Brillouin-Wigner-like quasidegenerate perturbation theory for intermediate effective operators is discussed. Due to the self-consistent approach to the calculation of projectors onto perturbed model states, an a priori partitioning of the model space into a main model space and an intermediate space is avoided. Small energy denominators do not appear in any order. As for the intermediate states, the accuracy of results and the norm of effective interactions can be controlled; one can achieve an almost exact description of the lowest intermediate states and gradual increase of errors when going up in energy. Numerical examples are presented and discussed.

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