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 pressure induced phase transitions: Ce, fcc-->bct-->hcp; The fcc-->bct-->hcp; Pa, bct-->alpha-U-->bct-->hcp; U, alpha-U-->bct-->bcc; Np, alpha-Np-->beta-Np-->bcc; Pu, alpha-Pu-->alpha-Np -->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.