  Water and silicon are chemically dissimilar substances with common physical
properties. Their liquids display a temperature of maximum density, increased
diffusivity on compression, they form tetrahedral crystals and tetrahedral
amorphous phases. The common feature to water, silicon and carbon is the
formation of tetrahedrally coordinated units. We exploit these similarities to
develop a coarse-grained model of water (mW) that is essentially an atom with
tetrahedrality intermediate between carbon and silicon. mW mimics the
hydrogen-bonded structure of water through the introduction of a nonbond
angular dependent term that encourages tetrahedral configurations. The model
departs from the prevailing paradigm in water modeling: the use of long-ranged
forces (electrostatics) to produce short-ranged (hydrogen-bonded) structure. mW
has only short-range interactions yet it reproduces the energetics, density and
structure of liquid water, its anomalies and phase transitions with comparable
or better accuracy than the most popular atomistic models of water, at less
than 1% of the computational cost. We conclude that it is not the nature of the
interactions but the connectivity of the molecules that determines the
structural and thermodynamic behavior of water. The speedup in computing time
provided by mW makes it particularly useful for the study of slow processes in
deeply supercooled water, the mechanism of ice nucleation, wetting-drying
transitions, and as a realistic water model for coarse-grained simulations of
biomolecules and complex materials.
