Department of Chemistry, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578, Japan.
J Chem Phys. 2018 Apr 7;148(13):134119. doi: 10.1063/1.5019874.
It is a promising extension of the quantum mechanical/molecular mechanical (QM/MM) approach to incorporate the solvent molecules surrounding the QM solute into the QM region to ensure the adequate description of the electronic polarization of the solute. However, the solvent molecules in the QM region inevitably diffuse into the MM bulk during the QM/MM simulation. In this article, we developed a simple and efficient method, referred to as the "boundary constraint with correction (BCC)," to prevent the diffusion of the solvent water molecules by means of a constraint potential. The point of the BCC method is to compensate the error in a statistical property due to the bias potential by adding a correction term obtained through a set of QM/MM simulations. The BCC method is designed so that the effect of the bias potential completely vanishes when the QM solvent is identical with the MM solvent. Furthermore, the desirable conditions, that is, the continuities of energy and force and the conservations of energy and momentum, are fulfilled in principle. We applied the QM/MM-BCC method to a hydronium ion(HO) in aqueous solution to construct the radial distribution function (RDF) of the solvent around the solute. It was demonstrated that the correction term fairly compensated the error and led the RDF in good agreement with the result given by an ab initio molecular dynamics simulation.
将溶剂分子纳入 QM 区域以充分描述溶质的电子极化，这是对量子力学/分子力学（QM/MM）方法的一种很有前景的扩展。然而，在 QM/MM 模拟过程中，QM 区域中的溶剂分子不可避免地会扩散到 MM 本体中。在本文中，我们开发了一种简单有效的方法，称为“带修正的边界约束（BCC）”，通过约束势来防止溶剂水分子的扩散。BCC 方法的要点是通过添加通过一组 QM/MM 模拟获得的校正项来补偿偏置势引起的统计性质中的误差。BCC 方法的设计使得当 QM 溶剂与 MM 溶剂相同时，偏置势的影响完全消失。此外，原则上满足能量和力的连续性以及能量和动量的守恒性等理想条件。我们将 QM/MM-BCC 方法应用于水溶液中的水合氢离子（HO），以构建溶剂在溶质周围的径向分布函数（RDF）。结果表明，校正项很好地补偿了误差，使 RDF 与从头算分子动力学模拟的结果非常吻合。
