Schrieffer-Wolff transformation
= Schrieffer-Wolff transformation
{c}
A perturbative <unitary conjugation> eliminating couplings between chosen separated energy sectors. For $H=H_0+V$ and an <anti-Hermitian> $S$ satisfying $[S,H_0]=-V$ at leading order, the transformed <Hamiltonian> contains $\tfrac12[S,V]$ at second order. Exactly resonant coupled states must be retained in a common block. The method was used for the Anderson-to-Kondo relation by <John Robert Schrieffer> and <P. A. Wolff>.