Structure of water: Short-ranged versus long-ranged forces

By transforming a realistic water-water potential separately into long-ranged and short-ranged systems and using computer simulations it is shown that the structure of water is determined primarily by short-ranged (both repulsive and attractive) forces. An extended primitive model of water is then shown to provide both the spatial and orientational arrangement of water molecules in the liquid phase in semi-quantitative agreement with diffraction experiments. Practical importance of this finding is exemplified by formulating a perturbation expansion about the primitive model reference and its individual steps are analyzed with respect to their implementation.