Dense Low-Coordination Phases of Lithium

Ab initio density-functional-theory calculations and a structure-searching technique are used to identify candidate high-pressure phases of lithium (Li). We predict threefold coordinated structures to be stable in the pressure range 40–450 GPa and fourfold structures at higher pressures. We describe these low-coordination phases as elemental electrides. All of the stable phases are metallic but the Cmca-24 structure, and two distortions of it which are marginally the most stable in the pressure range 86–106 GPa, are nearly semiconducting with densities of electronic states at the Fermi energy of only a few percent of the free-electron value.