Li T.C., Gunnarsson O., Schonhammer K., Zwicknagl G.
The authors discuss the calculation of Fermi liquid parameters for the Anderson impurity model. An earlier calculation of de Chatel (1982) is extended to a finite f-f-Coulomb interaction U and corrections of order 1/Nf are studied, where Nf is the degeneracy of the localised level in the Anderson model. The lack of momentum conservation in the impurity model is found to be a complication, since the low-lying excited states are not automatically orthogonal in approximate calculations. In low-order 1/Nf calculations the impurity induced quasi-particle density of states is found to have a singularity at the Fermi energy. The origin of this singularity is traced. The complications in obtaining thermodynamic properties via the calculation of Fermi liquid parameters is contrasted to the accuracy obtained in a 'direct approach', in which the calculations are performed to orders (1/Nf)0, (1/Nf)1 and (1/Nf)2.
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