Frequency dependence of specific heat in supercooled liquid water and emergence of correlated dynamics.
Frequency dependence of specific heat in supercooled liquid water and emergence of correlated dynamics.
复制标题
过冷液态水中比热的频率依赖性和相关动力学的出现。
DOI：
10.1063/1.4793555
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
B. Bagchi
中科院分区：
文献类型：
--
作者：
S. Saito;I. Ohmine;B. Bagchi
本文通过大量的计算机模拟和理论分析，研究了过冷液态水比热异常的分子起源。模拟结果表明，等压比热随温度的降低而急剧增加，而等容比热在同一温度范围内随温度的变化不大。我们计算了温度涨落之间的时空相关性，并研究了比热随频率的变化。当温度低于270 K时，后者在低频区表现出快速增长。为了理解这种增加的微观基础，我们已经进行了一个shellwise分解的贡献，遥远的分子在中心分子的温度波动。这种分解揭示了出现，在低温下，时间上缓慢，空间上长范围的大的温度波动。温度波动时间相关函数（TFCF）可以拟合为William-Watts拉伸指数形式，在低温下拉伸参数接近0.6，表明高度非指数弛豫。相关函数的弛豫时间的温度依赖性可以拟合到Vogel-Fulcher-Tamermann表达式，该表达式提供了液体脆性的定量测量。有趣的是，我们发现TFCF的弛豫时间随着温度的降低而快速增长，在220 K附近经历了一个从显着脆性状态到弱脆性状态的急剧交叉。
Molecular origin of the well-known specific heat anomaly in supercooled liquid water is investigated here by using extensive computer simulations and theoretical analyses. A rather sharp increase in the values of isobaric specific heat with lowering temperature and the weak temperature dependence of isochoric specific heat in the same range are reproduced in simulations. We calculated the spatio-temporal correlation among temperature fluctuations and examined the frequency dependent specific heat. The latter shows a rapid growth in the low frequency regime as temperature is cooled below 270 K. In order to understand the microscopic basis of this increase, we have performed a shellwise decomposition of contributions of distant molecules to the temperature fluctuations in a central molecule. This decomposition reveals the emergence, at low temperatures, of temporally slow, spatially long ranged large temperature fluctuations. The temperature fluctuation time correlation function (TFCF) can be fitted to a William-Watts stretched exponential form with the stretching parameter close to 0.6 at low temperatures, indicating highly non-exponential relaxation. Temperature dependence of the relaxation time of the correlation function can be fitted to Vogel-Fulcher-Tamermann expression which provides a quantitative measure of the fragility of the liquid. Interestingly, we find that the rapid growth in the relaxation time of TFCF with lowering temperature undergoes a sharp crossover from a markedly fragile state to a weakly fragile state around 220 K.
影响因子：
4.4
作者：
Abascal, JLF;Vega, C
通讯作者：
Vega, C