Role of Strong Correlations in Disproportionation of Aqueous Actinides

We study the role of strong electronic correlations in the disproportionation of aqueous actinide complexes An(aq) and AnO$_2$(aq) where An = U, Np, and Pu. Correlations are expected to be important due to the localized nature of the actinide 5f orbitals. We first confirm that relativisitic DFT\footnote{ADF2004.01, \urllink{SCM}{http://www.scm.com}, Theoretical Chemistry, Vrije Universiteit.}, despite yielding reasonable geometries and bond lengths, fails to reproduce\footnote{P. J. Hay, R. L. Martin, and G. Schreckenbach, J. Phys. Chem. A {\bf 104}, 6259 (2000).} experimentally observed degeneracies of the redox potentials\footnote{D. L. Clark in {\it Los Alamos Science} No. 26 Vol. II (2000).}. By using a continuum model for the water beyond the first solvation sphere we are able to construct and diagonalize reduced Hubbard-like models of the actinide complexes, and incorporate the missing physics of strong intra-atomic Coulomb repulsion\footnote{M. X. LaBute {\it et al.}, J. Chem. Phys. {\bf 116}, 3681 (2002).} \footnote{D. V. Efremov {\it et al.}, \urllink{cond-mat/0303414}{http://arxiv.org/abs/cond-mat/?0303414}; E. Runge {\it et al.}, \urllink{cond-mat/0402124}{http://arxiv.org/abs/cond-mat/?0402124}.}.