Topological origin of peak splitting in the structure factor of liquid water

TL;DR

This paper demonstrates that the peak splitting in liquid water's structure factor originates from medium-range topological features of its hydrogen-bond network, specifically the distribution of ring sizes.

Contribution

It reveals that topological ring structures, especially 5-8-membered rings, explain the peak splitting, linking network topology to diffraction features.

Findings

5-8-membered rings dominate water's network topology at low temperatures

5-membered rings maintain structural signatures above room temperature

Topological features directly explain the bimodal scattering signal

Abstract

The splitting of the principal peak in the structure factor of liquid water is commonly interpreted as evidence of a competition between two distinct local environments. Here, we show that this peak splitting arises from medium-range topological features of the hydrogen-bond network. Using atomistic simulations, we systematically decompose the structure factor into contributions from hydrogen-bonded rings of different sizes. We find that 5-8-membered rings, which dominate the network topology of liquid water at low temperatures, can directly explain the experimentally observed bimodal scattering signal. Among these, 5-membered rings are particularly persistent, maintaining distinct structural signatures even above room temperature. Our findings establish a direct link between the network topology of liquid water and experimentally accessible diffraction features, clarifying the microscopic basis of water's behaviour and suggesting a broader conceptual framework for interpreting the anomalies in tetrahedral network liquids and glasses.