OPTICAL AND MAGNETOOPTICAL SPECTROSCOPY OF URANIUM AND PLUTONIUM COMPOUNDS - RECENT THEORETICAL PROGRESS

First-principles calculations are reported which illustrate that, for those actinide compounds where the 5f electrons are sufficiently deloc alized, energy band theory based upon the local,spin-density approxima tion (LSDA) describes the optical and MO spectra reasonably well. Exam ples which we examine in detail are URhAl and UFe2. The delocalized LS DA approach meets limitations for those actinide compounds, where the electrons in the correlated 5f shell are nearly localized. Just as in the case of lanthanide compounds having localized 4f electrons, a sati sfactory description of the optical spectra could be obtained by using a generalization of the LSDA, in which explicitly f electron Coulomb correlations are taken into account (LSDA+U approach). A third group c onsists of compounds in which the 5f electrons are neither fully deloc alized nor localized, but have experimentally been classified as quasi localized. The suitable theoretical approach to such compounds is yet to be resolved. We further consider the Pu monochalcogenides, the unus ual physical properties of which were previously treated with differen t models, and discuss the optical spectrum of PuTe. (C) 1998 Elsevier Science S.A.