Joseph Sony, Aluru N R
Department of Mechanical Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Langmuir. 2006 Oct 10;22(21):9041-51. doi: 10.1021/la0610147.
Effects of nanoscale confinement and partial charges that stem from quantum calculations are investigated in silica slit channels filled with 1 M KCl at the point of zero charge by using a hierarchical multiscale simulation methodology. Partial charges of both bulk and surface atoms from ab initio quantum calculations that take into account bond polarization and electronegativity are used in molecular dynamics (MD) simulations to obtain ion and water concentration profiles for channel widths of 1.1, 2.1, 2.75, and 4.1 nm. The interfacial electron density profiles of simulations matched well with that of recent X-ray reflectivity experiments. By simulating corresponding channels with no partial charges, it was observed that the partial charges affect the concentration profiles and transport properties such as diffusion coefficients and mobilities up to a distance of about 3 sigma(O)(-)(O) from the surface. Both in uncharged and partially charged cases, oscillations in concentration profiles of K(+) and Cl(-) ions give rise to an electro-osmotic flow in the presence of an external electric field, indicating the presence of an electric double layer at net zero surface charge, contrary to the expectations from classical continuum theory. I-V curves in a channel-bath system using ionic mobilities from MD simulations were significantly different for channels with and without partial charges for channel widths less than 4.1 nm.
通过使用分层多尺度模拟方法，研究了在零电荷点填充1 M KCl的二氧化硅狭缝通道中，源于量子计算的纳米尺度限制和部分电荷的影响。在分子动力学（MD）模拟中，使用考虑键极化和电负性的从头算量子计算得到的体相和表面原子的部分电荷，以获得通道宽度为1.1、2.1、2.75和4.1 nm时的离子和水浓度分布。模拟的界面电子密度分布与最近的X射线反射率实验结果匹配良好。通过模拟没有部分电荷的相应通道，观察到部分电荷会影响浓度分布和传输性质，如扩散系数和迁移率，影响范围可达距表面约3个氧离子直径的距离。在无电荷和有部分电荷的情况下，钾离子和氯离子浓度分布的振荡在存在外部电场时都会引起电渗流，这表明在净零表面电荷处存在双电层，这与经典连续介质理论的预期相反。对于通道宽度小于4.1 nm的通道，使用MD模拟得到的离子迁移率的通道-浴系统中的电流-电压（I-V）曲线，有部分电荷和无部分电荷的情况有显著差异。
