BULK PROPERTIES OF THE LIGHT ACTINIDES FROM FIRST PRINCIPLES

摘要

The unusual ground state properties of the light actinide metals have served a continuous challenge for the theory since the pioneering work by Skriver et al. [1]. In this self-consistent, scalar relativistic calculation it was shown that the atomic number dependence of the equilibrium atomic volumes and other bulk properties supports the picture of itinerant 5f electrons for the lighter elements of the series (plutonium or lighter), and a Mott localization takes place between Pu and Am [2] (the atomic volume of americium is about 50 per cent larger than those of the earlier elements). However, the theory was not able to explain why Pu has a somewhat larger atomic volume than that of Np, although in both cases the f electrons are assumed to be of itinerant nature. The main difficulty arises from the fact that these elements, especially plutonium, have rather complex zero temperature crystal structures; the α - Pu structure is monoclinic with 16 atoms per unit cell. In addition, the relativistic effects are very important for these heavy elements, and the 6s, 6p semicore states contribute to the bonding essentially and should be considered as band states (which, in the case of a linear method, doubles the number of diagonalizations to be performed in total energy calculations).