Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, 19716.
Department of Chemistry, Indian Institute of Technology Ropar, Ropar, 140001, India.
J Comput Chem. 2017 Jun 15;38(16):1389-1409. doi: 10.1002/jcc.24789.
Conventional classical force fields by construction do not explicitly partition intermolecular interactions to include polarization and charge transfer effects, whereas fully quantum mechanical treatments allow a means to effect this dissection (although not uniquely due to the lack of a charge transfer operator). Considering the importance of polarization in a variety of systems, a particular class of classical models, charge equilibration models, have been extensively developed to study those systems; since these types of interaction models are inherently based on movement of charge throughout a system, they are natural platform for including polarization and charge transfer effects within the context of molecular simulations. Here, we present two bond-space charge equilibration models we term as QE2 and mixed QE2 treat charge transfer in classical molecular mechanical calculations those provide practical solutions to two major drawbacks of charge equilibration models: (a) a nonvanishing amount of charge transfer between two heteroatoms at large separations, and (b) superlinear polarizability scaling during bond dissociation due to charge transfer over unphysical, large distances. To control charge transfer during dissociation of a bond in a molecular system, we introduce a distance-dependent scaling function (QE2 model) which, controls and recovers physical behavior of the homonuclear and heteronuclear charge transfer between two atoms at small and large values of internuclear separation; and the mixed QE2 model in which we combine the QE2 model under allow and disallow charge transfer situations that describe both charge transfer and polarizability in a distance-dependent manner. We demonstrate the utility of both models in the case of a water dimer, and compare the results with other existing models, and further, we perform short molecular dynamics simulations for few water clusters with the QE2 model to show the charge transfer and internuclear separation are correlated in dynamics. © 2017 Wiley Periodicals, Inc.
传统的经典力场在构建时并没有明确地将分子间相互作用分割开来，以包括极化和电荷转移效应，而全量子力学处理方法则提供了一种实现这种分割的手段（尽管由于缺乏电荷转移算子，这种分割不是唯一的）。考虑到极化在各种系统中的重要性，已经广泛开发了一类特殊的经典模型，即电荷平衡模型，以研究这些系统；由于这些类型的相互作用模型本质上是基于电荷在整个系统中的移动，因此它们是在分子模拟中包含极化和电荷转移效应的自然平台。在这里，我们提出了两种键空间电荷平衡模型，我们称之为 QE2 和混合 QE2，它们在经典分子力学计算中处理电荷转移问题，为电荷平衡模型的两个主要缺点提供了实际解决方案：（a）在两个杂原子之间的大分离处存在非零的电荷转移，（b）由于电荷在不真实的大距离上转移，键解离过程中的极化率呈超线性增长。为了控制分子系统中键解离过程中的电荷转移，我们引入了一个距离相关的缩放函数（QE2 模型），该函数控制和恢复了同核和异核之间两个原子在小和大核间距处的电荷转移的物理行为；混合 QE2 模型中，我们在允许和不允许电荷转移的情况下结合了 QE2 模型，以距离相关的方式描述电荷转移和极化率。我们在水二聚体的情况下演示了这两种模型的实用性，并将结果与其他现有模型进行了比较，进一步，我们使用 QE2 模型对几个水分子簇进行了短时间的分子动力学模拟，以显示电荷转移和核间距在动力学上是相关的。©2017 年 Wiley 期刊，Inc.
