A comparative study of finite nucleus models far low-lying states of few-electron high-Z atoms

We studied low-lying states of lithium-like and beryllium-like ions with Z = 80 and 100 less than or equal to Z less than or equal to 120 for differential effects due to variation of the nuclear charge density distribution. The latter was represented by exponential, Gauss-type, and Fermi-type models, standardized to a common rms radius. Numerical Hartree-Fock and Dirac-Fock-Coulomb calculations were performed. Changes in total energies due to the use of different models become increasingly important for high Z in relativistic approaches. Different models may even lead to different sequences of atomic states, and thus energy differences between those states may vary by an order of magnitude. (C) 2000 Elsevier Science B.V. All rights reserved.