Elton Daniel C
Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA.
Phys Chem Chem Phys. 2017 Jul 19;19(28):18739-18749. doi: 10.1039/c7cp02884a.
We critically review the literature on the Debye absorption peak of liquid water and the excess response found on the high frequency side of the Debye peak. We find a lack of agreement on the microscopic phenomena underlying both of these features. To better understand the molecular origin of Debye peak we ran large scale molecular dynamics simulations and performed several different distance-dependent decompositions of the low frequency dielectric spectra, finding that it involves processes that take place on scales of 1.5-2.0 nm. We also calculated the k-dependence of the Debye relaxation, finding it to be highly dispersive. These findings are inconsistent with models that relate Debye relaxation to local processes such as the rotation/translation of molecules after H-bond breaking. We introduce the spectrumfitter Python package for fitting dielectric spectra and analyze different ways of fitting the high frequency excess, such as including one or two additional Debye peaks. We propose using the generalized Lydanne-Sachs-Teller (gLST) equation as a way of testing the physicality of model dielectric functions. Our attempts at fitting the experimental spectrum using the gLST relation as a constraint indicate that the traditional way of fitting the excess response with secondary and tertiary Debye relaxations is problematic. All of our work is consistent with the recent theory of Popov et al. (2016) that Debye relaxation is due to the migration of Bjerrum-like defects in the hydrogen bond network. Under this theory, the mechanism of Debye relaxation in liquid water is similar to the mechanism in ice, but the heterogeneity and power-law dynamics of the H-bond network in water results in excess response on the high frequency side of the peak.
我们批判性地回顾了关于液态水德拜吸收峰以及在德拜峰高频侧发现的过量响应的文献。我们发现对于这两个特征背后的微观现象缺乏共识。为了更好地理解德拜峰的分子起源，我们进行了大规模分子动力学模拟，并对低频介电谱进行了几种不同的距离相关分解，发现它涉及发生在1.5 - 2.0纳米尺度上的过程。我们还计算了德拜弛豫的k依赖性，发现它具有高度色散性。这些发现与将德拜弛豫与局部过程（如氢键断裂后分子的旋转/平移）相关联的模型不一致。我们引入了用于拟合介电谱的spectrumfitter Python包，并分析了拟合高频过量的不同方法，例如包括一个或两个额外的德拜峰。我们建议使用广义Lydanne - Sachs - Teller（gLST）方程作为检验模型介电函数物理性的一种方法。我们尝试使用gLST关系作为约束来拟合实验谱，结果表明用二级和三级德拜弛豫来拟合过量响应的传统方法存在问题。我们所有的工作都与波波夫等人（2016年）的最新理论一致，即德拜弛豫是由于氢键网络中类比耶鲁姆缺陷的迁移。在该理论下，液态水中德拜弛豫的机制与冰中的机制相似，但水中氢键网络的不均匀性和幂律动力学导致了峰高频侧的过量响应。
