Theoretical studies of the actinides: method calibration for the UO22+ and PuO22+ ions

As part of method assessment for the theoretical study of actinide systems, we have performed 1-component relativistic pseudopotential calculations for the uranyl and plutonyl ions. The calculated spectroscopic constants compare well with fully relativistic 4-component results at both the Hartree–Fock and correlated levels of theory. We deduce that second-order spin–orbit effects in these systems are minor and show that the 1-component method chosen (B3LYP in particular) gives reliable results at low computational cost. The ground state of the plutonyl ion has been determined as 3Hg.