Layering transitions and the structure of dense hydrogen

¹ Laboratory of Atomic and Solid State Physics, Cornell University Ithaca, NY 14853-2501, USA
² Theoretical Division, Los Alamos National Laboratory - Los Alamos, NM 87545, USA

Received: 5 February 1996
Accepted: 15 April 1996

Abstract

Recent theories of the structure of solid hydrogen at high pressure have tended to focus on the hexagonal close-packed (hcp) class of structures typical of low pressure, the contribution of the zero-point motion often being neglected. Here we examine the energy of solid hydrogen at high pressure in different structures, using density-functional theory augmented by the self-consistent harmonic approximation. Above a relative compression we report an orthorhombic structure, Cmca, that has lower energy (both static and zero-point) than the lowest-energy hcp structures, indicative of a possible layering or martensitic transition occurring in the vicinity of the recently observed high infrared activity.