# Unravelling the contribution of local structures to the anomalies of water: the synergistic action of several factors

## TL;DR

This study uses molecular dynamics simulations to explore how local structural changes in water's hydrogen bond network contribute to its anomalous properties, especially near the Widom line and under different pressures.

## Contribution

It provides a detailed microscopic analysis of water's anomalies, highlighting the role of LDL and HDL environments and their spatial organization, revealing the synergistic factors involved.

## Key findings

- HDL-like clusters fragment at a critical LDL concentration of 20-30%.
- The hydrogen bond network in LDL environments shows maximal frustration with pentagonal and hexagonal rings.
- Global order decreases near the Widom line, supporting the liquid-liquid critical point hypothesis.

## Abstract

We investigate the microscopic origin of water's anomalies by inspecting the hydrogen bond network (HBN) and the spatial organization of low-density-liquid (LDL) like and high-density-liquid (HDL) like environments. Specifically, we simulate --via classical molecular dynamics simulations-- the isobaric cooling of a sample composed by 512 water molecules from ambient to deeply undercooled conditions at three pressures, namely 1 bar, 400 bar and 1000 bar. \emph{In correspondence with the Widom line}, (i) the HDL-like dominating cluster undergoes fragmentation caused by the percolation of LDL-like aggregates following a spinodal-like kinetics; (ii) such fragmentation always occur s at a "critical" concentration of $\sim20-30\%$ in LDL; (iii) the HBN within LDL-like environments is characterized by an equal number of pentagonal and hexagonal rings that create a state of maximal frustration between a configuration that promotes crystallization (hexagonal ring) and a configuration that hinders it (pentagonal ring); (iv) the spatial organization of HDL-like environments shows a marked variation. Moreover, the inspection of the global symmetry shows that the intermediate-range order decreases in correspondence with the Wid om line, and such decrease becomes more pronounced upon increasing the pressure, hence supporting the hypothesis of a liquid-liquid critical point. Our results reveal and rationalize the complex microscopic origin of water's anomalies as the cooperative effect of several fac tors acting synergistically. Beyond implications for water, our findings may be extended to other materials displaying anomalous behaviours.