Low-frequency magnetic response in valence fluctuating and heavy fermion systems

By starting from an Anderson impurity Hamiltonian, a simple approximation for the spectral densities of the occupied and the empty f state is suggested. With it such thermodynamic quantities like the partial f occupancies go over, in the zero temperature limit, into the results of variational calculations. The approximation is applied in the presence of a crystalline electric field in order to calculate χ″(w,T). A comparison with previous, more elaborate calculations is provided for the case of vanishing CEF splittings.