Refined Ionic Models for Lanthanide and Actinide Halides

摘要

We present an ionic model of binding which is aimed at quantitatively allowing for formation of bound molecular units in simulation studies of ionic liquids, with main emphasis on RX_3 compounds (where R is a metal of the rare-earth series from La to Lu and X = F, Cl, Br or I) by an analysis of data on the static and dynamic structure of their molecular monomers. The model owes its usefulness to the self-consistent inclusion of the electric dipoles induced by the combined action of internal electric fields and of closed-shell overlaps. With a similar approach the model has been used in the determination of the ionic interactions in AX_4 compounds (where A is an atom in the actinide series from U to Am). The main focus on the model calculations for the above systems has been on the effective valence, the ionic radius and the electric polarizability of metal ions. In R-halides and A-halides we briefly review the results that we have obtained for the structure and the vibrational frequencies of the molecular monomers as well as for the Dy_2Cl_6, Dy_2Br_6, La_2F_6 and Ce_2F_6 molecular dimers. A comparison between our results and available data are also presented.