Gaussian and Non-Gaussian Solvent Density Fluctuations within Solute Cavities in a Water-like Solvent
Gaussian and Non-Gaussian Solvent Density Fluctuations within Solute Cavities in a Water-like Solvent
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DOI：
10.1021/acs.jctc.3c00387
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发表时间：
2023-07-12
影响因子：
5.5
通讯作者：
Ashbaugh，Henry S.
中科院分区：
文献类型：
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作者：
Ashbaugh，Henry S.
我们报告了对环境条件下水的粗粒度mW表示中空腔中与长度尺度相关的密度波动的蒙特卡罗模拟研究。具体来说，我们使用测试粒子插入和伞形采样技术相结合，以检查在水中的球形腔的水占领状态的全方位的6.3毫米半径。正如先前所观察到的，水密度波动被发现是有效的高斯性质的原子尺度的腔，但随着腔变得更大，它们表现出非高斯的“肥尾”分布较低的占有状态。我们引入了一种新的统计热力学方法来分析非高斯波动的基础上的径向分布的沃茨的空腔与不同数量的沃茨在其边界。它示出，这些非高斯波动的发病是一个结果的空腔内形成的气泡，因为它是空的，这是伴随着沃茨的吸附到其内表面上。我们重新审视了我们以前介绍的理论框架来描述腔体内的高斯波动，包括表面张力的贡献，将气泡的形成。这个修正后的理论准确地描述了原子和介观尺度空腔内的密度波动。此外，该理论预测的过渡从高斯到非高斯波动在特定的腔占有率，在很好的协议与模拟观察。
We report a Monte Carlo simulation study of length-scale-dependent density fluctuations in cavities in the coarse-grained mW representation of water at ambient conditions. Specifically, we use a combination of test particle insertion and umbrella sampling techniques to examine the full range of water occupation states in spherical cavities up to 6.3 Å radius in water. As has previously been observed, water density fluctuations are found to be effectively Gaussian in nature for atomic-scale cavities, but as the cavities get larger, they exhibit a non-Gaussian “fat-tail” distribution for lower occupancy states. We introduce a new statistical thermodynamic approach to analyze non-Gaussian fluctuations based on the radial distribution of waters about cavities with varying numbers of waters within its boundaries. It is shown that the onset of these non-Gaussian fluctuations is a result of the formation of a bubble within the cavity as it is emptied, which is accompanied by the adsorption of waters onto its interior surface. We revisit a theoretical framework we previously introduced to describe Gaussian fluctuations within cavities to incorporate bubble formation by including surface tension contributions. This modified theory accurately describes density fluctuations within both atomic and meso-scale cavities. Moreover, the theory predicts the transition from Gaussian to non-Gaussian fluctuations at a specific cavity occupancy, in excellent agreement with simulation observations.