On the range of water structure models compatible with X-ray and neutron diffraction data.

Area of Science:

• Physical Chemistry
• Materials Science
• Biophysics

Background:

• Understanding the structure of liquid water is crucial for many scientific disciplines.
• Diffraction data provides insights into molecular arrangements but requires sophisticated analysis.

Purpose of the Study:

• To evaluate the structural information content of diffraction data for bulk water.
• To determine the extent to which X-ray and neutron diffraction data constrain water models.
• To explore the variability of water structure models consistent with experimental data.

Main Methods:

• Utilized the reverse Monte Carlo (RMC) method to fit diffraction data.
• Performed simultaneous and separate fits to X-ray and neutron diffraction data.
• Incorporated various hydrogen-bonding constraints to generate structural models.

Main Results:

• Neutron data alone adequately describes O-H and H-H pair-correlation functions (PCFs), but not O-O PCFs.
• Four distinct structural models of liquid water were generated, all fitting the diffraction data equally well.
• Tetrahedrality in the hydrogen-bond network is not strictly defined by the data, even for three-body correlations.
• Molecular dynamics models (TIP4P-pol2 and SPC/E) showed discrepancies with experimental neutron data.
• RMC fits yielded optimal PCFs but revealed significant variability in the intermolecular O-H peak.

Conclusions:

• Diffraction data provides essential constraints on possible water structures.
• Additional experimental data is necessary to reduce the ambiguity and narrow down the range of valid water structure models.
• The precise structure of liquid water remains an active area of research requiring complementary data sources.