School of Science , University of New South Wales, Canberra , Canberra ACT 2600 , Australia.
Department of Theoretical Chemistry, Chemical Centre , Lund University P. O. Box 124, S-22100 Lund , Sweden.
J Chem Theory Comput. 2019 Dec 10;15(12):6944-6957. doi: 10.1021/acs.jctc.9b00804. Epub 2019 Nov 18.
We describe a new grand canonical Monte Carlo method to treat fluids in pores in chemical equilibrium with a reference bulk. The method is applied to Lennard-Jones particles in pores of different geometry and is shown to be much more accurate and efficient than other techniques such as traditional grand canonical simulations or Widom's particle insertion method. It utilizes a penalty potential to create a gas phase, which is in equilibrium with a more dense liquid component in the pore. Grand canonical Monte Carlo moves are employed in the gas phase, and the system then maintains chemical equilibrium by "diffusion" of particles. This creates an interface, which means that the confined fluid needs to occupy a large enough volume so that this is not an issue. We also applied the method to confined charged fluids and show how it can be used to determine local electrostatic potentials in the confined fluid, which are properly referenced to the bulk. This precludes the need to determine the Donnan potential (which controls electrochemical equilibrium) explicitly. Prior approaches have used explicit bulk simulations to measure this potential difference, which are significantly costly from a computational point of view. One outcome of our analysis is that pores of finite cross-section create a potential difference with the bulk via a small but nonzero linear charge density, which diminishes as ∼1/ln(), where is the pore length.
我们描述了一种新的巨正则蒙特卡罗方法，用于处理与参考体处于化学平衡的多孔中的流体。该方法适用于不同几何形状的孔中的 Lennard-Jones 粒子，并且比其他技术（例如传统的巨正则模拟或 Widom 的粒子插入法）更加准确和高效。它利用罚函数势来创建气相，该气相与孔中的更密集的液相组分处于平衡状态。在气相中使用巨正则蒙特卡罗移动，然后通过粒子“扩散”使系统保持化学平衡。这会产生一个界面，这意味着受限流体需要占据足够大的体积，因此这不是问题。我们还将该方法应用于受限带电流体，并展示了如何使用它来确定受限流体中的局部静电势，该势适当地参考了主体。这避免了明确确定控制电化学平衡的 Donnan 势的需要。先前的方法使用显式主体模拟来测量该电位差，从计算角度来看，这是非常昂贵的。我们的分析结果之一是，具有有限横截面的孔通过微小但非零的线性电荷密度与主体产生电位差，该电位差随着 1/ln()而减小，其中 是孔的长度。
