Ergodic approximation in the theory of binary molecular solutions

An exact representation of the classical partition function of a two-component solution with interatomic potentials of a general form via a functional integral is obtained. The ergodic Weyl theorem (ergodic approximation) is used to calculate the functional integral. It is obtained an expression for the Helmholtz free energy via Fourier transforms of interatomic potentials, including renormalization in the case of their singularity. It is shown that, in order to correctly describe the separation of binary solutions into phases, it is nesessary to take into account the ergodic contribution to the Helmholtz free energy. The necessary condition of the phase separation in binary solutions is established.