LIQUID-GAS CRITICAL-POINT

Integration of the grand partition function in the vicinity of of liquid-gas critical point is performed. Essential peculiarities of the problem are the following: consideration of the problem in the expanded phase space, consisting of sub-space of the Cartesian coordinates and sub-space of the collective variables (CV) of the density fluctuations modes (the first sub-space describes interactions at short distances, the second one is appropriate for long distances); provement that curves for the cumulants defining the Jakhobian of transition to the CV have horizontas plates in the vicinity of zero values of wave vectors. It enables one to reduce the liquid-gas critical point problem to the Ising model at constant external field an certain crystal lattice. Chemical potential isotherm as well as density gap are determined below the critical