Connecting Diffraction Experiments and Network Analysis Tools for the Study of Hydrogen-Bonded Networks

A self-consistent scheme is presented that is applicable for revealing details of the microscopic structure of hydrogen-bonded liquids, including the description of the hydrogen-bonded network. The scheme starts with diffraction measurements, followed by molecular dynamics simulations. Computational results are compared with the experimentally accessible information on the structure, which is most frequently the total scattering structure factor. In the case of an at least semiquantitative agreement between experiment and simulation, sets of particle coordinates from the latter may be exploited for revealing nonmeasurable structural details. Calculations of some properties concerning the hydrogen-bonded network are also described, in the order of increasing complexity: starting with the definition of a hydrogen bond, first and second neighborhoods are described via spatial correlations functions. Attention is then turned to cyclic and noncyclic hydrogen-bonded clusters, before cluster size distributions and percolation are discussed. We would like to point out that, as a result of applying the novel protocol, these latter, rather abstract, quantities become consistent with diffraction data: it may thus be argued that the approach reviewed here is the first one that establishes a direct link between measurements and elements of network theories. Applications for liquid water, simple alcohols, and alcohol-water liquid mixtures demonstrate the usefulness of the aforementioned characteristics. The procedure can readily be applied to more complicated hydrogen-bonded networks, like mixtures of polyols (diols, triols, sugars, etc.) and water, and complex aqueous solutions of even larger molecules (even of proteins).