Liquid-liquid phase transition in simulations of ultrafast heating and decompression of amorphous ice

TL;DR

This study uses computer simulations of the ST2 water model to demonstrate that a liquid-liquid phase transition in supercooled water can be detected during ultrafast heating and decompression of amorphous ice, aligning with recent experimental findings.

Contribution

The paper shows that signatures of the liquid-liquid phase transition can be observed in out-of-equilibrium conditions similar to recent experiments, providing computational support for the experimental claims.

Findings

Detection of LLPT signatures during ultrafast heating and decompression.

Consistency with previous phase diagram studies of glassy ST2 water.

Validation of the experimental protocol through simulation results.

Abstract

A recent experiment [K. H. Kim, et al., Science 370, 978 (2020)] showed that it may be possible to detect a liquid-liquid phase transition (LLPT) in supercooled water by subjecting high density amorphous ice (HDA) to ultrafast heating, after which the sample reportedly undergoes spontaneous decompression from a high density liquid (HDL) to a low density liquid (LDL) via a first-order phase transition. Here we conduct computer simulations of the ST2 water model, in which a LLPT is known to occur. We subject various HDA samples of this model to a heating and decompression protocol that follows a thermodynamic pathway similar to that of the recent experiments. Our results show that a signature of the underlying equilibrium LLPT can be observed in a strongly out-of-equilibrium process that follows this pathway despite the very high heating and decompression rates employed here. Our results are also consistent with the phase diagram of glassy ST2 water reported in previous studies.