A derivation is given of the Feynman rules to be used in the perturbative computation of the Green's functions of a generic quantum many-body theory when the action which is being perturbed is not necessarily quadratic. Some applications are discussed.

We recently developed a scheme to use low-cost calculations find single twist angle where the coupled cluster doubles energy of calculation matches twist-averaged in finite unit cell. used initiator full configuration interaction quantum Monte Carlo as an example exact method beyond theory show that this selected approach had comparable accuracy methods cluster. Furthermore, at least for small ...

All-order extensions of relativistic atomic many-body perturbation theory are described and applied to predict properties of heavy atoms. Limitations of relativistic many-body perturbation theory are first discussed and the need for all-order calculations is established. An account is then given of relativistic all-order calculations based on a linearized version of the coupled-cluster expansio...