14-12E

The calculation method of the grand partition function of a simple fluid model in frames of generalized lattice model, where each cell may contain random number of particles, was proposed. As an interaction potential between particles the Morse potential was chosen. In course of calculations summation over number of particles and integration over it's coordinates were performed. Using a simplest approximation the state equation valid in wide temperature ranges was obtained. At temperatures lower than critical one, the presence of horizontal plots at curve of the pressure dependence on the density was established.