Investigation of the Two-Particle-Self-Consistent Theory for the   Single-Impurity Anderson Model and an Extension to the Case of Strong   Correlation
  The two-particle-self-consistent theory is applied to the single-impurity Anderson model. It is found that it cannot reproduce the small energy scale in the strong correlation limit. A modified scheme to overcome this difficulty is proposed by introducing an appropriate vertex correction explicitly. Using the same vertex correction, the self-energy is investigated, and it is found that under certain assumptions it reproduces the result of the modified perturbation theory which interpolates the weak and the strong correlation limits. 
Tetsuro Saso