Are light alkali metals still metals under high pressure?

Abstract

The extended Hubbard Hamiltonian on a bcc lattice is studied at half-filling and for a finite hopping between next-nearest-neighbours, in mean-field approximation. An ionic insulating broken-symmetry phase is predicted for any hydrogenoid bcc solid in the density range 1.0 < r sub s < 2.6. The occurrence of an ionic phase would explain the failure to achieve hydrogen metallization at high pressures. Moreover, a metal-insulator transition is expected for sodium in the 100 GPa region.