Schematic illustration of two different classes of water species with different hydrogen bond distortions from the ice tetrahedral structure. Left: the distortions of the hydrogen bonds are relatively small and the tetrahedral symmetry can be approximated as maintained, denoted double donor (DD); the two hydrogen atoms are both involved in donating hydrogen bonds. Right: the distortions are asymmetrical where one donor hydrogen bond is intact and the other is highly distorted, denoted single donor (SD).
Resulting fits to diffraction data from simultaneous RMC fits to XD and ND data as well as E-field distribution using the DD model (left) and asymmetrical model (right). The diffraction data sets are (a) XD as derived from the data of Ref. 23 and [(b)–(f)] ND from Ref. 15 with (b) , (c) and , (d) and , (e) and , and (f) .
Partial O–O (top), O–H (middle), and H–H (bottom) PCFs for the DD (left) and SD (right) models.
Histograms characterizing structural parameters for the two different models with DD model (dotted) and SD model (solid line). Comparison is furthermore made against structures from a TIP4P-POL2 MD simulation (Ref. 35) (dashed). [(a), top] Distribution of angles (H–O–O) with 0° corresponding to a straight H bond, [(b), middle] difference between the H–O–O angles of the two hydrogens on the same molecule indicating the degree of angular asymmetry, and [(c), bottom] difference in shortest O–O distance on the donating side of each molecule indicating the degree of radial asymmetry.
O–O PCFs derived from the RMC fitted DD model and EPSR fits performed by Soper (Ref. 15) of ND data together with either the Hura et al. (Ref. 23) or Narten and Levy (Ref. 37) data sets. In the figure we also show a comparison with structure models obtained from MD simulations using the SPC/E and TIP4P-POL2 (Ref. 35) force fields.
Comparison of calculated total scattering for SPC/E (green), TIP4P-POL2, (blue) and the RMC derived DD structure model (red) with the experimental at from Hura et al. (Ref. 23). The region above has been scaled up by a factor of 5 in the inset to allow a better comparison between measured data and simulations. The molecular scattering factor is also plotted to show its dominant contribution to the scattering intensity.
Comparison of the total structure factor for MD simulations using the SPC/E and TIP4P-POL2 (Ref. 35) force fields and the RMC-DD model with the derived from the experimental data of Hura et al. (Ref. 23). The vertical bars represent the peak position for each oscillation in the experimental and MD obtained .
Resulting E-field distributions from the simultaneous RMC fits to XD and ND data as well as E-field distribution using the (a) DD and (c) asymmetrical models. The reference distribution (b) is taken from a TIP4P-POL2 simulation (Ref. 35).
Decomposition of the E-field distributions into contributions from OH groups in doubly H-bonded (DD) species, H-bonded OH in asymmetric SD species (SD-B), and non-H-bonded OH in asymmetric species (SD-N). ND contributions are small in the DD model and negligible in the asymmetrical SD model. (a) Symmetric DD model and (b) asymmetrical SD model.
Computed XAS spectra for the two different models in comparison with experiment from Ref. 1. (a) Total spectra for the DD and SD models summing 200 and 196 individual spectra, respectively. [(b) and (c)] Individual spectra for the same molecule in the respective dump where the original environment has been modified according to the two different RMC fits. The experimental spectrum has been area normalized to the mean integrated (up to 545 eV) cross section of the two computed sum spectra in A.
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