Non-Gaussian statistics of electrostatic fluctuations of hydration shells
Non-Gaussian statistics of electrostatic fluctuations of hydration shells
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DOI：
10.1063/1.3633478
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发表时间：
2011-09-14
影响因子：
4.4
通讯作者：
Matyushov, Dmitry V.
中科院分区：
文献类型：
--
作者：
Friesen, Allan D.;Matyushov, Dmitry V.
本文的目的是了解由水界面的非极性溶质纳米尺寸的电场的统计。我们研究，通过数值模拟，SPC/E水和Kihara溶质，这是一个硬球的核心与Lennard-Jones层在其表面之间的接口。的界面电场的分布监测作为一个函数的大小的一个点偶极子放置在靠近溶质-水界面。自由能表面作为在偶极方向上投影的电场的函数，随着偶极幅度的增加而显示出交叉。虽然它是一个单井谐波函数在低偶极值，它成为一个双井表面在中间的偶极矩幅度，再次转化为一个单井表面，具有非零的最小位置，在更高的偶极。这种转变，让人想起在散装材料的不连续相变，有一个广泛的中间区域，界面沃茨波动之间的两个最小值。该区域的特点是强烈的场波动，与非高斯统计和方差远远超出预期的线性响应近似。表面水的激发态被发现被解除基态以上所需的能量，以打破约两个氢键。这种状态被溶质偶极的外部电场拉低能量，使其容易受到热激发。激发态是氢键网络中的表面缺陷，在附近的网络中产生应力，但在最接近溶质偶极子的区域中相对局部化。(C)2011年美国物理学会。[doi：10.1063/1.3633478]
This paper aims to understand the statistics of the electric field produced by water interfacing a non-polar solute of nanometer dimension. We study, by numerical simulations, the interface between SPC/E water and a Kihara solute, which is a hard-sphere core with a Lennard-Jones layer at its surface. The distribution of the interfacial electric field is monitored as a function of the magnitude of a point dipole placed close to the solute-water interface. The free energy surface as a function of the electric field projected on the dipole direction shows a cross-over with increasing dipole magnitude. While it is a single-well harmonic function at low dipole values, it becomes a double-well surface at intermediate dipole moment magnitudes, transforming into a single-well surface again, with a non-zero minimum position, at still higher dipoles. This transformation, reminiscent of a discontinuous phase transition in bulk materials, has a broad intermediate region where the interfacial waters fluctuate between the two minima. This region is characterized by intense field fluctuations, with non-Gaussian statistics and variance far exceeding expectations from the linear-response approximation. The excited state of the surface water is found to be lifted above the ground state by the energy required to break approximately two hydrogen bonds. This state is pulled down in energy by the external electric field of the solute dipole, making it readily accessible to thermal excitations. The excited state is a surface defect in the hydrogen-bond network, creating a stress in the nearby network, but otherwise relatively localized in the region closest to the solute dipole. (C) 2011 American Institute of Physics. [doi:10.1063/1.3633478]