Theory of the crystal structures of cerium and the light actinides

First-principles theory, based on the density-functional approach, is used to study the crystal structures of Ce and the light actinides (Th-Pu) at low temperatures as a function of hydrostatic pressure. Calculated ground-state properties, such as crystal structure, atomic volume and bulk modulus, are shown to be very well described within this theory. We present the following pressureinduced phase transitions: Ce, fcc -> bct -> hcp; Th, fcc -> bct -> hcp; Pa, bct -> alphaU bct -> hcp; U, alpha-U -> bct -> bcc; Np, alpha-Np -> beta-Np -> bcc; Pu, alpha-Pu -> alphaNp -> beta-Np -> bcc. We explain the occurrence of low-symmetry (complex) structures in these metals as a consequence of a symmetry-breaking mechanism that shows similarities to a Peierls distortion. The ultimate high-pressure phases are well accounted for in a canonical model for the f bands for these metals.