EQUATION-OF-MOTION TREATMENT OF THE IMPURITY ANDERSON MODEL WITH A FINITE ON-SITE COULOMB REPULSION

The impurity Anderson model with a finite Coulomb repulsion U has been studied by using the Conventional equation-of-motion treatment for the f-electron Green's function. To get a closed equation, two types of approximations are incorporated. One is to neglect, in a large U limit, higher order Green's functions which involve three f-electron annihilation operators. The other is to linearize the equation of motion by using a projection operator method. The average valency n(f) and the spectral density of states (DOS) of f electrons are evaluated from the self-consistent equation for the Green's function. Results for n(f) are in good agreement with the exact results of the Bethe ansatz method, and the obtained spectral DOS exhibits a well-known three-peak structure. Effects of finite U and finite temperature on the spectral DOS are discussed.