Electronic spectrum of UO22+ and [UO2Cl4]2- calculated with time-dependent density functional theory

The electronic spectra of UO22+ and [UO2Cl4](2-) are calculated with a recently proposed relativistic time-dependent density functional theory method based on the two-component zeroth-order regular approximation for the inclusion of spin-orbit coupling and a noncollinear exchange-correlation functional. All excitations out of the bonding sigma(+)(u) orbital into the nonbonding delta(u) or phi(u) orbitals for UO22+ and the corresponding excitations for [UO2Cl4](2-) are considered. Scalar relativistic vertical excitation energies are compared to values from previous calculations with the CASPT2 method. Two-component adiabatic excitation energies, U-O equilibrium distances, and symmetric stretching frequencies are compared to CASPT2 and combined configuration-interaction and spin-orbit coupling results, as well as to experimental data. The composition of the excited states in terms of the spin-orbit free states is analyzed. The results point to a significant effect of the chlorine ligands on the electronic spectrum, thereby confirming the CASPT2 results: The excitation energies are shifted and a different luminescent state is found. (C) 2007 American Institute of Physics.