Abstract:
A temperature diagram technique is developed for calculating the Green's function of the
operators of changing atomic configurations. Because Wick's theorem does not hold for
the mean values of these operators, an expansion in semi-invariants is used Instead of
the standard diagram technique. The formaIism is used to find the Green's function of the
admixture $d$-electron in the Anderson model. It is shown that in the case when one of the
admixture levels is near the Fermi surface summation of the Ieading diagrams in the
logarithmic approximation is equivalent to decoupling of the two-time Green's functions
and reduces to a renormalization of the admixture level.
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