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).