On the Range of Water Structure Models Compatible with X-ray and Neutron Diffraction Data

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• 作者：Kjartan T. Wikfeldt ; Mikael Leetmaa ; Mathias P. Ljungberg ; Anders Nilsson ; Lars G. M. Pettersson
• 刊名：Journal of Physical Chemistry B
• 出版年：2009
• 出版时间：May 7, 2009
• 年：2009
• 卷：113
• 期：18
• 页码：6246-6255
• 全文大小：310K
• 年卷期：v.113,no.18(May 7, 2009)
• ISSN：1520-5207

文摘

We use the reverse Monte Carlo (RMC) method to critically evaluate the structural information content of diffraction data on bulk water by fitting simultaneously or separately to X-ray and neutron data; the O−H and H−H, but not the O−O, pair-correlation functions (PCFs) are well-described by the neutron data alone. Enforcing at the same time different H-bonding constraints, we generate four topologically different structure models of liquid water, including a simple mixture model, that all equally well reproduce the diffraction data. Although earlier work [Leetmaa, M.; et al. J. Chem. Phys. 2008, 129, 084502] has focused on tetrahedrality in the H-bond network in liquid water, we show here that, even for the O−O−O three-body correlation, tetrahedrality is not strictly defined by the data. We analyze how well two popular MD models (TIP4P-pol2 and SPC/E) reproduce the neutron data in q-space and find differences in important aspects from the experiment. From the RMC fits, we obtain pair-correlation functions (PCFs) that are in optimal agreement with the diffraction data but still show a surprisingly strong variability both in position and height of the first intermolecular (H-bonding) O−H peak. We conclude that, although diffraction data impose important constraints on the range of possible water structures, additional data are needed to narrow the range of possible structure models.