EXTENDED 5-SITE PRIMITIVE MODELS OF WATER - THEORY AND COMPUTER-SIMULATIONS

Theoretical results for the thermodynamic properties of the extended f ive-site primitive model of water, based on the thermodynamic perturba tion theory of Wertheim, are presented and compared with simulation da ta. The theory performs well for both the internal energy and the pres sure for models with a short range of hydrogen bonding but its accurac y rapidly deteriorates as this range reaches large realistic values. I t is shown that the crucial point of the theory is the description of the structure of the fluid of so-called pseudohard bodies which plays the role of a reference system. The available theoretical description of the structure of such a fluid deteriorates with increasing non-sphe ricity and, consequently, the same holds for the perturbation theory.