3 years ago

Exploration of vitrification of water and Kauzmann entropy through complex specific heat: A journey through 'No Man's Land'.

Shinji Saito, Biman Bagchi

Frequency dependent specific heat, introduced by Grest and Nagel, offers valuable insight into the vitrification of supercooled liquid. We calculate this quantity and other thermodynamic properties of supercooled liquid water by varying temperature and density across the "no man's land" all the way to the formation of amorphous ice. The calculations are aided by very long computer simulations, often more than 50 $\mu s$ long. Density fluctuations that arise from the proximity to a putative liquid-liquid (LL) transition at 228 K, cast a long shadow on the properties of water, both above and below the LL transition. We carry out the calculation of the quantum mechanical static and frequency-dependent specific heats by combining seminal works by Lebowitz, Percus, and Verlet and Grest and Nagel with the harmonic approximation for the density of states. The obtained values are in quantitative agreement with all available experimental and numerical results of specific heats for both supercooled water and ice. We calculate the entropy at all the state points by integrating the specific heat. We find that the quantum corrected-contributions of intermolecular vibrational entropy dominate the excess entropy of amorphous phases over the crystal over a wide range of temperature. Interestingly, the vibrational entropy lowers the Kauzmann temperature, $T_{\rm K}$, to 130 K, just below the experimental glass-to-liquid water transition temperature, $T_{\rm g}$, of 136 K and the calculated $T_{\rm g}$ of 135 K in our previous study. A straightforward extrapolation of high temperature entropy from 250 K to below however would give a much higher value of $T_{\rm K}$ $\sim$ 190 K. The calculation of Lindemann ratios places the melting of amorphous ice $\sim$ 135 K. The amorphous state exhibits an extremely short correlation length for the distance dependence of orientational correlation.

Publisher URL: http://arxiv.org/abs/1811.05643

DOI: arXiv:1811.05643v1

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