Diagram technique for $s$–$d$ model

Temperature diagram technique with unperturbed Hamiltonian including the strong intracell interaction of $d$-electrons is proposed, $s$–$d$ hybridization operator is taken into account as the perturbation. Wick's theorem for the averages of the products of creation and destruction “time” operators belonging to the same lattice point is absent practically due to the choice of the unperturbed Hamiltonian. Diagram technique is introduced on the basis of using the Wick theorem for $s$-electron operators and the scheme method for the $d$-electron operators. This technique is used to analyse and remove the temperature divergences of one-point diagram contributions, which arise due to the degeneration of the unperturbed level of the system at $(1/kT)\equiv\beta\to\infty$.