Relativistic corrections to the atomic volumes of the actinide metals

Abstract

The effect of spin-orbit coupling upon the energy band structure of the light actinide metals has been examined. A measure of the importance of spin-orbit coupling is the ratio of the number of f electrons in the j=⁵/₂ and j=⁷/₂ bands, which approaches 6/8 when spin-orbit coupling is small. The computed ratio from ab initio self-consistent relativistic calculations for the metals Ac-Am varies from 0.75 for Ac to 2.4 for Am. The change in atomic volume due to the preferential occupation of the j=⁵/₂ band has also been computed. It is small for the elements Ac-U but the volumes of Np-Am increase progressively. There is a corresponding decrease in the change of volume for the expected phase transition in americium under pressure.