Multiconfiguration Dirac–Hartree–Fock Adjusted Energy-Consistent Pseudopotential forUranium: Spin–Orbit Configuration Interaction and Fock-Space Coupled-Cluster Study ofU4+ and U5+

摘要

In order to assess the accuracy of a recently adjusted relativistic energy-consistent small-core pseudopotentialfor uranium, the U5+ (5f1 subconfiguration) spin-orbit splitting as well as the fine structure of the U4+(5f2subconfiguration) spectrum have been calculated. The pseudopotential has been adjusted to four-componentall-electron data, i.e., at the multiconfiguration Dirac-Hartree-Fock level using the Dirac-CoulombHamiltonian with a Fermi nucleus charge distribution and perturbatively including the Breit interaction. Itsperformance in a dressed effective Hamiltonian spin-orbit configuration interaction framework is comparedto that of an older scalar-relativistic Wood-Boring adjusted pseudopotential, supplemented by a valencespin-orbit term, as well as to all-electron calculations using the Douglas-Kroll-Hess Hamiltonian. Electroncorrelation is accounted for by the multireference configuration interaction method with and without theDavidson correction and with different frozen-orbital spaces. Our best calculations show satisfactory agreementwith experimental data; i.e., the mean absolute (relative) deviations amount to 183 (2.4%) and 948 cm-1(5.1%) for the U5+ and the U4+ fine-structure energy levels, respectively. Even better agreement, comparableto the one for rigorous highly correlated four-component all-electron data, is obtained in intermediateHamiltonian Fock-space coupled-cluster calculations applying the new pseudopotential.