Abstract :
Neutron diffraction data for water and ice in the form of OO, OH and HH partial structure factors now exist over a temperature range 220–673 K, and at pressures up to ∼400 MPa. In order for these data to be useful for comparing with different computer simulations and theories of water, it is first necessary to Fourier transform them to the corresponding site–site radial distribution functions. The process of doing this is not straightforward because of the inherent systematic uncertainties in the data, which arise primarily in the case of neutron scattering, from the inelasticity or recoil effects that can distort the experimental data. In this paper, it is shown that the empirical potential structure refinement procedure, which attempts to fit a three-dimensional ensemble of water molecules to all three partial structure factors simultaneously, leads to improved reliability in the extracted radial distribution functions. There are still some uncertainties, primarily associated with the hardness of the repulsive core of the intermolecular potential, which current data are not precise enough to resolve. The derived empirical potentials show some variability associated with particular experiments. General trends can be discerned however which indicate polarisation effects may be significant when effective intermolecular potentials are used over a wide temperature and density range.
