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Abstract
The development of standard MBPT for single-reference and multi-reference cases is reviewed, and its extension to the relativistic case in the form of the Dirac–Coulomb–Breit (DCB) approximation is described. The latter scheme is non-covariant, and the recent development of a fully covariant MBPT scheme is discussed. This is based upon a new scheme for quantum-electrodynamical (QED) calculations, the covariant-evolution-operator method, which is combined with standard MBPT. This scheme is fully compatible with the relativistically covariant Bethe–Salpeter equation. Some numerical results of the new scheme are given.
Acknowledgements
The author wants to thank his co-workers Sten Salomonson and Daniel Hedendahl for fruitful collaboration. This work has been supported by the Swedish Research Council (VR).
Notes
Notes
1. We use here natural or relativistic units: c = ħ = m e = ε0 = 1, e 2 = 4πα, α being the fine-structure constant.
2. In the following we shall leave out the subscript ‘I’.