Multipole decomposition of LDA plus U energy and its application to actinide compounds

A general reformulation of the exchange energy of 5f shell is applied in the analysis of the magnetic structure of various actinides compounds in the framework of LDA + U method. The calculations are performed in a convenient scheme with essentially only one free parameter, the screening length. The results are analyzed in terms of different polarization channels due to different multipoles. Generally it is found that the spin-orbital polarization is dominating. This can be viewed as a strong enhancement of the spin-orbit coupling in these systems. This leads to a drastic decrease in spin polarization in accordance with experiments. The calculations are able to correctly differentiate magnetic and nonmagnetic Pu system. Finally, in all magnetic systems an unusual multipolar order is observed, whose polarization energy is often larger in magnitude than the one of spin polarization.