On the constitution of sodium at higher densities

Using density functional theory the atomic and electronic structures of sodium are predicted to depart substantially from those expected of simple metals for r(s) < 2.48 (p > 130 GPa). Newly predicted phases include those with low structural symmetry and semimetallic electronic properties (including zero-gap semiconducting limiting behavior), and even those that raise the possibility of superconductivity, all at currently achievable pressures. Important differences emerge between sodium and lithium at high densities, and these are attributable to corresponding differences in their respective cores.