Institute for Molecular Science, The Graduate University for Advanced Studies, Myodaiji, Okazaki, Aichi 444-8585, Japan.
Indian Institute of Science, Bangalore 560012, India.
J Chem Phys. 2019 Feb 7;150(5):054502. doi: 10.1063/1.5079594.
We investigate thermodynamic properties of supercooled water across the "no man's land" onto the formation of amorphous ice. The calculations are aided by very long computer simulations, often more than 50 μs long, with the TIP4P/2005 model potential. 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 calculations of the quantum mechanical static and frequency-dependent specific heats by combining seminal studies of 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 temperatures. Interestingly, the vibrational entropy lowers the Kauzmann temperature, T, to 130 K, just below the experimental glass-to-liquid water transition temperature, T, of 136 K and the calculated T 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 ∼ 190 K. The calculation of Lindemann ratios shows the melting of amorphous ice ∼135 K. The amorphous state exhibits an extremely short correlation length for the distance dependence of orientational correlation.
我们研究了过冷水中的热力学性质，直至形成非晶冰的“无人区”。这些计算得到了非常长的计算机模拟的辅助，模拟时间通常超过 50μs，使用的是 TIP4P/2005 模型势能。在 228K 附近，由于可能存在液体-液体（LL）转变，密度涨落对水的性质产生了深远的影响，无论是在 LL 转变之上还是之下。我们通过结合 Lebowitz、Percus 和 Verlet 以及 Grest 和 Nagel 的开创性研究以及态密度的谐波近似，对量子力学静态和频率相关比热进行了计算。得到的值与超冷水和冰的比热的所有现有实验和数值结果都非常吻合。我们通过积分比热来计算所有状态点的熵。我们发现，在很宽的温度范围内，分子间振动熵的量子修正贡献主导了非晶相相对于晶体的过剩熵。有趣的是，振动熵降低了 Kauzmann 温度 T，使其降至 130K，略低于实验上玻璃-液态水转变温度 Tg，为 136K，以及我们之前研究中计算的 T，为 135K。然而，从 250K 到低于 250K 的高温熵的直接外推将给出更高的 T 值，约为 190K。 Lindemann 比的计算表明，非晶冰在约 135K 时熔化。非晶态表现出非常短的取向关联距离相关的相关长度。
