Precision calculation of the low-lying excited states of the Rf atom

Precision calculations of the ground and low-lying excited electronic states of the Rf atom (Z = 104) were performed. The relativistic effects were taken into account with the Dirac-Coulomb-Breit Hamiltonian. The finite nucleus size was taken into account in the Fermi model (A = 267). The correlation effects were described by the combined scheme that we suggested previously, which proved to be efficient: The relativistic coupled clusters method with one- and two-particle cluster amplitudes in the Fock space was used for describing the correlations of 44 outer electrons of the Rf atoms in a fairly large atomic basis set, and for the four valence electrons occupying the 7s, 7p, and 6d states, the contributions from three- and four-particle cluster amplitudes were taken into account using the complete configuration interaction method, but in a relatively small basis set. The relativistic configuration and term for the ground state of the Rf atom were refined, and the energies of its excitation to low-lying states were calculated. The accuracy of the calculation by the generalized relativistic effective core potential method was evaluated by comparing the results with those obtained similarly using the Dirac-Coulomb-Breit Hamiltonian.