Calculation of the free energy of a system of two-particle clusters

Hubbard operators are used to find a convenient form for the Hamiltonian of a system of interacting two-particle clusters. The partition function of the system is represented in the form of a functional integral with respect to field variables, The coefficients that determine the non-Gaussian distribution of the phases of the density fluctuation of the spin moment in the free energy functional are calculated. An expression for the free energy of the system is obtained in the Gaussian approximation.