SPATIAL STRUCTURE IN LIQUID WATER UNDER NORMAL AND CRITICAL CONDITIONS

Liquid state structure has traditionally been characterized with the radial distribution functions between atoms. While these functions are routinely available from X-ray diffraction and neutron scattering experiments or from computer simulations, they can not be interpreted unambiguously to provide the spatial order in a molecular liquid. A direct approach to determining the spatial structure in the liquid state is demonstrated here and it focuses upon spatial distribution functions of oxygen atoms in liquid water and amorphous ice in various state points. These functions are calculated in molecular dynamics simulations. They reveal an important role played by "interstitial" non tetrahedral coordination in phase transitions of water.