Virtual-Wall Model for Molecular Dynamics Simulation.

A large number of molecules are usually required to model atomic walls in molecular dynamics simulations. A virtual-wall model is proposed in this study to describe fluid-wall molecular interactions, for reducing the computational time. The infinite repetition of unit cell structures within the atomic wall causes the periodicity of the force acting on a fluid molecule from the wall molecules. This force is first calculated and then stored in the memory. A fluid molecule appearing in the wall force field is subjected to the force from the wall molecules. The force can then be determined by the position of the molecule relative to the wall. This model avoids excessive calculations of fluid-wall interactions and reduces the computational time drastically. The time reduction is significant for small fluid density and channel height. The virtual-wall model is applied to Poiseuille and Couette flows, and to a flow in a channel with a rough surface. Results of the virtual and atomic wall simulations agree well with each other, thereby indicating the usefulness of the virtual-wall model. The appropriate bin size and cut-off radius in the virtual-wall model are also discussed.

在分子动力学模拟中，通常需要大量分子来模拟原子壁。本研究提出一种虚拟壁模型来描述流体 - 壁分子间的相互作用，以减少计算时间。原子壁内晶胞结构的无限重复导致壁分子对流体分子作用力的周期性。首先计算该力，然后将其存储在内存中。出现在壁力场中的流体分子会受到来自壁分子的力。然后可以根据分子相对于壁的位置确定该力。该模型避免了对流体 - 壁相互作用的过度计算，并大幅减少了计算时间。对于较小的流体密度和通道高度，时间减少效果显著。将虚拟壁模型应用于泊肃叶流和库埃特流，以及粗糙表面通道中的流动。虚拟壁和原子壁模拟的结果彼此吻合良好，从而表明虚拟壁模型的有效性。还讨论了虚拟壁模型中合适的箱尺寸和截断半径。