BAND-GAP CLOSURE OF AR(H-2)(2) UNDER PRESSURE

We present a theoretical study of the behavior of the energy gap of Ar (H-2)(2) under pressure, considering several possible orientational st ructures for the H-2 molecules. The calculations are performed within a tight-binding formalism parametrized for solid molecular H-2. Effect s of orientational disorder of the hydrogen molecules are also conside red. We find that the orientation of the H-2 molecules has a very stro ng effect on the band gap of Ar(H-2)(2), except at low pressures. Our calculations indicate that metallization of Ar(H-2)(2) by band-gap clo sure occurs when the distance between nearest-neghbor H-2 molecules in the experimentally determined hexagonal structure is 1.57 Angstrom. T he required pressure is estimated to be above 400 GPa.