, in some cases to a remarkable degree of accuracy.

Finally, we computationally apply pressure to the simplest organic electride, Cs+(15-crown-5)2e-. We find that the magnetic properties of the electride change significantly upon compression, eventually becoming ferromagnetic. This switch from an anti-ferromagnetic to ferromagnetic ground state, termed piezomagnetism, means that Cs+(15-crown-5)2e-, and potentially other electrides, can develop a spontaneous magnetic moment under pressure. Piezomagnetism is a rare property that has just as many potential applications as the well known piezoelectric materials. The range of pressure computationally applied is easily accessible to modern experimental techniques and this result should be reasonably easy to verify experimentally.

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