Structures and optical properties of solid hydrogen at ultrahigh pressures

Abstract

The electronic energy bands in structures whose primitive cell contains up to four molecules are studied with full optimization of the structures on the basis of GGA and LDA band calculations. Above 250 GPa, the eventual optimal structure obtained by the GGA or the LDA calculation is Cmca, which is a layered structure with the molecular bonds lying in planes and which has a metallic band structure with no band gaps. The metallic property of the band structure remains unchanged even if the molecular bonds in the plane of the Cmca are inclined so that the atoms in the molecule lie out of the plane. The electronic bands of the Cmca structure and those of some other candidate structures are discussed in the light of recent experimental results. Effects of the occupation of electronic states on the predicted optimal structures are also studied.