THEORETICAL INVESTIGATION OF THE HIGH-PRESSURE CRYSTAL-STRUCTURES OF CE AND TH

The high-pressure crystal structures of Ce and Th are studied theoreti cally by means of a full potential linear muffin-tin orbital technique , where the generalized gradient correction to density-functional theo ry has been implemented. A crystallographic phase transition from fcc to bet is found for alpha-Ce at about 10 GPa, in good agreement with e xperiment The calculated pressure dependence of the crystallographic c ia ratio (of the bet structure) is in good agreement with experiment. For alpha-Ce a subsequent transition to the hcp crystal structure is p redicted at about 1600 GPa. For Th a continuous transformation from fe e to bet at 45 GPa is found, confirming recent experimental findings. Also for this material the calculated pressure dependence of the cryst allographic c/a ratio (of the bet structure) is in good agreement with experiment. For Th we also predict a transformation to the hcp crysta l structure at even higher pressures.