Statistical thermodynamics of multicomponent systems of nonspherical molecules taking account of the short-range order in a quasichemical approximation

It is shown that short-range order can be taken into account effectively for a liquid multicomponent system (mixture) of molecules with internal (particularly orientation) degrees of freedom within the framework of a quasichemical approximation (in the Guggenheim formulation) by using a vector in the space of internal states of the molecule (correlation vector) which is introduced together with the ordinary set (vector) of occupation numbers describing the longrange order. A closed system of equations is obtained in the correlation vector representation for the thermodynamic functions and occupation numbers of chemically distinct components in the space of internal states of the molecule, and its variational formulation is given. The possibilities for using the results obtained in the theory of the liquid-crystal state are discussed. © 1978 Plenum Publishing Corporation.