Reliable modeling of the electronic spectra of realistic uranium complexes

We present an EOMCCSD (equation of motion coupled cluster with singles and doubles) study of excited states of the small [UO2](2+) and [UO2](+) model systems as well as the larger U(VI)O2(saldien) complex. In addition, the triples contribution within the EOMCCSDT and CR-EOMCCSD(T) (completely renormalized EOMCCSD with non-iterative triples) approaches for the [UO2](2+) and [UO2](+) systems as well as the active-space variant of the CR-EOMCCSD(T) method-CR-EOMCCSd(t)-for the U(VI)O2(saldien) molecule are investigated. The coupled cluster data were employed as benchmark to choose the "best" appropriate exchange-correlation functional for subsequent time-dependent density functional (TD-DFT) studies on the transition energies for closed-shell species. Furthermore, the influence of the saldien ligands on the electronic structure and excitation energies of the [UO2](+) molecule is discussed. The electronic excitations as well as their oscillator dipole strengths modeled with TD-DFT approach using the CAM-B3LYP exchange-correlation functional for the [U(V)O2(saldien)](-) with explicit inclusion of two dimethyl sulfoxide molecules are in good agreement with the experimental data of Takao et al. [Inorg. Chem. 49, 2349 (2010)].