2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/28388The flow equation method has been used to calculate the energy of single impurity in a superconductor for the Anderson model with $U \neq 0$. We showed that the energy of the impurity depends only of the $Δ^{2}_{R}$ (renormalized order parameter) which depends on the renormalized Hubbard repulsion$U^R$. For a strong Hubbard repulsion $U^R = U$ and $Δ^R = Δ^I$ the effect of the $s-d$ interactions are nonrelevant, a result which is expected for this model.Latex fileCondensed Mattertext