Liquid-gas critical point in the method of collective variables

Partition function of $N$ atoms interacting via long-range and short-range potentials is presented in the form of functional integrals. It is shown that the problem can be formulated by means of some adequate lattice. Coefficients of the expression obtained are functions of the wave vectors of this lattice and can be reduced to the functions dependent only on the average density of the particles. As a result, a possibility appears to calculate the partition function of liquid-gas system by the methods developed previously for the Ising model.