Anderson orthogonality theorem

The Anderson orthogonality theorem is a theorem in physics by the physicist P. W. Anderson.

It relates to the introduction of a magnetic impurity in a metal. When a magnetic impurity is introduced into a metal, the conduction electrons will tend to screen the potential $$V(r)$$ that the impurity creates. The N-electron ground state for the system when $$V(r) = 0$$, which corresponds to the absence of the impurity and $$V(r) \neq 0$$, which corresponds to the introduction of the impurity are orthogonal in the thermodynamic limit $$N \to \infty $$.