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

The individual effects of short-range and long-range forces on the structur e of water, a prerequisite for developing a perturbation theory, are assess ed using a decomposition of realistic water-water potential models into tri al potentials. Computer simulations for one typical liquid density and a nu mber of temperatures ranging from the freezing temperature up to supercriti cal ones, and for several densities on a supercritical isotherm were perfor med. The trial potentials were constructed from the ST2 and TIP4P potential s and it is shown that for both potentials the results are practically iden tical. It is shown that (i) regardless of the thermodynamic 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 fun ctions, are determined nearly exclusively only by the short range forces, a nd (ii) for high density states the effect of the short range electrostatic part of the intermolecular potential on the spatial arrangement of the wat er molecules rapidly decreases with increasing temperature but does not bec ome negligible.