Ground State of a Magnetic Impurity in a Metal

A new type of ground-state wave function for a magnetic impurity in a metal is postulated, and its parameters are determined variationally. The basic idea is that formation of a singlet ground state requires the phase shifts of all electrons near the Fermi surface to be adjusted simultaneously. The method resembles a configuration-interaction treatment of in-out correlation. The result is a phase shift which varies as (E-E_F)¹² near the Fermi surface and a binding energy larger than in previous variational treatments.