Distinct signature of two local structural motifs of liquid water in the scattering function

Abstract

Liquids generally become more ordered upon cooling. However, it has been a long-standing debate on whether such structural ordering in liquid water takes place continuously or discontinuosly: continuum vs. mixture models. Here, by computer simulations of three popular water models and analysis of recent scattering experiment data, we show that, in the structure factor of water, there are two overlapped peaks hidden in the apparent "first diffraction peak", one of which corresponds to the neighboring O-O distance as in ordinary liquids and the other to the longest periodicity of density waves in a tetrahedral structure. This unambiguously proves the coexistence of two local structural motifs. Our findings not only provide key clues to settle long-standing controversy on the water structure but also allow experimental access to the degree and range of structural ordering in liquid water.

arXiv comment24 pages, 18 figures

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• Manifestations of metastable criticality in the long-range structure of model water glasses
• Using Car-Parrinello simulations and microscopic order descriptors to reveal two locally favored structures with distinct molecular dipole moments and dynamics in ambient liquid water
• Revealing the three-component structure of water with principal component analysis (PCA) on X-ray spectrum
• The structural order of protein hydration water
• Competing structures in a minimal double-well potential model of condensed matter