THEORETICAL DETERMINATION THAT ELECTRONS ACT AS ANIONS IN THE ELECTRIDE CS-CROWN-5)2.E-((15)

ELECTRIDES are crystalline salts formed from complexed alkali-metal ca tions. There has been some dispute as to whether the valence electron from the alkali ion becomes a trapped interstitial anion1,2 or resides at or near the alkali-metal nucleus3. If the former description holds , electrides would represent stoichiometric counterparts of ionic insu lators containing 'F-centre' electronic defects. Experiments1,2 have s o far failed to resolve the question. Here we present ab initio self-c onsistent density-functional calculations4 of the electron distributio n in the electride Cs+(15-crown-5)2.e-. We find that a spatially local ized electron is located at the anion site, in accord with the F-centr e model. Although the potential is in fact repulsive in this region, t he electron is apparently forced to reside here by the need to lower i ts kinetic energy. We suggest that this picture may hold for other ele ctrides as well.