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CI schemes are conceptually simple, invariant to orbital rotations, but
suffer from the lack of size consistence. The modification of the diagonal
(a dressing) permits to include higher-order diagrams, leading to
size-consistent CI schemes and even CCSD, still relatively expensive.
The diagonal approximation of the dressed CI comes back to second-order
perturbation theory, including however selfconsistent couplings between
excited determinants.
We will examine the advantages and drawbacks of this dressed perturbation theory with respect to orbital localization and periodic structures. |
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