1ST PRINCIPLES STUDIES OF CRYSTAL-STRUCTURES OF F-ELEMENTS

The crystal structures of some selected f band metals (Ce, Th, Pa, U and Am) have been calculated from first principles. It is demonstrated that the onset of low symmetry structures correlates with the increasing f occupation of the valence states. It is also shown that pressure is an important parameter for these types of studies, and that the occupation of the various orbitals of the valence band depends on it. One can thus modify (increase) the f occupation of a certain system, simply by applying a pressure. Since the crystal structure depends on the f occupation, for these systems, one can drive different crystal structures as function of pressure. We present one such example, the FCC --> BCT phase transition at approximately 1 Mbar for Th.