Band structures and cohesive properties of high pressure phases of solid iodine

Abstract

The band structures of high pressure phases of iodine are calculated on the basis of the local-density-functional formalism and a norm-conserving pseudopotential. The density of states (DOS) of the body-centered-tetragonal phase (BCT phase) at 49GPa is compared with that of a hypothetical face- centered-cubic phase (FCC phase) with the same atomic volume. It is found that the Fermi-level of the BCT phase is located off a peak of the DOS but that of the FCC phase is on a plateau, which originates from a saddle point singularity due to degenerate p-bands. This is in agreement with the experiment that the BCT structure is a stable phase at this atomic volume over the FCC structure. We argue from the band structures the reason why the FCC structure becomes a stable phase over the BCT structure at high pressures. We have calculated also the total energy of the FCC phase as a function of the atomic volume. The lattice constant at 64GPa is reproduced within 1% by the calculation.