Are light alkali metals still metals under high pressure?

TL;DR

This paper investigates the behavior of light alkali metals under high pressure, proposing that an ionic insulating phase may explain why hydrogen does not metallize easily and predicting a metal-insulator transition in sodium around 100 GPa.

Contribution

It introduces a mean-field model of the extended Hubbard Hamiltonian on a bcc lattice to predict ionic phases and metal-insulator transitions in alkali metals under high pressure.

Findings

Ionic insulating phase predicted for hydrogenoid bcc solids between r_s 1.0 and 2.6

Failure to achieve hydrogen metallization explained by ionic phase formation

Sodium expected to undergo a metal-insulator transition near 100 GPa

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.