Vanzo Davide, Bratko D, Luzar Alenka
Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284-2006, USA.
J Chem Phys. 2014 Feb 21;140(7):074710. doi: 10.1063/1.4865126.
Electric control of nanopore permeation by water and solutions enables gating in membrane ion channels and can be exploited for transient surface tuning of rugged substrates, to regulate capillary permeability in nanofluidics, and to facilitate energy absorption in porous hydrophobic media. Studies of capillary effects, enhanced by miniaturization, present experimental challenges in the nanoscale regime thus making molecular simulations an important complement to direct measurement. In a molecular dynamics (MD) simulation, exchange of water between the pores and environment requires modeling of coexisting confined and bulk phases, with confined water under the field maintaining equilibrium with the unperturbed environment. In the present article, we discuss viable methodologies for MD sampling in the above class of systems, subject to size-constraints and uncertainties of the barostat function under confinement and nonuniform-field effects. Smooth electric field variation is shown to avoid the inconsistencies of MD integration under abruptly varied field and related ambiguities of conventional barostatting in a strongly nonuniform interfacial system. When using a proper representation of the field at the border region of the confined water, we demonstrate a consistent increase in electrostriction as a function of the field strength inside the pore open to a field-free aqueous environment.
通过水和溶液对纳米孔渗透进行电控制，可实现膜离子通道的门控，并可用于对粗糙基底进行瞬态表面调节、调节纳米流体中的毛细管渗透性以及促进多孔疏水介质中的能量吸收。对因小型化而增强的毛细管效应的研究，在纳米尺度上提出了实验挑战，因此分子模拟成为直接测量的重要补充。在分子动力学（MD）模拟中，孔隙与环境之间的水交换需要对共存的受限相和体相进行建模，其中受限水在电场作用下与未受干扰的环境保持平衡。在本文中，我们讨论了在上述这类系统中进行MD采样的可行方法，该系统受到尺寸限制以及受限和非均匀场效应下恒压器功能的不确定性影响。结果表明，平滑的电场变化可避免在突然变化的场下MD积分的不一致性以及在强非均匀界面系统中传统恒压法的相关模糊性。当在受限水的边界区域使用适当的场表示时，我们证明了对于向无场水环境开放的孔隙，电致伸缩随孔隙内场强的增加而持续增加。
