Dynamical response of intermediate-valence and Kondo systems

Dynamical properties of valence-fluctuating systems are discussed by the use of a self-consistent perturbation theory from the atomic limit. Results for the dynamical magnetic susceptibility x (ω) and the 4f-electron density of states ρ{variant}_4f(ε{lunate}) are reported for a model Ce impurity system. Comparison is made with available exact results for ρ{variant}_4f(0), x(0) and Im x;(ω)/ω (ω → 0) at zero temperature. The present theory provides accurate dynamical information over a wide excitation-frequency range at arbitrary temperature.