Ground-state structures of atomic metallic hydrogen

Ab-initio random structure searching using density functional theory is used to determine the ground-state structures of atomic metallic hydrogen from 500-GPa to 5-TPa. Including proton zero-point motion within the harmonic approximation, we estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near 500-GPa (r_s=1.23) that remains stable to 1-TPa (r_s=1.11). At higher pressures, hydrogen stabilizes in an... ABCABC... planar structure that is similar to the ground state of lithium, but with a different stacking sequence. With increasing pressure, this structure compresses to the face-centered cubic lattice near 3.5-TPa (r_s=0.92).