Subcritical and supercritical water radial distribution function

A theoretical and analytic expression For the first shell. and an analytic empirical expression for the whole radial distribution function (RDF) of wa ter are introduced. All the asymptotic limits and functionalities of the RD F with temperature and density are incorporated in these expressions. An ef fective Kihara pair potential function is presented for water intermolecula r interactions which incorporates the hydrogen bonding by using the chain a ssociation theory. The intermolecular pair potential parameters are adjuste d to the experimental x-ray diffraction data of water RDF at various temper atures. The predicted first-shell results for water near critical and in su percritical conditions compare satisfactorily with the available neutron di ffraction RDF data, with the simulation RDF results, and with the empirical RDF curves. The empirical expression initially proposed for the RDF of the Lennard-Jones fluid is extended to predict the RDF and the isothermal comp ressibility of water to conditions where experimental or simulated data are not available. Comparison with the Lennard-Jones fluid shows that the heig ht of the first peak of water RDF changes much less at subcritical and supe rcritical conditions compared to that of the Lennard-Jones fluid which decr eases appreciably going from subcritical to supercritical conditions.