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首页> 外文期刊>The Journal of Chemical Physics >An exact method to obtain effective electrostatic interactions from computer simulations: The case of effective charge amplification
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An exact method to obtain effective electrostatic interactions from computer simulations: The case of effective charge amplification

机译：从计算机仿真中获得有效静电相互作用的精确方法：有效电荷放大的情况

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摘要

We discuss here an exact method to determine the parameters regulating the screened Coulomb interactions among spherical macroions immersed in a simple electrolyte. This approach provides rigorous definitions for the corresponding screening length, effective permittivity, and renormalized charges, and can be employed for precise and reliable calculations of these parameters within any scheme. In particular, we introduce a simple procedure for extracting this information from computer simulations. The viability of this approach is demonstrated by applying it to a three-component model system which includes anionic nanoparticles and monovalent cations and anions. The mean forces between nanoparticles are determined directly from simulations with two macroions, plus small ions, inside a single cell with periodic boundary conditions. The values of the parameters of interest, on the other hand, are gathered from two separate sets of computer simulations: one set provides information about the short-range correlations among the small ions, which in turn determine the screening length and effective permittivity; the second set supplies the short-range components of the ionic distribution around one isolated macroion, which also determine its renormalized charge. The method presented here thus avoids the uncertain fitting of these parameters from the asymptotic tail of the mean force and allows us to investigate in detail this connection between the renormalized charge of themacroion and the short-range (virtual) part of the ionic cloud surrounding it. Using the standard prescription to extract an effective charge from the corresponding renormalized value, we then proceed to clarify the mechanisms behind the possibility of effective charge amplification (i.e., an effective charge larger than the bare macroion charge). Complementarily, we report results for the corresponding bridge functions too.
机译：我们在这里讨论一种确定确定调节浸没在简单电解质中的球形大分子之间的库仑相互作用的参数的精确方法。这种方法为相应的筛选长度，有效介电常数和重新归一化的电荷提供了严格的定义，并且可以在任何方案中用于这些参数的精确可靠的计算。特别是，我们介绍了一种从计算机模拟中提取此信息的简单过程。通过将其应用于包含阴离子纳米粒子以及一价阳离子和阴离子的三组分模型系统，可以证明该方法的可行性。纳米粒子之间的平均力直接由具有周期性边界条件的单个单元内的两个大离子加上小离子的模拟直接确定。另一方面，感兴趣的参数值是从两套单独的计算机模拟中收集的：一组提供有关小离子之间短程相关性的信息，这些信息反过来又决定了屏蔽长度和有效介电常数。第二组提供一个孤立的大分子周围离子分布的短程分量，这也决定了其重新归一化的电荷。因此，此处介绍的方法避免了平均力的渐近尾部对这些参数的不确定拟合，并允许我们详细研究重塑宏膜的归一化电荷与其周围离子云的短距离（虚拟）部分之间的关​​系。 。然后使用标准处方从相应的重新归一化的值中提取有效电荷，然后继续阐明有效电荷放大的可能性（即，有效电荷大于裸宏离子电荷）背后的机制。作为补充，我们也报告相应桥功能的结果。

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