Total-energy calculations are reported for compressed solid Ar which suggest that the observed 1-atm fcc phase should transform to an hcp structure prior to metallization, and it in turn should transform to a bcc structure at pressures above metallization. It is argued that this structural sequence follows from the effects of hybridization between the l valence band and the l+1 conduction band as the gap narrows and closes, and that all rare-gas solids are likely to undergo an hcp→bcc transition with metallization occurring near, if not within, the range of hcp stability. The lower-pressure fcc→hcp transition in insulating Ar should occur below 230 GPa.

• Received 24 December 1985

DOI:https://doi.org/10.1103/PhysRevB.33.5344