Soniat Marielle, Rick Steven W
Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, USA.
J Chem Phys. 2014 May 14;140(18):184703. doi: 10.1063/1.4874256.
Charge transfer (CT), the movement of small amounts of electron density between non-bonded pairs, has been suggested as a driving force for a variety of physical processes. Herein, we examine the effect of CT on ion adsorption to the water liquid-vapor interface. Using a CT force field for molecular dynamics, we construct a potential of mean force (PMF) for Na(+), K(+), Cl(-), and I(-). The PMFs were produced with respect to an average interface and an instantaneous interface. An analysis of the PMF relative to the instantaneous surface reveals that the area in which the anions experience a free energy minimum is quite narrow, and the cations feel a steeply repulsive free energy near the interface. CT is seen to have only minor effects on the overall free energy profiles. However, the long-ranged effects of ions are highlighted by the CT model. Due to CT, the water molecules at the surface become charged, even when the ion is over 15 Å away from the surface.
电荷转移（CT），即非键合电子对之间少量电子密度的移动，已被认为是多种物理过程的驱动力。在此，我们研究电荷转移对离子吸附到水液 - 气界面的影响。使用用于分子动力学的电荷转移力场，我们构建了Na(+)、K(+)、Cl(-)和I(-)的平均力势（PMF）。这些PMF是相对于平均界面和瞬时界面生成的。相对于瞬时表面的PMF分析表明，阴离子经历自由能最小值的区域相当狭窄，而阳离子在界面附近感受到强烈的排斥自由能。电荷转移对整体自由能分布的影响较小。然而，电荷转移模型突出了离子的长程效应。由于电荷转移，即使离子距离表面超过15 Å，表面的水分子也会带电。
