Frequency and wave-vector dependent dielectric function of water: Collective modes and relaxation spectral
Frequency and wave-vector dependent dielectric function of water: Collective modes and relaxation spectral
复制标题
DOI：
10.1063/1.476884
复制
发表时间：
1998-08-01
影响因子：
4.4
通讯作者：
Sutmann, G
中科院分区：
文献类型：
--
作者：
Bopp, PA;Kornyshev, AA;Sutmann, G
在较宽的k值范围内，利用分子动力学方法对水的中心力模型进行了计算机模拟，计算了纵向频率和波矢量相关的复介电响应函数chi(k, omega) = 1 - 1/epsilon（k, omega）。它的虚部，即Im{E(k,)}//epsilon(k,)/(2)，在小k值区域表现出两个主要贡献：下层的类德拜取向弛豫；频谱的频率部分和高频翼处的阻尼振动共振。德拜弛豫时间不遵循类似德格涅斯的模式：tau(k)在k近似于k*近似于1.7埃（-1）时达到最大值，而静态极性结构因子S(k)在k近似于3埃（-1）时达到峰值。谐振频率ω (k)和衰减衰减量γ (k)呈现色散规律，表明其为类光学衰减模式；自由子。用近似正模方法，我们在分子水平上分析了这种模式的起源，表明它是由于分子取向的阻尼传播。通过氢网络的振动；债券。在高k时，由于集体运动耗散成单粒子运动，衰变占主导地位。在响应函数谱的基础上，利用Kramers-Kronig关系计算了静态介电函数。在小k区域，epsilon(k)从宏观值E近似于80减小到近似于15，即它表现出洛伦兹型行为。这种行为是由高阶多极相关函数决定的。在中间和高k范围内，我们关于epsilon(k)和chi(k)的结果与从实验偏对相关函数中提取的数据非常吻合：epsilon(k)在k轴上显示两个发散点，其范围为负值，在chi(k)中发现最大值：chi(max)(k)远大于1，表明过度筛选。讨论了chi(k)的量子修正对纯经典计算的影响，并给出了水合离子间相互作用能的结果。(C) 1998美国物理研究所。
The longitudinal frequency and wave-vector dependent complex dielectric response function chi(k, omega) = 1 - 1/epsilon(k, omega) is calculated in a broad range of k values-by means of molecular dynamics computer simulation for a central force model of water. Its imaginary part, i.e., Im{E(k, omega)}//epsilon(k, omega)/(2), shows two main contributions in the region of small k values: Debye-like orientational relaxation in the-lower;frequency part of the spectrum and a damped librational resonance at the high frequency wing. The Debye relaxation time does not follow a de Gennes-like pattern: tau(k) goes through a maximum at k approximate to k* approximate to 1.7 Angstrom(-1), while the static polar structure factor S(k) peaks at k approximate to 3 Angstrom(-1). The resonance frequency omega(k) and the decay decrement gamma(k) show a dispersion law, indicative of a decaying optical-like mode; the libron. With an approximate normal mode approach, we analyze the origin of this mode on a molecular level which shows that it is due to a damped propagation of molecular orientational. vibrations through the network of hydrogen; bonds. At high k the decay, due to dissipation of collective into single particle motions, dominates. The static dielectric function is calculated on the basis of the response function spectra via the Kramers-Kronig relation. In the small k region epsilon(k) decreases from the macroscopic value E approximate to 80 to a value approximate to 15, i.e. it exhibits a Lorentzian-type behavior. This behavior is shown to be determined by higher order multipole correlation functions. In the intermediate and high k range, our results on epsilon(k) and chi(k) are in excellent agreement with data extracted from experimental partial pair correlation functions: epsilon(k) exhibits two divergence points on the k axis with a range of negative, values in between where a maximum in chi(k) is found: with chi(max)(k) much greater than 1, indicative-of overscreening. Consequences of quantum corrections to chi(k) with respect to a purely classical calculation are discussed and consequences are shown for the interaction energy between hydrated ions. (C) 1998 American Institute of Physics.