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Issue 44, 2011
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Wide-angle X-ray diffraction and molecular dynamics study of medium-range order in ambient and hot water

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Abstract

We have developed wide-angle X-ray diffraction measurements with high energy-resolution and accuracy to study water structure at three different temperatures (7, 25 and 66 °C) under normal pressure. Using a spherically curved Ge crystal an energy resolution better than 15 eV has been achieved which eliminates influence from Compton scattering. The high quality of the data allows for a reliable Fourier transform of the experimental data resolving shell structure out to ∼12 Å, i.e. 5 hydration shells. Large-scale molecular dynamics (MD) simulations using the TIP4P/2005 force-field reproduce excellently the experimental shell-structure in the range 4–12 Å although less agreement is seen for the first peak in the intermolecular pair-correlation function (PCF). The Shiratani–Sasai Local Structure Index [J. Chem. Phys. 104, 7671 (1996)] identifies a tetrahedral minority giving the intermediate-range oscillations in the O–O PCF and a disordered majority providing a more featureless background in this range. The current study supports the proposal that the structure of liquid water, even at high temperatures, can be described in terms of a two-state fluctuation model involving local structures related to the high-density and low-density forms of liquid water postulated in the liquid–liquid phase transition hypothesis.

Graphical abstract: Wide-angle X-ray diffraction and molecular dynamics study of medium-range order in ambient and hot water

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Publication details

The article was received on 03 Sep 2011, accepted on 11 Oct 2011 and first published on 19 Oct 2011


Article type: Paper
DOI: 10.1039/C1CP22804H
Citation: Phys. Chem. Chem. Phys., 2011,13, 19997-20007
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    Wide-angle X-ray diffraction and molecular dynamics study of medium-range order in ambient and hot water

    C. Huang, K. T. Wikfeldt, D. Nordlund, U. Bergmann, T. McQueen, J. Sellberg, L. G. M. Pettersson and A. Nilsson, Phys. Chem. Chem. Phys., 2011, 13, 19997
    DOI: 10.1039/C1CP22804H

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