QUASI-CHEMICAL THEORIES OF ASSOCIATED LIQUIDS

It is shown how traditional development of theories of fluids based up on the concept of physical clustering can be adapted to an alternative local clustering definition. The alternative clustering definition ca n preserve a detailed valence description of the interactions between a solution species and its near-neighbours, i.e., cooperativity and sa turation of coordination for strong association. These clusters remain finite even for condensed phases. The simplest theory to which these developments lead is analogous to quasi-chemical theories of cooperati ve phenomena. The present quasi-chemical theories require additional c onsideration of packing issues because they do not impose lattice disc retizations on the continuous problem. These quasi-chemical theories d o not require pair decomposable interaction potential energy models. S ince calculations may be required only for moderately sized clusters, it is suggested that these quasi-chemical theories could be implemente d with computational tools of current molecular electronic structure t heory. In this way an intermediate step of approximate force field gen eration can be avoided.