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arXiv · 1511.01959

Density and bond-orientational relaxations in supercooled water

Jeremy C. Palmer·Rakesh S. Singh·Renjie Chen·Fausto Martelli·Pablo G. Debenedetti
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Abstract

Recent computational studies have reported evidence of a metastable liquid-liquid phase transition (LLPT) in molecular models of water under deeply supercooled conditions. A competing hypothesis suggests, however, that non-equilibrium artifacts associated with coarsening of the stable crystal phase have been mistaken for an LLPT in these models. Such artifacts are posited to arise due to a separation of time scales in which density fluctuations in the supercooled liquid relax orders of magnitude faster than those associated with bond-orientational order. Here, we use molecular simulation to investigate the relaxation of density and bond-orientational fluctuations in three molecular models of water (ST2, TIP5P and TIP4P/2005) in the vicinity of their reported LLPT. For each model, we find that density is the slowly relaxing variable under such conditions. We also observe similar behavior in the coarse-grained mW model of water. Our findings therefore challenge the key physical assumption underlying the competing hypothesis.e find that density relaxes significantly faster than bond-orientational order, as incorrectly predicted by this competing hypothesis.

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Jeremy C. Palmer, Rakesh S. Singh, Renjie Chen, Fausto Martelli, Pablo G. Debenedetti. 2015-11-06. Density and bond-orientational relaxations in supercooled water. https://doi.org/10.1080/00268976.2016.1179351

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