This effect is very useful for cold cathodes and for flat panel displays , for example. Work done with Brian Davidson. It is an ionic crystal in which a molecule loses an electron and thereby becomes the cation , and the electron locates itself in an interstitial position and by itself, that is, without an atom or a molecule, become the anion. It seems clear, from the joint implication of our theoretical work and the experimental data, that in this molecular crystal the valence electron of the Cs atom sits in the open interstice and thereby stabilizes the crystal. The plot shows an isosurface of the density of the 'electride state' in the interstitial region of the crystal.
Blue atoms are oxygen, red atoms are carbon, orange atoms are hydrogen.
Our results also suggest that this system is a Mott insulator, and might form an excellent realization of a system described by the simple single band Hubbard model without orbital degeneracy lurking to cause complications. Work done with David Singh, Henry Krakauer, and Cree Haas.