The multiplet electronic structure of U ion: relativistic all-electron ab initio approach

Relativistic all-electron ab initio calculations were performed in the case of the free U ion. The spin-orbit-free low-lying states were calculated using the State-Averaged Restricted Active Space Self-Consistent Field (SA-RASSCF) method with the inclusion of spin-orbit effects. The Atomic Mean-Field Integral (AMFI) technique was used to compute the spin-orbit states. The lowlying spin-orbit energy levels which are originating from 5f 6d configuration have deviations of about 0.04 - 0.40 eV from that reported in the NIST data, whereas the higher excited states have large deviations. The assignment of some low-lying excited states which are not given in the favour of experimental results in the NIST data are discussed in the present work.