Relativistic many-body perturbation theory using analytic basis functions

The authors show that the compact representation of the complete Dirac spectrum provided by finite analytic basis set methods allows the study of relativistic electron correlation effects. The instantaneous Coulomb and low-frequency Breit interactions are treated using a unified formalism. The principles of this computational method are illustrated by calculations of the electronic structure of the argon ground state. The calculations reveal that the terms in the perturbation expansion corresponding to the self-consistent modification of the one-electron orbitals due to the Breit interaction result in the most significant relativistic many-body effect.