Energy and Specific Heat Due to an Impurity Atom in a Dilute Alloy

Abstract

The ground-state energy for the Anderson model of an impurity atom in a paramagnetic host metal is evaluated as a function of the impressed magnetic moment. Within the Hartree-Fock approximation we find that the ground-state energy has an absolute minimum for a finite value of the magnetic moment, corresponding to a stable localized magnetic moment. When correlations are included within the low-density approximation, the energy has its minimum for vanishing magnetic moment and the system cannot magnetize, in agreement with the results of Schrieffer and Mattis. The expression for the ground-state energy is extended to nonzero temperature and the specific heat due to the dilute impurities is calculated. It is shown that the anomalous specific heat derived by Anderson within the Hartree-Fock approximation is spurious.