ZERO-POINT MOTION AND THE INSULATOR-METAL TRANSITION IN SOLID MOLECULAR-HYDROGEN

Candidate structures for molecular hydrogen in the 150 GPa pressure ra nge are examined using ab initio frozen-phonon calculations in the loc al density approximation. Vibronic zero-point motion yields important contributions to the relative energies of metallic versus insulating p hases. A first-order insulator-metal transition is found, with feature s in qualitative accord with experiment. Our results imply that an obs erved transition in solid molecular hydrogen is an insulator-metal-mol ecular-orientation transition driven by the vibron zero-point motion i tself.