A simulated X-ray diffraction study of liquid water: Beyond the spherical-atom approximation

The total electron density of a water molecule differs significantly from the superposition of the O + H + H spherical-atom densities by way of bonding and lone-pair electron charge accumulations. Such non-spherical electron density features on neighbouring molecules typically lie in the range 2-4 Angstrom apart in liquid water. Their influence on the diffracted coherent X-ray intensity for liquid water has been simulated, based on molecular dynamics data and non-spherical atomic electron deformation functions, for the water molecule. It is found that in the liquid water sample, the deformation densities on different molecules interfere significantly in the scattering process, but the effect is largely eliminated because of statistical cancellations over Q vector directions and time, The result is that the influence from the deformation densities on g(r) is large for intramolecular distances, but small for intermolecular distances.