Effect of short- and long-range forces on the structure of water: temperature and density dependence

Abstract

The individual effects of short-range and long-range forces on the structure of water, a prerequisite for developing a perturbation theory, are assessed using a decomposition of realistic water—water potential models into trial potentials. Computer simulations for one typical liquid density and a number of temperatures ranging from the freezing temperature up to supercritical ones, and for several densities on a supercritical isotherm were performed. The trial potentials were constructed from the ST2 and TIP4P potentials and it is shown that for both potentials the results are practically identical. It is shown that (i) regardless of the thermo-dynamic conditions and potential models used, the structure of water and the mutual orientational arrangement of water molecules, given by a set of site—site correlation functions, are determined nearly exclusively only by the short range forces, and (ii) for high density states the effect of the short range electrostatic part of the intermolecular potential on the spatial arrangement of the water molecules rapidly decreases with increasing temperature but does not become negligible.