A COMPARISON OF DIFFERENT APPROXIMATE TWO-COMPONENT RELATIVISTIC THEORIES OF MANY-ELECTRON SYSTEMS: A CASE STUDY OF THE IONIZATION ENERGIES OF TWO-ELECTRON IONS |

M. Barysz^{a}, N. Flocke^{b} and J. Karwowski^{c}^{a}Instytut Chemii, Uniwersytet Mikołaja Kopernika, Gagarina 7, 87-100 Toruń, Poland^{b}Department of Chemistry and Physics, University of Florida Gainesville, Florida 32611, USA^{c}Instytut Fizyki, Uniwersytet Mikołaja Kopernika, Grudziądzka 5/7, 87-100 Toruń, Poland |

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Received: January 18, 2001; in final form May 9, 2001 |

The corrections to the ionization energies of two-electron ions due to relativistic effects are studied by different two-component relativistic methods. In particular, the results obtained by the standard Pauli-Cowan-Griffin method and by two variants of the Douglas-Kroll-Hess method (the one based on the free-particle transformation and the one in which the transformation accounts for the nuclear potential) are compared with those calculated using the four-component Dirac-Fock method. Limits of applicability of each of these methods have been indicated. Results acceptable in the whole range of the nuclear charge (relativistic corrections accurate up to 4% for Z<=85) are given only by the Douglas-Kroll-Hess method which goes beyond the free-particle transformation. Each of the other two approaches either underestimates or overestimates the corrections due to relativistic effects. |

DOI: 10.12693/APhysPolA.99.631 PACS numbers: 31.15.-p, 31.30.Jv |