A numerical study on the validity of the Breit-Pauli approximation

Abstract
The numerical importance of relativistic higher order corrections to the total energies of atoms in the Breit-Pauli approximation is studied. The corrections are small until Z approximately=20, but grow very fast for larger values of Z. The significance of the relativistic first-order correction of the Hartree-Fock wavefunction on the Breit and Pauli energies is demonstrated; it is of order alpha 2Z4. Double 1/Z- alpha 2Z2 expansions of Dirac-Fock energies are determined numerically. The correlation-relativity cross term is mainly due to the Breit correction in the standard theoretical framework; it increases the nonrelativistic 1s2 correlation energy by about 0.014Z2% and becomes the dominant contribution for Z)150.

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