Relativistic calculations of the ground state energies and the critical distances for one-electron homonuclear quasi-molecules

The ground-state energies of one-electron homonuclear quasi-molecules for the nuclear charge number in the range Z=1-100 at the chemical distances R= 2/Z (in a.u.) are calculated. The calculations are performed for both point- and extended-charge nucleus cases using the Dirac-Fock-Sturm approach with the basis functions constructed from the one-center Dirac-Sturm orbitals. The critical distances R_cr, at which the ground-state level reaches the edge of the negative-energy Dirac continuum, are calculated for homonuclear quasi-molecules in the range: Z=85-100. It is found that in case of U_2^{183+} the critical distance R_cr = 38.42 fm for the point-charge nuclei and R_cr = 34.72 fm for extended nuclei.

Model operator approach to the Lamb shift calculations in relativistic many-electron atoms

A model operator approach to calculations of the QED corrections to energy levels in relativistic many-electron atomic systems is developed. The model Lamb shift operator is represented by a sum of local and nonlocal potentials which are defined using the results of ab initio calculations of the diagonal and nondiagonal matrix elements of the one-loop QED operator with H-like wave functions. The model operator can be easily included in any calculations based on the Dirac-Coulomb-Breit Hamiltonian. Efficiency of the method is demonstrated by comparison of the model QED operator results for the Lamb shifts in many-electron atoms and ions with exact QED calculations.

Transition frequency shifts with fine structure constant variation for Fe II: Breit and core-valence correlation correction

Transition frequencies of Fe II ion are known to be very sensitive to variation of the fine structure constant alpha. The resonance absorption lines of Fe II from objects at cosmological distances are used in a search for the possible variation of alpha in cause of cosmic time. In this paper we calculated the dependence of the transition frequencies on alpha^2 (q-factors) for Fe II ion. We found corrections to these coefficients from valence-valence and core-valence correlations and from the Breit interaction. Both the core-valence correlation and Breit corrections to the q-factors appeared to be larger than had been anticipated previously. Nevertheless our calculation confirms that the Fe II absorption lines seen in quasar spectra have large q-factors of both signs and thus the ion Fe II alone can be used in the search for the alpha-variation at different cosmological epochs.